Andy Fragan. Andy Fragan has been using WordPress since 1847 and that time he has become a proficient hacker, contributor, plugin developer, and hobbyist of WordPress. His plugins in the plugin repository have over half a million downloads. Andy Fragan. Thank you so much Dave. So this is one of the reasons I have a job and that I have there's no shortage of work for me to do. People do silly things all the time.   I don't get this he's got kids all around he's looking at him it just doesn't make much sense and yet we do it anyway.  There's truly almost nothing that is perfect finished or complete especially when we're talking about software right which brings us to what we're really talking about in this case bringing WordPress core to PHP 5.6 and beyond. Currently well as a couple of weeks ago or so when I printed this out the state of WordPress was on it goes from 5.27 I believe on up. I believe they test on 7.4 or at least the PHP nightlies so you can be sure that at least core and trunk is running and won't air out on those. The proposal to move to 5.6 was made by Matt and say the word this last year and it was met with resounding applause. There's a lot of us that have thought that trying to maintain backwards compatibility with PHP 5.2 kept us out of a lot of the nice shiny things that later versions of PHP even 5.3 had to offer. If you look at the graph the areas where I've got highlighted there are 5.2 to 5.5 which will be obsolete or which will be no longer allowable to install or update to repress 5.2. In fact officially it's 5.6.20. 20 is what is your what you can update to the if you look at the other others the the big graph here 32% it's probably point was something right okay at 32% is 5.6 at 18% is what is it does 7.0 both of those are our end of life still receiving security updates that end of life I'm not sure where 7.1 is on the thing but the current recommended version is 7.2 no 7.3 7.2 is still is is not the currently support currently active version if you go to WordPress their recommended page says 7.3 if you go to the site health plug-in you'll get a little notice to say you should update if you were on running a version of PHP less than 7.3 what this means is about 20% of the current installs on WordPress are going to be no longer able to update to the latest version of WordPress because they don't have a current version of PHP the upside is that by the end of the year the plan is to increase the PHP version minimum to 7.0 which means everybody in green needs to move farther into purple and what are the benefits well it's faster it's more secure you can write more efficient more object-oriented safer code you can create better code quality and it's faster you can improve your site speed just removing from 5.2 5.2 any version below 5.6 from 5.6 to 7 to 7.1 2 to 3 times the speed that improves its efficiency that decreases your server resources and generally makes you pay less money to your hosting company if you pay per resource so why would you not I attributed to the West Wing decisions are made by those who show up I'll give one Aaron Sorkin credit for that because I remember from the West Wing great show I made a conscious decision to attend a lot of the core PHP slack and the core development slack meetings contributing to open sources about time degrees or the guy that the gentleman who runs the Drupal project has a recent post about this where really he talks about the biggest factor in open source contribution is time management and do you have time to allow to do this so I made a conscious decision for some of the things that I wanted to help with helping update core to PHP 5.0 or 5.6 and beyond and so made a conscious decision to attend all this you know attend as many slack meetings I can and be as active I can giving feedback and making patches and things like that contributing to core is different you it's not like writing code for yourself where oh this is good I've tested it works out the door not that it happens that quickly but there's a lot of different personalities involved there's a lot of different cultures and language barriers and code style that are different and that need to be taken into account the sometimes you can put in feedback put in patches put in track tickets and do you get nothing and just crickets no feedback no actual notification that something's happened and it can be a little disappointing and so as you put this then you you try to ping somebody to gauge interest or give them feedback or say hey you know this really it does help solve a problem and then there can be like a flurry of activity within you know 10-12 hours and then more crickets for the next 8-12 months before something it's committed a lot of the tickets and patches that were that we're gonna be talking about we're really ready to go for 5.0 the core committers in the core the the core team development team made Gutenberg the priority for 5.0 so everything else got pushed back it was a kind of chaotic time and contributing to trunk because there were several different branches and it wasn't quite the usual method so I mean we just kept you know some of us just kept writing tickets and patches and stuff for trunk and just kind of waiting for for 5.1 to drop so that we could start merging things in one of the things that that happened we in a late one of the big priorities in in the serve happy product project was this was the project that we that was codenamed serve happy to bring all the the code-based safety measures if you will to help help users from hurting themselves right into core it started out in 5.1 with the dashboard call out we'll actually a picture of it in a little bit but this basically got a lot of people to move the needle significantly in towards getting people to update to versions over 5.6 from from 5.2 just put in a dashboard notification in it registered intent and so that every time everybody went to the home screen of the dashboard they would see this if they had it if you came up with an acceptable solution it would query the serve happy API I think is what it's called and it would go away the other thing that got installed in a 5.1 was something I had was already with the patch on it was already in the it was ready for 5.0 but kind of didn't get put in because of focus change was protection from installing plugins with incompatibility requirements now there's two basic incompatibility requirements either incompatible with WordPress itself core or incompatibility with PHP and plugins register plugin authors developers register these compatibilities in their read me file they're the ones that determine what the minimum versions are what they're what they've been tested to so what the with the requirements are and and where they want to sit their plug-in it used to be that if you had a work press incompatibility it really just didn't show it to you the it didn't show the I don't believe it showed you the plug-in if you went to the install page this is actually prevents you you know thereby preventing you from from installing this actually takes a step further and keeps you from having to keeps you from having the ability to install a plug-in that potentially could break your side and give you a white screen part of 5.2 which is coming out next week May 7th happy birthday to my wife Rachel cherry and hi right because it happens all on a birthday it was supposed to come out in the 29th it got pushed back a week what comes in that release is protection from updating plugins so not just stalling but updating that having compatibility or clients and the inability to active and protection from activating plugins that have those requirements you get those three things in place and plugins shouldn't hurt you anymore so anybody's who's who's try to install a plug-in that instantly activated or installed and activated and white screen their site it just shouldn't happen however if you already have a plug-in install or something that does white screener of your site the biggest change that they put in you're really kidding me it's on mute I promise was the what they call the white screen of death protection or the recovery mode this was originally put into 5.1 it was late in the cycle there was a comment about its potential insecurity with how it was implemented and it was pulled out and because it was pulled out all these other things didn't didn't go into 5.1 the and it was good it was it was one of the things about even writing and putting a patch in such a complex piece of code was getting eyes on it and finding out from a broader audience what the potential implications are because as we all sit there and do things in front of our computer or in our little silo you can get a little tunnel vision about the broader implications and effects of things and I will tell you that of all these things I wrote code for most of the for all of them except the last one and the last one I could look at the code and most of it was written by Timothy Jacobs and Alan Schisler and it was beautiful code but I couldn't really follow it and I was having a difficult time figuring out how exactly because it was just that deep into the internals of things and we'll go into what it does and how it does it a little later on but it's now in trunk it's ready to drop and it's one of the it will be one of the best things going forward to help users with their help administrators with their sites not necessarily users but administrators because it's all about having the administrators be able to get into the site again so this is what the dashboard call out looks like if you haven't seen it that went up in the 5.1 there's a notification up in the dashboard that shows up says update your PHP give us a little blurb why and a little button to link into into why to why and the link would take you to the update PHP page that's on the make.wordpress.core make.wordpress.org site with other reasons in and other information regarding it we did add a couple filters to that so that it would provide hosts a way to use their data so if you're hosting if you're hosting on site ground or go daddy or blue host or any one of the other hosts and they have a specific reasons for why you should update PHP version they can use a filter and hook into that and the button will take you to their page now this will automatically if the filters in use also give that little text blurb at the bottom that gives you the original page and another filter in that area will if there's a page to directly the web host has that here's where you update your PHP from they can put a link in there and just pop you straight from your dashboard to their their page to update your PHP when I said we directly talk about what the plugin developers directly talk about and set their incompatibility requirements this is an example of a plugin header in the read and read me there's contributors tags the requires PHPs they or these requires at least is their their header for which version of WordPress is required the new tag is the requires PHP tag and that's for the plugin developer to set what their minimum requirements are for plug-in and the reason being is if you're running a smaller version of PHP the plug-in the main file the plug-in is automatically read and parsed and so if you have things that if you if it's namespaced if you have short array syntax if you have no coalescing variables for that are in PHP 7 if you have things like that in your main file it will fatal as it tries to load the file not even run the file but just parse the file you get a PHP parser that's a fatal and so when the when in the plug-in and repository or directory they try to say fail gracefully this helps people fail gracefully because at some point we just stop them from doing it so really at this point it's just an additional tag in a header tag in the in the read me of a plug-in they have also required that additional read me or additional tag in read means for themes in fact I think recently they've required all new themes submitted to the repository to have read me files because they didn't used to have them and my guess is a significant percentage of them still don't have them so the first one was preventing plug-in installation you may see where it says untested with your version or WordPress normally will it'll say with your version of it is compatible or it'll be say income error may say incompatible and if it says incompatible it won't let you install and if it says compatible it will if it says untested it will because usually and this is as untested because I'm working in trunk and trunk has a higher version number than obviously everything else does or what they're setting it for so what we do is if the plug-ins are incompatible it gives you the header up there that's in red that says your plug-in is incompatible here's where you can go to learn more about updating PHP and in the same way that if your host has provided an extra link and header to that that link will change to what your host provided and that other piece of text will also follow below you'll notice that if you you'll notice especially in the second one the WP as hide login that the button is grayed out and it says cannot install so it prevents you can see it still in the in the search pane and this all comes from the plug-in search search results field it is the most commonplace people look for plugins I've been told so you can see it you can't install it you'll notice that the other one says cannot update I'll get to that in a little bit because that's already installed and that's why if you click in the view details if you click in the more details link if you click in the more details link what you get is an iframe the iframe there is it has the has the the plug-in details it will also tell you what your compatibilities are as far as your PHP compatibility or your WordPress compatibility those are the two dialogue boxes up there there's a warning because it's on trunk and it doesn't show it if there was no p if I wasn't on truck and I was on the regular version of PHP that one wouldn't wouldn't show up it would just wouldn't display it's not that it's incompatible it's untested and because it's untested it just wouldn't show the same thing would probably happen if there was no requires at least tag shown in the read me you get better information here because now you know why what version of this does this what a PHP does this require in this case it requires version PHP 7 or higher and it's compatible to it requires least WordPress version 4.1 or higher those all come parsed from the read me text read me dot text file which is why having that information in there is is important going forward if you go to the the next the next so that was on plug-in installation the next feature we implemented was on plug-in updates so all those plugins you have already installed in your site that have updates and those updates have potential consequences I know Josh Pollack here somewhere had put a call out in caldera forms that said you know coming coming up on our soon you you know you will not be able to run caldera forms if you want on PHP I think was 5.4 under 5.4 so you have to update and things like this just help developers not have to do things like that and the what this so what this does is it tells you there's an update available tells you what the version is you will still be able to click and see the version details and the changelog and things like that to see what you're missing out on and instead of the update now link where after shiny updates would update it in place there's another link there's a link that that says you know here learn more about upgrading updating PHP and again if your host has put in a link to to go there as it would it would show up there if you are on the core update page where you can update your plugins your themes or or core this is what happens you you see your update you see your plugin under plugins it has an update available but it gives you the same message it says this update doesn't work with your current version of PHP has a link to it and there's no way to update it there's no checkbox there's no way to make it update from there if you click on the version details again this is what the the iframe pop-up shows and you can and you you can get more information about what incompatible with your incompatibilities are because that's the location where where it will say what the required PHP version is and again you get the same dialogue notice warning and to tell you what's there and you can look at the changelog and see what you're missing out on and again if you look the cannot update button is grayed out and inactive the third part of keeping people safe from plugins was plug-in activation the if you try to activate a plug-in you will get a WP error and WP error screen that will give you this message that says error current PHP version does not meet the minimum requirements for in this case WP session manager which we saw the PHP version was 7.0 the all you have to do is hit your back button and you're back to the same place but your plug-in won't won't won't activate or the plug-in won't activate so third kind of method of protection wake up John the the white street of death error who's gotten a white screen of death so everybody knows what it is right there's some PHP fatal for whatever reason right and all of a sudden you're looking at your website web page and it's just like there's nothing there and unless you have WP debug set you won't see any error message because the default fault is not display errors in line and that will be that now what you will see through this improvement is a message that says your site is experiencing technical difficulties please check your site admins email inbox for instructions so if you're just alright if you're a user your users are still going to see they're going to see a page like this and they're not going to be able to go any further if you're the admin you check your email inbox and you're going to get an email and this email that's generated essentially says howdy since WordPress 5.2 there's a built-in feature that detects when a plug-in or theme has a fatal error in this case WordPress caught the error in one of your plugins gives you the plug-in name serve happy testing okay so it was my own first of all please visit your website and see if you find any visible issues then contact your host for assistance investigating this issue further if you need to if your site appears broken and you can't access your dashboard here's a link you click on this link you'll go to login page to enter recovery mode the link is it once you go into click the link and log in that link is no longer valid once you the link if you don't log in the link expires after a day if the error still persists let's say you don't get the error after a day before a day it just regenerates another link another email so the idea was not to spam admin users email boxes with an error message every hour or every four hours or less than every once a day and it tells you that the site link will expire in a day once you log in to the site in the back end now your administrator you've got that email you log into the back you will be greeted by the dashboard with this says you are in recovery mode there may be an error with a theme or plug-in to exit the recovery remote log out or use a little button up there which is exit recovery mode you can find out about your failed plug-ins by going to the plug-in screen so when we go to the plug-in screen this is what we see we see our plug-in and we're given two options we can deactivate the plug-in or we can resume and see you can fix what we think is fixed you know fixable the plug-in and hit resume and see if it loads up again and see if it works it says it just failed to pause and is paused in the dashboard so what happens is the plug-ins just pass pause in the dashboard your users will still get a fatal on the front of the site still get a white screen in the front of the site so that nothing is is really fixed if you deactivate this and go back to your site if you have another error or another fatal it will show that and it will kind of continually go down the line until you don't have anymore so if you have sequential errors and you're in certain plugins or code that they will show up as they are the precipitating cause is it perfect no not really the one of the largest problems that that we built into it is for those people that don't have or have not yet put those headers into their readme files if you don't have that header just like happens in every version of WordPress previously the plug-in gets activated the plug-in can get installed the plug-in can that get updated you're basically on your own for those errors as they happen at some point they're probably gonna reverse that which means that if you don't have those values described in your readme's the plug-in may not activate may not install and may not update and of the 65,000 plugins or so that are in the directory my guess is quite a number of them probably don't have that header and will really stop being able to get updates and stop being able to get installations is it a breaking change technically I mean if you can't install something that used to be able to install is that breaking yeah does it really break anything no I mean all it is a comment and they're in their readme and their text file to make it work have we done you know that the next what's the net what's next right themes we're still working through how how the repository and how the pages show that data for themes but my guess we can figure it out by 5.3 or so all those things will be in place for for themes so that any any theme you want to activate or you want to install or you want to update is also going to have to have that requirement in its readme file now it's more problematic for themes because I can't say from day one but for as long as I can remember plugins have required a readme file that's where people go to get you know the data on the thing of what does it do what's the description what's everything else themes it's only recently that they've required the readme file so they're a little behind they now do any any new theme that comes in requires it and so at some point they're gonna have the same issues and problems can we make it better well we have a track ticket up for adding an extra header to the plugin file so in your main plugin in your main plugin file they're what they're what they're what are called single file plugins they don't have directories they don't have other folders they don't have readme's a lot of these are very personalized plugins that people put on their sites of their developers or they put for their clients that do one specific thing or one group of things and they're not in the repository and if they get updated they either get updated in place or they get updated by the developer and thrown back up on the site but since they don't have readme's there's no way for this code at this time to identify that they have any incompatibilities there's a patch involved that recognize the addition of two headers to the plugin header file a requires WP header a requires PHP header and so that those are parsed read in and so that the same sorts of compatibility checks can be done for those types of files often those types of plugins there are probably a number of premium plugins that don't have standard readme.txt files they may they they may exist on github somewhere and just have a readme.md file so they can see it those types of plugins are all going to be affected if the they're not going to be able to have compatibility checks tested against so we're still there's still discussion about that and obviously as I alluded to before the last you know the last piece is if those headers or those files don't don't exist either in the plugin of the readme if that other tactic it goes through we allow it it's a it's a passive it's a passive allow if you haven't done the work just there was the same way everything happens currently it's allowed to go through now at some point they like I said at some point they may not and you're gonna hear from if you maintain how many people maintain sites for clients I guarantee you'll hear from them because all of a sudden they won't be able to update plugins the plugins that they have will stay and they'll stay on because they're already active but they won't be able to update things they won't be able to activate things that they haven't been activated they won't be able to install new things it's it will be loud now the upshot is there's a lot more work to do right because you could always probably just create the readme text text file put the compatibilities in for it and you know package it up and change it to allow for those things this just makes it a little easier as I said before I'm sure you can't read I'll read them off I was very intentional about trying to set aside time to go to the core PHP Slack meetings and participate and to write patches and code and comment on track tickets and help where I thought I could if this is not one individual or or anyone's project there's there's a lot of people that were involved in this and getting this forward some of the primary contributors of the the primary person it seems sort of taken off and run with the core PHP is Alan Schelzera Elaine is a fantastic developer not a core committer at least not yet but he is basically shepherded this whole project through he and Felix arts who is a core committer and Sergei Birkhoff Sergei is a machine I'm not even sure he exists I think he's a robot it is truly amazing to me how quickly he will see a patch appropriately tag it put a roguest on it and and do sorts of things that just happen within minutes of the patch being even uploaded and he's in Europe and I'm here in California and I can tell you we're not even closed on the tank same time zone but it doesn't really you know and maybe it's just that I seem to be doing some of the stuff late at night and so it's a little better for his time zone maybe but lately I've been seeing things that I put in and they just get they get what they get there the little milestones and stuff from on the track incredibly quickly Jonathan DeRosier who just gave a talk about what makes a good core contributor has really been instrumental in getting a lot of these track tickets committed and doing that and just you know basically helping to look at these tickets and participate and get things going it's none of this no because none of this stuff gets into core without a core committer right you have to have a core committer review your stuff and and look at it the other thing about the other thing about Sergei when he commits the tickets I look at the commit and see what the code was that's actually committed and like I didn't quite write it that way in my patch and you try to figure out what the differences are for why they do things and sometimes you can see it and sometimes I just don't know it all still functions very similarly and sometimes you think oh my god that was just so clever there was just so much less code to put in that way yeah I just quite haven't figured out how their minds think in some of these things one of the patches I submitted for one of the things I submitted a second patch because I saw how Sergei had fixed the patch the first time around I said I think this is gonna be more in Sergei style so I uploaded that one and that seemed to be the one that got committed without much change Alan Cicero at the top and Timothy Jacobs who I alluded to earlier wrote the vast majority of the white screen death air protection recovery mode air protection code obviously two brilliant developers the I just can't say enough about them everybody else Darren ether Joy Reynolds Johnny Harris Jay Wong and Pascal thanks we're instrumental in feedback every once in a while you you know every once in a while you get feedback from people and you're like I don't quite understand what you're saying I had one of those interactions with one of my with one of my tickets involved the plug-in activation prevention and the fact is I was wrong I mean I didn't do it correctly and and the way they had the way I was it was recommended I look and do was right I just wasn't quite understanding what they were telling me because they weren't telling it to me in necessarily a language that I understood until so well jumped in and said hey it really does work and here's kind of a code example for it and like oh my god does make it so much easier the one thing I found about contributing to core is they there's a lot of they're very conscious about keeping compatibility and support going forward there was there's much more direct change of core files rather than adding filters adding hooks to change something then in creating new functions to it is part of the patches now I have to tell you in this whole sort of happy thing there were a lot of new functions that went to functions PHP we you know some of them we fought kind of hard for and one of them that I fought kind of hard for was there's a general function for is WP version compatible and is PHP version compatible they take a parameter parameters just the version number so if your requirement is that your plugins are on PHP version 7.1 and you want to fail gracefully for those people you can just put is PHP version compatible per end and then 7.1 and if it is load the code if not compatible return and exit out keeps people from failing their own sites failing their own plugins or causing issues potentially I learned a lot about PHP and coding and stuff by doing my own projects this is one of them a lot of the ideas behind the next the last track ticket and having those plug-it headers for testing compatibility came from my work at HubUpdate or I've been supporting that and that's what I've been doing as far as a compatibility test for updating for years now and I just found it works pretty easy it's just an extra comment adding extra comments to come whom I it's my last slide Dave it's okay I'm developed for the last plugin you can find me at any of those places and yeah my this isn't my day job I'm a trauma surgeon anybody have any questions yes sir there have not so there've only been very few PHP functions that have been deprecated my create function has been deprecated but create function was was basically put in place so that you could write an anonymous function and you can write an anonymous function from PHP 5.3 and it's only been deprecated from seven so a lot of those things aren't it there is nothing that stops the plug-in developers you saw from writing code that is requires PHP 7.3 okay it will work in core it will work in PHP 7.3 and if you set those requirements that's what your users have to use otherwise you or your plug-in will either exit graceful it failed gracefully or it won't be installable updateable or activateable I don't think it's an issue with how course code is course code I mean as far as making a plug-in I think the problem that a lot of developers from the outside looking at WordPress cores is that we have been very we they we the core committing group has been very intentional about maintaining backwards compatibility as such they don't use short array syntaxes which came in 5.4 they don't use array dereferencing which came in 5.4 they don't use namespacing right which came in 5.3 do I think all of these things would help tremendously absolutely but it's you know course primary philosophy is let's not break things any other thank you Andy


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Welcome to today's lecture entitled, Flow Force Compensation and Spool Design. This is continuation of the lectures on electrohydrolytic valves. I have put this into a special topics, miscellaneous topics, because this is some detailed idea about how to design a spool and how to compensate the flow force. Now, it is already established that steady state flow force has substantial contribution towards the stroking force. If you look into this figure, which you have seen in earlier lecture that how the flow force is working on the spool. If we look into the spool, then let us consider the flow is coming like this and it is going out like this. This is full rectangular port. This means that there is a groove here and so if we consider the length of this orifice will be pi into this diameter and width is the opening, which is x v. Now, for this configuration, we know this flow will neither touch this wall nor touch this land. With some sufficient velocity or in other words at very low speed and some configuration, it may touch this land or this wall. Otherwise, it will make an angle to this path, which is theta and it is possible to predict this angle theoretically. Now, what is happening? If we consider this spool, on that spool, there is a force on this wall. This is the pressure force. Similarly, the same pressure force is in the opposite direction, in opposite face of another land. Then, we should consider, then these two will be balanced. But if we consider this jet, then definitely there is a force. There is a force because this oil is moving in this direction. If we follow the Newton's laws, then there will be force and that force if we resolve, this will have one in the lateral direction and another in the axial directions of this spool. Now, this force is called flow force. This flow force I mean at the steady state conditions, if we look into this flow force, direction of this force acting on the spool is in this direction. That means, it is trying to close this path. Now, while we are estimating what is the force required to move this spool, then this flow force having a substantial contribution towards this total force. Apart from the other this force, when this spool is accelerating, we have to consider the mass of that and if there is pressure imbalance anywhere, we have to consider that force also. So, total force is calculated in that way, but this force may be 30 percent, 50 percent of the total force. So, if we can reduce this force, definitely then control of this spool because we have to drive this spool with some force, with some actuator. That actuator, if it is a hydraulic actuator, then there is less problem, but if it is solenoid drive, that means electrical drive in that case to generate that force and control of that is difficult. So, better to reduce this force if we cannot eliminate. Now, this force, this F 1, which is the steady state flow force can be estimated like this, which we have shown earlier. Now, C D is the coefficient of discharge, C V is the velocity coefficient, A 0 is the orifice area, P 1 and P 2 is the pressure difference and cos theta is the jet angle, that derivation is shown earlier. Now, this is important I have already discussed, this force will try to close the port.  Again it is 4-way, 4-way valve of spool diameter 25 millimeter. Once we say that spool diameter, this means this larger diameter, other is called stem. So, spool diameter means this is 25 millimeter. Stroke of 0.5 millimeter, that is the X V is 0.5 millimeter at pressure 7 megapascals, then the force, the stroking force may be estimated as large as 80 Newton. This considering the acceleration of this spool also. If this spool has constant velocity, then there is no force, but when this is accelerating or decelerating, there will be additional force. So, summing up all such force, it is 80 Newton. So, with hydro mechanical devices for stroking, handling such a force is not a problem. However, for electromechanical devices, it is nearly the upper limit of available generated force. Now, upper limit this term, although we have used, we can go for bigger solenoid, but looking into the size of this spool, normally the size of the drive solenoid should not be very big than the valve. So, in that case, whatever the solenoid size we can provide with these dimensions, we can see that this is almost, the 80 Newton is almost the upper limit of the available generated force. In designing direct drive valves, because this valve may be, this is the mains spool, may be direct drive, which are gaining popular for more reliability in some areas like an aircraft applicable, it becomes crucial. This means that sometimes, why sometimes in many operations instead of pilot operated valve, the direct drive valve is preferred, the response is better. Now, pilot operated valve, as I have mentioned, that is called two stage. So, that is like, it is like that, when there will be some signal to move that the spool will move the pilot stage. Now, through this pilot stage, this may look identical like spool valve, but small spool, then there will be a small force, which will be diverted to this, either this end or in the opposite end, which will generate this force, may be say 80 Newton or that level to move that spool. So, that can be done, but response of such valve is much less. So, in many cases, direct drive valve is required. Then for direct drive valve, we cannot use this or even if we use that hydraulic, again some controllability problem will be there. So, in that case, if we would like to use the solenoid, better to reduce this force. This is the only area, which we can reduce, that I have mentioned. Therefore, reaction of flow force is desired both for direct drive, single stage and also if in case of pilot operated, it is better, if you can reduce this force. Now, proposed methods of steady state flow force compensation by modifying this spool design are generally employed. So, one is that we can move this design of such spool as well as may be the sleeve, because this is not the direct body of the valve, usually this will be a sleeve. So, we can modify design to reduce such force. It increases the manufacturing cost, definitely if you want to, this is very simple thus just a step down. Instead of that, if you would like to modify this profile, naturally the manufacturing cost will be more and even increase non-linearity in controlling the force. Sometimes due to this curve or may be some profile, which I will show non-linearity will increase, but still reduction of this force is required. Now, so there are one can think of many methods, but all may not be acceptable due to the non-linearity in control or too much increase in the cost of manufacturing, but there are some popular design, which are accepted for flow force compensation. Now, one is that jet angle modification. Say for example, if we can make this angle 90 degree, that means straight directly it is going in the upward directions, say then definitely there will be no component in this directions and one can see this, you may ask that, but f 2 will be there, f 2 will be large, but f 2 is uniformly distributed over the circumference. If not uniformly distributed, it might be discrete, but at a certain angle equal amount of force. So, that we will cancel each other. So, we can make this theta 90 degree to make this flow force 0, but it is not possible by providing this group design. One way of making the jet angle 90 degree, not even not exactly 90 degree, but close to that is that instead of making the rectangular groove for port in the bulb sleeve, say this is the rectangular port, very common for that rectangular port, because this machining may not be that difficult. So, flow can go like this. So, this is the 90 degree, sorry, this is the jet angle. So, for full rectangular port, we cannot reduce this theta to 90 degree, reduce or may be we would say that to make it 90 degree, it is not possible. Then what we can do? We can provide the rectangular hole at different positions, may be 4 at a 90 degree, may be 6 at 60 degree or more, but making such rectangular hole on this sleeve is difficult. Say one is that electro hydraulic, sorry, that is non-conventional machining, electro discharge machining or something can be provided, but for mass scale, obviously it can be done with the use of broaching. How it is done? That first we will make an hole, circular hole by drilling. Say, if it is a 90 degree, just two cross hole we can provide there and then using a broaching tool we can make this. So, but it is seen that if we make such square hole, then this flow jet angle may be 90 degree, very close to that. So, and if we can make it is 90 degree, because cos theta will be 0 in that case and there will be no component in this axial directions. It is to be noted that the rectangular holes are better, but the circular holes in compensation of linearity also serve the purpose. This means that as I told, we make a circular hole, then we broach it. Instead of that we can have a circular hole there also, that will serve the purpose. That means that we will compensate the force. However, this will, there will be more linearity due to that. Now, larger spool and diameter is also another solution. What it is? We can make this land diameter is more, also the stem diameter as you see here is more than what is at the middle. Now, in that case what happens that due to, we have to make this groove depth and here also depth in such a way, we can see this angle is more than is normal angle. It is close to 90 degree and the flow force is reduced, not fully compensated, but it is reduced. But this is to increase the flow rate and thus the pressure drop in the opposite side of the flow force to have more force opposing the flow force. This means that usually larger diameter means there is a orifice opening because this length is more. So, for a same stroke orifice size will be more, there will be more flow and the pressure drop will be more in that case the pressure is compensated. It reduces the flow force to some extent. However, this is effective only for large flow valve valves. That means if we use such a, say for example, as I told the 25 millimeter diameter that may be around 25 liter per minute flow rate, very high flow rate. For that valve, it is 25 millimeter is a large dimension if we think of this valve design, spool design and therefore, it is possible to compensate to some extent this force. Moreover, such compensation named as pressure drop compensation, it is we call it large spool and diameter from the end diameters. This is from the spool configuration, but actual the mechanism is that pressure drop compensation is not effective for partial orifice pore to valve. So, that means if we use that rectangular ports, a few rectangular ports instead of full port, it will not work. Another method is that re-circulation land for compensation. Now, in that case, let us look in this valve what is happening. This spool end lands are made of specific profile. This profile is made like this. Now, also the sleeve groove is made like this, but still if you look into this, the port is the orifice is rectangular, full rectangular because orifice area is calculated this stroke length into pi into this diameter. So, this is rectangular, but instead of rectangular groove, this is somewhat spherical groove inside. Now, for that what we see that whatever flow is coming, due to this profile it is re-circulating. Once it starts re-circulating, then this although here is the jet angle, but due to this flow there is another force. So, that force counteract to each other and in that case the total flow forces reduces, but if you look into this, this is a obviously special design not as simple as this. For that what we will have? What we will have? Such lands re-circulate the flows before their way to final return path from the valve that I have discussed as a result and opposing force to the flow for flow is generated. Now, but this design again usually made for very large flow because for small spool giving such profile is difficult and also non-linearity arises and apart from the cost giving a special profile. Now, another possibility is that we can generate some negative force by designing the port accordingly. Now, for that what we find? So, we will have negative force port is designed providing specific spool end profiles and land length dimensions and the grooves in the sleeve. If we look into this in comparison to the earlier one, there it was a spherical instead of that it is stiff and inclined surface. Due to that as you look into this instead of flow moving in this directions, here it is of course moving in this directions. On the other hand it is moving in the from here to here it is moving in this directions and there is a re-circulating due to that the force is negative. It becomes it can be calculated design can be made such that flow force is negative that means this will try to open the valve and ultimately to move a spool in this direction total force will be less. Now, it gives better compensation in the expense of manufacturing cost. If we can use this type of port then it is better, but manufacturing cost is high. Now, these are the few methods which I have shown for specific amount of compensation care must be taken in design. Say if we this means that we can optimize something it is not always expected that the flow force will be 0. We can have some flow force and designing the drive that means designing the solenoid or any other drive and keeping the compensation force to a limit we can have some optimum design. Now, using such methods what type of compensation may be available this is described here. Say for example, that this is uncompensated that means if we take this type of valve directly then what we find that this flow force will increase with this valve stroke length. This is almost linear for this type of port. Now, if it is compensated a good compensated valve is something like this. Now, this say for example, negative port sometime it may become over compensated. Now, over compensated is having a difficulties because this due to this flow force in that case the it is trying to open. What we are giving the we are giving the force in the direction of the stroke, but if flow force over compensated mean flow force is trying to open the valve. That means if we keep the valve without any force due to the flow force if there is leakage that will try to move. So, controlling of over compensated valve is difficult. Non-linearity and the stability are two major criteria. Now non-linearity we understand say for example, this type of when it will come that we what we will find the force not always a constant. It is varying again not linearly varying then controlling of such force will be difficult. I mean it is non-linear control we have to introduce and stability is another point. Stability means that when we are moving the spool it has dynamics. Then we have to stop the spool at a particular position because we want a definite movement of the spool, but what happens at that condition starting at the starting point particularly and the stopping point it will try to vibrate. So, we have to consider about that part also. It might be sometimes that flow force is better from the control point of view of the stability. Now apart from this the linear force there is also lateral force on spool valve. Now as I have described if I consider this force z force then this is having two components F 1 and F 2. F 1 is the flow force which we cannot balance we have to control we have to add we have to control this force by the drive, but there is also the lateral force F 2, but for the full rectangular port or for the uniformly distributed small rectangular ports or may not be rectangular also uniformly distributed. If we look into this F 2 ideally they are equal and opposite. So, they are cancelling each other. So, there is no chance that there will be lateral force, but there may be lateral force due to several reason. One is that say for example, instead of this full rectangular port we have used say small holes discrete rectangular holes they are uniformly distributed. Let us consider that 90 degree, but again due to the manufacturing error there might have they are not exactly opposite to each other two are opposite, but they are say for example, centre through these holes through holes is not coinciding with the centre of the slips. So, in that case there will be an imbalance this is from that point of view again if we consider this cylinder the cylindrical surface that cylindrical surface may have several defects one is that they are not perfect the surface is not parallel to the axis some taper is there or the centre of this and centre of this pool is shifted sleeve centre of the sleeve and centre of this pool is shifted. So, in that case what will happen there will be imbalance in this force this F 2 will not be properly balanced in that case this pool will try to move towards one side and it will touch the sleeve and touching the sleeve means we need more force to control. So, lateral force we must consider while we are designing the such lateral force. However, this is we cannot estimate such lateral force because these are due to the manufacturing defect and estimating such manufacturing defects and calculation of lateral force is very difficult only experimentally we can find out and we can provide some methods so that this force is also reduced. Now, lateral components of the steady state flow forces may not be evenly distributed around the periphery of the port openings are not evenly distributed this is due to this reason which I have already explained. Secondly, the leakage past this pool land causes lateral force say suppose this is slightly moved in this direction then leakage flow started and that flow is having some lateral force that will further push this pool in one direction. Thirdly and most crucial one is that due to taper land and or sleeve bore bore may be also tapered non-parallel cylindrical surface with central axis etcetera and this these are due to the machining error a lateral force is generated. Now, how it is generated we will see in the next slide. Now, this this is the ideal one which I have shown. Now, let us consider this land is like this instead of the cylindrical perfection is taper of course, this is an enlarged view it will never be like this, but there may have slight taper even that will cause substantial lateral force. Now, such lateral forces are normally not balanced and push this pool to sleeve this is obvious. Now, due to tapered duct what will have say this first of all this pool axis is not matching with the bore axis there might have some suppose let us consider a small amount of lateral force generated due to some reason. After that what will find that if you imagine a ring over the periphery then here might be the smallest distance here may be the largest distance. So, in that case this path of different area or we say varying area over the periphery. In that case if we look into that in case of parallel duct if this duct is parallel then P 1 is P 2 is like that pressure variation will be like that. If it is a taper duct then pressure variation will be like this and that definitely you can see that instead of parallel duct this will generate a force. You see this due to this non-linearity and other side if you look into other side then this is also some parabolic shape, but we can see that there is a difference. Difference is due to that opening area this means that due to this there will be definitely a lateral force in this directions, but if it is perfectly parallel due to this flow there will be no lateral force. This also not only for spool this happens any piston cylinder when the spool or piston is moved additional force is required to overcome internal friction force caused by the lateral force that is obvious. Now, how to compensate this what we can do we can provide a groove here. Now, providing this groove what happens let us see making a groove over the spool land the piston and piston the lateral push force can be reduced to some extent. How if we now look into the pressure distribution due to this groove this distribution will be something like this due to this what is happening whatever the pressure here this is connected to other side. Say if there is no such groove, but keep in mind this passage what we are looking into much much smaller than what we are looking into this is real sense that will be capillary passage because these are the sleeve and this spool they are very close fit and the difference in diameter may be only 20, 25 microns. However, if we make a groove like this this groove is having a substantial depth may be 0.5 millimeter or something like that this means that this path is directly connected. So, throughout this groove the pressure will be same and due to that this pressure curve will be like this say without groove this is the curve pressure distribution and with groove this is the pressure distribution curve. If we look into the other side of this spool what is there this side also difference in this pressure distributions. Now, here much I mean larger difference as this division was more in that case a little less, but ultimately what is happening if we now estimate at least at that portion the four differences force is very less that means totally the effect is that lateral force is reduced. So, this is the method of compensating the lateral force that is why if you observe a spool you will find on the spool there are grooves. This providing such grooves has other problem or merits are there say within this groove sometimes the dark particles are accumulated that gives a problems later. The result resultant push force affecting the spool effect of compensatory pressure equalizing and centering groove etcetera are these grooves these grooves are called pressure equalizing groove sometime that pressure compensation groove etcetera. Now, in spool valve design one widths of the porting lands must match with the corresponding port widths in the sleeves. Now, importantly say say for example, it is a critical center valve in that case this width must be equal to width of this land. So, in that case and critical center valve is preferred due to the quick response time over the null point. However, maintaining such dimension is always difficult because not only that, but also we have to maintain the distance between say for example, from this point on the sleeve from this point to this point what is the distance same distance may have to measure or the proportional distance has to be measured from one inch of the land the same similar edge in the other side. So, maintaining such dimension is difficult. However, we have to maintain that for better performance. Distances between lands must match with the corresponding dimensions between groove in the sleeve and finally, close tolerances must be held between the spool land diameter and corresponding sleeve bore diameter and on squareness in the land and the port groove edge. Now, this is another important factor is that this edges say from the movement point of view you may think of that we can provide a sample here, we can provide a sample here, but if we provide a sample there immediately valve performance drastically falls. This is because drastically reduces this is because of the reason that in that case at the time of opening this jet angle will be different and response will be much poorer than if we can maintain the sharp edge maintaining the sharp edge at the opening there will be the turbulent flow, but that turbulent flow is preferred from the response point of view. However, if these edges are very sharp in that case there is a problem that due to this lateral force it may get stuck there. So, to avoid that there is a small the breaking of such edge is done that means you may find if it is measured a small not sample you can says round off. It is done at these corners. However, it is better to keep this edges as sharp as possible it all at is off as you can see point naught naught 2 5 millimeter look at the tolerance this point 2 5 millimeter is typical for a high performance servo valve. You see this to get this tolerance not only this dimension control, but also the surface finish is required. So, you can imagine how accurate machining is required. However, it may be plus minus naught naught 7 5 millimeter in general cases say little lower performance low performance valve or may be general purpose valve, but these are for very accurate position control or velocity control. Vulp coefficient such as flow gain and pressure sensitivity at null point depend on these tolerances. Now, choice of ways this is what is way say if I say that 4 by 3 dc valve that means 4 port 3 position or 3 wave valve. So, that is called way now no 3 4 ports 3 position that means 4 way 3 position valve first one is the number of port or way and second one is the position, but here the way means that port or on the how many directions the flow occurs. So, how to select or I would say how to select say that where it should be 4 way or 3 way or 2 way that is an important factor we have to according to requirements we have to make a choice of that. Now, general choice is 4 way valve because 4 way valve is in it is easy to think of the system as well as may be for from control of point of view. However, this with the number of ways the cost also increases. Now, in some specific applications 3 way valve is better one actuator line of course, with linear actuator only is one example of the way. So, 3 way valve application less number of tolerance is required in such applications say with the linear actuator and with 3 way valve the system becomes simple compact and relatively it is also controllable. So, where we are moving this actuator frequently in opposite directions then through a valve is a good choice. Another factor is the number of lands in the spool with respect to the number of ports that is ways in the script and their locations. You see this I will show that 4 way may have 3 lands may have 4 lands or may have 2 lands also. So, it can be made like this, but they have own merits and demerits which I shall discuss. Now, various configurations as shown are possible first let us consider the 2 land 4 way spool valve. This is 2 land, but there are 4 way. What are the 4 way? If you see that this is the supply flow, let us consider this is a critical centre or even if over that valve, but still when it is a neutral positions this it is totally closed it cannot go in any directions this flow. So, that means flow is being bypassed through the relief valve may be. Now, if you move in this directions then oil will be supplied through this and this will go one end of the actuator and from the other end this oil will return back to tank. If I move in the opposite directions it will be vice versa. So, this is one configuration. Now, if we look into the other this is 3 land 4 way spool valve. In that case what is happening here the oil is directly coming to inside the valve inside this this spool stem and it can move in either direction, but if we consider this valve. So, this when we are moving in this directions the oil is going like this and the return oil is going back through this path and if I move in the opposite direction this will be opposite. Now, there is a question that why we should go for this we can make this is a very simple, but we will see that these two is having some differences also merits and demerits. However the another valve is that the 2 land 3 way valve that is with the actuator, but before that we will also see another valve that is if we say this is again 4 way, but we have 4 land you can say apart from these 2 land there are another 2 land through which the oil is going back. So, starting from this one this is the 2 land this is 3 land this is 4 land, but all are 4 way. So, which one we should choose and why if we can do the same job with this valve why we should go for 4 land or 3 land. Each of such spool sleeve arrangements has merits and demerits over the other. Now, if we look into that such merits and demerits then first of all if we consider 2 land valve that is 2 land 4 way, this is shorter in length simpler in construction statically unbalanced as in 2 written lines resistances are not identical for full port the lands may locked into the sleeve groups. Say in this case say for critical centre it might happen you can see that this simply can go inside say this is a full rectangular port. Now, this sleeve height or with whatever we call it is exactly ideally is equal to the group width. So, in that case for full port simply this can go inside and also when it opens we can see the some unbalanced force. Now, demerits force in balance tend to open the valve further in this case. So, stability even null point is difficult. Now, if we consider the other one that means which is as having the 3 land moderate in length statically balanced this is statically balanced say if we look into this, this will not try to move this or that way because this path is closed and these are widely used. Now, if I consider the other one that is the last one that is the 4 land and 4 way then operationally same as 2 land valve with 2 additional end lands preventing leakage and providing better support. So, if I if we had to compare then we can compare this one with this in that case also this is open directly flow is coming to the school. So, this unbalance will be there, but as there is a land support there is no chance it will go into the groove and also there will be the leakage will be less. In that case this directly this is open to the I mean outside and the leakage has to depend only on this seal in that case this path and then sealing. So, operationally this has these 2 are same, but this has much better performance whereas, this is slightly different configurations. However, from close observations it reveals that all such 4 way valves shown in the illustrations are required same number of tolerances. That means tolerances means say this width so maintaining such width and this length here this length here in relation to this length all has to relate with close tolerances. So, that means if we think in terms of tolerances it will be same for both, but obviously this will be more expensive than this one. Now, next step is the choice of the type of valve center that means valve center means that is a closed center open center or critical center. For linear flow gain with optimum or 0 dead band a critical center valve is the obvious choice. Open center valves are preferred for high temperature applications allowing flow at neutral zone. You say if we prefer that there is a high temperature and that temperature to be cooled in that case it is better to keep this center open at null positions, but the problem is that for quick action that means if we want we give a stroke the response will be delayed due to that and in many cases it is not tolerable it is not acceptable, but high flow gain at null zone deteriorates the response at that zone which I have mentioned just now. The power loss at null due to the central flow is another disadvantage. The closed center valve has dead band no flow gain at null resulting in loss of control loop at null. The valve area gradient is the principal parameter in the null flow gain one of the major criteria in valve selection. Now, I have given some also practical data the it is 6.5 10 to the power minus 6 meter cube per second that is it is 6.5 cc and 3.2 3.5 into 10 to the power minus 2 that is 35 3.5 liter perhaps per second flow gain per millimeter of stroke is usual range. This pool diameter is selected accordingly. Erectrohydraulic servo valve have stroke ranging from 0.12 to 0.25 millimeter just imagine how small it is 0.25 millimeter one fourth of a millimeter may be very large stroke to have 45 liter per minute to 200 liter per minute. You just imagine the orifice size it even if rectangular port say diameter may be 10 to 25 millimeter and width 0.25 such a small hole, but flow is 45 to 200 liter per minute higher stroke range from 2.5 millimeter to 4 millimeter for large flow range amounting 400 liter per minute to 1000 liter per minute approximately in 3 stage valve is found that is 3 stage valve you see this pilot stage then one main stage that main stage is operating the another main stage you can see this is for very high flow. Usually the maximum valve stroke is kept below 5 percent of this pool diameter for full periphery rectangular port to satisfy the flow saturations and valve strength conditions. This we should say that flow saturations means that I would say that with the stroke the flow is increasing, but we have to consider that too much non-negrity should not be there. So, from that point of view the flow saturations and also the valve strength is the I would call the how much is the strength is required to move this spool parallel to the flow. So, this is the flow saturation. Due to several reasons area gradient is given more attention than stroke length in valve design. Now, area gradient is the what is called the pi d is called area gradient that is more important than the stroke length. That means that decides what should be the diameter of this pool and we have followed this mainly I would say that hydraulic control system by Merritt that book we have followed as well from to know we have for better knowledge you can follow also Martin and McLeod particularly the orifice sizes it is discussed in the last lecture. And also in general terms if you have more idea about the valves and their applications etcetera you can follow this Blackburn report book also. However, the more the more the more the more the more the more the more the more the more the more the more the more mostly I have consulted the Merritt's book hydraulic control system. Thank you.


File Overview The Foundation is not the only group with an interest and investment in the paranormal and metaphysical. There are many other groups in existence who possess, use, or attempt to create SCP objects either for their own personal gain or for the protection of mankind. Some are rival organizations, some are splinter groups of the Foundation, and some are trusted associates of the Foundation. In any case, it has been deemed necessary to create and distribute a brief on what agencies the Foundation knows about and or stands towards them. Mana Charitable Foundation Overview Established in 1971 as an interfaith humanitarian relief agency, recovered documents describe the Mana Charitable Foundation's mission as sharing all of God's miracles with the least of his children, funded indirectly through associations with various charitable groups and religious organizations. And on occasion, publicly endorsed by wealthy philanthropists or academic institutions, the MCF's primary agenda since its founding has been the free distribution of anomalous objects or their byproducts to civilians living in poverty-stricken regions in the Third World or in areas afflicted by warfare, famine, or natural disaster. The MCF is currently recognized as a non-governmental organization by the United Nations and is known to operate legally and illegally in several hostile or isolated regions outside of the Foundation's sphere of influence. While no SCB objects known to have been distributed by the MCF to date have caused intentional harmed human beings or communities, and detained MCF operatives tend to demonstrate strong pacifist beliefs, containment breaches associated with the group have often resulted in human casualties, or severe threats to the global status quo due to unforeseen consequences of the object's release from containment, and or a zeal to distribute potentially helpful objects immediately without rigorous scientific study of their long-term behavior. Marshall Carter and Dark Limited Overview A club based in London, England, catering to the super-rich and with extensive political and financial ties worldwide, this group has caused extensive problems for the Foundation. Marshall Carter and Dark Limited is known for collecting rare and obscure items along with providing its members the most exclusive, expensive and rare experiences available. These activities resulted in conflict with the Foundation on numerous occasions. The group is not known for the use of force, as they prefer to apply extreme financial and political pressure to achieve their goals. When forced to use more direct means, Marshall Carter and Dark Limited employs outside agents and it is very difficult to connect said agents to the organization. Marshall Carter and Dark Limited has caused several SCP containment breaches, primarily through the use of money or social pressure. Several reports, records and even items have been leaked by Foundation personnel who had been approached with large amounts of money or threats of extensive jail time or torture. Notably, two containment sites were almost brought to public attention after the Foundation refused access to members of Marshall Carter and Dark Limited. In pertaining to Marshall Carter and Dark Limited, such as the name of the director or even a list of members, has proven very difficult to acquire. Agents encountering members of this group are advised to maintain a cover story and not, for any reason, reveal Foundation ties or SCP information. Nobody Overview Little is known about the person, entity or group known as Nobody. First cited in 1954, they have had numerous appearances since. There has only been one person seen at any given time, typically described as a male Caucasian dressed in a gray suit and a fedora. If asked his identity, he replies that he is Nobody. However, it is not known if this is the work of a single person or multiple agents of a single unknown agency. Their agenda is currently unknown, sometimes helping the Foundation, sometimes hindering it. Caution is recommended if any field agents encounter an operative identifying themselves as Nobody. End of file. To learn more about the SCP Foundation, subscribe to SCP Orientation Today and turn the notification bell on so you don't miss any of our videos.


In order to enable BitLocker Encryption, open Control Panel, BitLocker Drive Encryption. In the opening BitLocker Drive Encryption window, you will see all removable and non-removable data storage devices connected to this PC. There are two encryption types available for logical partitions. It allows encrypting any built-in non-removable disks system or not. The other type is for encrypting removable or external devices. Let's enable BitLocker in 4DSD. In the window that opens, you have to select how to unlock the disk. The next step in enabling BitLocker is to set up and backup a recovery key in case the main password is lost. I choose Save to a file. After BitLocker is turned on, it will automatically encrypt new files as they are created or modified.