A Guide To Coupling The Right Hydraulic Hose Port Fittings

To construct or repair an enduring, non-leaking hydraulic hose, the correct ports and connectors have to be matched.

The accurate identification of the port fittings in the fluid power piping system is important for the selection and installation of hoses or tubes from one moving part to another.  Also, if repairing hoses and connectors, accurate identification is applicable for the same reasons.  Attempting to couple connectors and ports with different thread configurations will cause thread binding which will make the fitting and the port unusable.

The three tools that will help identify the correct connector for a port are calipers, a thread pitch gauge, and a seat angle gauge.

I.D./O.D. Calipers

These calipers measure the inside diameter (I.D.) threads of a female thread and the outside diameter (O.D.) of male threads.

The term “female threads” means the threads are on the inside of a socket-like port or connector post.  The term “male threads” means the threads are on the outside of the port or connector post.  When taking this measurement, make sure it’s the diameter of the largest point.

Calipers can also determine whether the threads are straight or tapered.

Thread Gauge

When the thread gauge is used, this determines how many threads per inch or millimeter are on or in the coupling post.  When placing the gauge against the threads, comparing the two against a lighted background will help arrive at a more accurate measurement.

Seat Angle Gauge

There are three types of hydraulic fitting sealing methods that are used to prevent leaks when the fittings are coupled together.

Mated Angle Fittings

One type is the mated angle fittings.  When two couplings are mated together, the threads are not what forms the seal to prevent leaks.  What forms the seal is when the two mating angle seats are joined together.  If the two angles do not match, leaks will occur.

The seat angle gauge tool measures the mating angle seat of the fitting.  Examples of mated angle connectors are the SAE 45° which is commonly used in refrigeration, automotive, and trucking piping systems, or the JIC 37° which is very common in fluid power systems.

The two other types of sealing methods are the O-Ring and tapered threads.  No measurement is required for these methods.

Tapered Thread Fittings

The tapered thread method forms a seal against leaks when the male and female fittings are threaded together, deforming the tapered threads, and applying pressure on the fittings which forms the seal.

These tapered thread connectors, the National Pipe Tapered Fuel (NPTF) connectors are widely used in fluid power systems but the National Fluid Power Association (NFPA) does not recommend the use of the NPTF connectors in hydraulic applications.

The NFPA established in 1953, is an organization that focuses on fluid power technology.  They educate the fluid power workforce and establish recommendations on how to construct or repair long-lasting hydraulic fluid hoses, based on the vast collective knowledge of the membership.

O-Ring Seal Fittings

In the three types of O-Ring seal methods, the O-Ring Boss (ORB), the flat face O-Ring seal, and the O-Ring flange, the O-Ring is what creates the seal.

What the NFPA does recommend for optimum control of leakage in medium and high-pressure hydraulic systems is the Straight Thread O-Ring Boss (ORB).

The ORB is the equivalent of the JIC 37° except for the way they seal.  The consensus, though, is that the ORB offers the best leak-free connection.

But what if, after all this measuring, you find that you need a non-standard or non-manufactured hose fitting to fit your port.  Contact us for small-batch reproduction of unavailable fittings using your original parts.