
by Tony Carden, Tuthill Corporation
Inlet manifold check valve CFDFigure 3. Inlet manifold check valve CFD

Ideally, the maximum possible amount of fluid should be drawn into and pushed out of the fluid chambers with each stroke of the piston, while minimizing (or controlling) small amounts of hydrodynamic cavitation. The diaphragms must have the longest possible service life and be manufactured of many different materials that allow the pump to be used in a wide range of fluids.

Cavitation occurs when the pressure drops below the saturated vapor pressure of the liquid being pumped. Bubbles generate and implode when fluids are subjected to a decrease, then subsequent increase, in pressure. This causes high energy densities, temperatures and pressures to occur at the surface of the bubbles. Vaporization follows, and depending on the fluid being pumped, it even has the potential to freeze or explode.

Designing the fluid chamber, valves and diaphragms using a CFD virtual environment allows engineers to tweak the design to achieve the desired results without costly failed test units. Simulating flow also allows the engineers to see how each change affects the product’s operation.

When maximizing performance and efficiency, the larger the effective piston area, the larger the displacement of the fluid. The effective piston area is mid-point between the backup washer and the seal point of the diaphragm itself.

The engineers also wanted to maximize the diaphragm flex life and have the longest flex hinge possible. They accomplished this by creating a “booted” design, adding length to the convolute form (see Figure 4). The resulting increase in efficiency also helped mitigate cavitation and provided a more uniform fluid displacement, regardless of input pressure, to completely empty the fluid chamber.

Figure 4. A booted design added length to the convolute form and increased diaphragm flex life.

The search for efficiency is ongoing as engineers continuously seek ways to get more work from less energy. It is clear that as technology advances, so will this search for improved efficiency.