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Wanner Hydra-Cell Pro® Sealless Positive Displacement Pumps:
Check Valve Wear Insights
A Wanner Hydra-Cell Pro® pump has no dynamic seal, which is why it is so reliable pumping liquids that chew-up, seals, packing, gears and stators. The wear parts that do see the liquid are the check-valve assemblies — specifically the disc and seat.
Earlier articles covered design comparisons, repair, troubleshooting and oil. This one focuses on the liquid-end check valves.
The only parts in the process liquid are the check-valve stacks, the diaphragms and the O-rings. A stack is a seat, disc, spring, gasket and retainer.
The retainer compresses the gasket to seal the stack and preloads the spring so the disc sits on the seat. It also guides the spring. The machined disc helps keep that spring and disc centered. With compatible materials and no upset, wear happens at the disc-to-seat face.
Each pump chamber has a pair of valves in the valve plate — inlet path and outlet path — into common manifold channels. Every shaft revolution increase the volume of the chamber, then shrinks it. Shafts turns as high as 1,750 RPM, which is 1,750 check valve open and closes a minute.
Normal Valve / Seat Wear
The disc hits the seat resulting in impact wear. On liquid with few particles and using heat-treated stainless disc and seat, expect about 6,000 hours before the pump starts to run rough.
As the faces wear they stop sealing efficiently, the spring load drops and some of each discharge stroke leaks back to the inlet. The pump gets louder and discharge pressure swings with the changing displaced volume.
Wear is not linear. You can have 6,000 smooth hours, a few hundred hours of light roughness, then a hard drop. Critical applications requiring smoother flow and pressure can monitor for pressure or flow fluctuations to avoid unscheduled down time.
Chemistry that attacks the valve accelerates disc and seat wear and can also damage both the spring and retainer.
Hydra-Cell Pro pumps are used for reclaimed liquid and slurries: lime, ceramic slip for spray drying, airless paint, bentonite, waxy resins. These applications are tough on check valves, often oversizing the pump and using erosion resistant materials provide the best operational value. A valve kit can be installed within 1-2 hours without pulling the pump off the skid, and it costs less than the wear parts on most other PD designs.
Wear Forces on Disc and Seat
The stack is a light disc, not a solid ball, so it can keep up at full capacity.
Three things wear the faces:
- Impact — disc against seat, up to 29 times a second at 1,750 RPM, plus any hard particle caught between the two faces.
- Erosion — velocity through the opening and closing valve, and the hardness of particles sweeping across those faces.
- Stress — uniform pitting as the disc approaches the seat, a cavitation-like effect. You rarely see it by itself; it rides along with impact. Chemistry and extreme temperature add their own stress.
Ways to Extend Valve Life
On an existing pump the fastest gain is a harder or more compatible material. Standard is 17-4 heat-treated stainless. If 17-4 is in doubt chemically, try 316L, Nitronic 50 or Hastelloy C. For slurry or hard particles, ceramic and tungsten carbide take erosion better.
The best time to buy life is at sizing. A D10 outputs 8.8 GPM at 1,750 RPM. An H25 outputs 20 GPM at 1,200 RPM. Run that H25 at 506 RPM for the same 8.8 GPM and velocity through the valves drops — the H25 valves are physically larger — so erosion falls. The D10 has to turn about 3½ times as fast for that same flow.
Water and clean, water-like liquid can be pumped at higher RPMs.
Hardness is not the whole story. Ceramic can shatter if it is dropped or hit with a hard thermal shock. Alloys do not.