Wanner Hydra-Cell Pro^® Pumps Compared to Piston and Plunger Pumps

Comparison of pump designs with application examples

Piston and plunger pumps are reciprocating positive-displacement pumps. A Wanner Hydra-Cell Pro^® uses the same idea — chambers that grow and shrink — but it has no dynamic seal on the process liquid. That is the difference that matters. You can run coarser filtration, hotter or colder liquid, non-lubricating fluid, cavitation and shear-sensitive product without chewing up packing. Packing and seals are the weak point on piston and plunger pumps: they leak, they stop the line, and they cost money. Both of those designs seal the liquid the same way along the moving rod.

Comparison of the Designs

The drive end is similar. A swash plate or cam works several chambers in sequence. On a piston or plunger pump a cylinder moves in and out of the chamber. The outside of that rod has to be sealed so high-pressure liquid does not travel along it. Those seals are usually PTFE, PE, PEEK or nitrile, on both the liquid end and the hydraulic end. The process liquid is what lubricates them so the rod can slide.

That sliding face wears faster when you pump:

• reclaimed or abrasive liquid
• hot liquid
• dry (these pumps want to be primed)
• cavitating liquid from air or a tight suction line

Particles are the usual leak cause. They lodge between the rod and the seal and grind both. That is why plunger pumps often use ceramic plungers.

Piston and plunger pumps want at least 80 mesh (~177 micron) filtration. On reclaimed liquid, 50 micron and ≤50 PPM solids (~5%) is the usual recommendation if you want the packing to last. Dry running and high temperature are also hard on those seals because the process liquid is their only coolant and lubricant.

A Hydra-Cell Pro replaces the metal piston with synthetic motor oil. That hydraulic column moves a diaphragm in each chamber. The diaphragm is clamped between head and body — a static seal, not a rubbing stem seal. Particles, dry running, cavitation and extreme liquid temperature do not open a leak path. The packing leak path is gone.

The diaphragm has a built-in convolution. It rolls more than it flexes. Except for PTFE-encapsulated styles, diaphragms are not treated as a wear part. A customer called for a D10 fluid-end kit after 11 years and more than 20,000 hours on reclaimed machine-tool coolant at up to 1,000 PSIG. The check valves were worn. The diaphragms were not. They changed them anyway because the head was open. A diaphragm costs less than a plunger and rod.

Diaphragms last because they are hydraulically balanced — never more than about 2 PSI across the face. A nested check valve (the “Hydra-Cell”) behind each diaphragm keeps that balance. Press a sheet of tissue between your palms as hard as you want; the paper does not tear because both sides see the same load. That is the same idea.

Plunger pumps also have dynamic seals on the plunger rod. Those wear unless the liquid and hydraulic sides are kept apart.

The diaphragm can still fail if:

• the liquid attacks the elastomer
• the pump is run past MAWP
• a large hard particle (including ice) lodges in the chamber
• liquid temperature exceeds the elastomer limit

Where the Leakage Goes

When piston or plunger packing fails, oil or process liquid goes to the floor. Most of those pumps do not mix hydraulic oil with process liquid.

When a Hydra-Cell Pro diaphragm fails, the two sides can mix. Positive inlet pressure drives process liquid into the hydraulic end. Flooded suction or lift lets some oil into the process. For jobs that cannot accept that, Wanner^® supplies food-contact oil, ammonia-resistant oil and water-soluble oil.

The volume that can pass a torn diaphragm is small. Displacement drops as soon as the diaphragm is open. You hear chatter and see the gauge swing.

Oil-level monitors will trip a PLC when the level moves, which is how many plants catch a diaphragm on a sensitive liquid.

Flow Ranges

Piston pumps generally make more flow than plunger pumps and stay at lower pressure — piston rings do not like high pressure. Plunger pumps make higher pressure because the rod seal is built for it.

Hydra-Cell Pro pumps will go to 5,000 PSI. Most of the work we see is under 1,000 PSI. The sealless wet end is what puts the pump on liquids that would eat packing, and a lot of those jobs are metering, not high head.

Maintenance

Neither design is hard to work on. The difference is how often you do it, and what that costs in downtime.

Applications

High-pressure water, oilfield injection and atomizing spray are common to all three. A piston pump of similar size can make higher pressure than a Hydra-Cell Pro. The Hydra-Cell Pro will take corrosive and abrasive liquid without losing the packing and without losing rate. If you are changing seals and plungers on a schedule, that duty is a candidate.

Related Articles

• Pumping difficult liquids with Hydra-Cell Pro pumps
• Comparison to progressing cavity pumps
• Comparison to AODD pumps
• Hydra-Oil and oil-level monitors
• Analyzing diaphragm damage
• Hydra-Cell Pro design overview