Troubleshooting a Wanner Hydra-Cell Pro^® Pump

Common causes for poor pump performance

Wanner Hydra-Cell Pro^® pumps are sealless positive-displacement pumps and they run for years when they are set up correctly. When flow or pressure is off, the notes below will usually get you back to full output.

Context Matters

An existing system that used to run well is not the same problem as a brand-new install. On a pump that once performed, start with the pump and the pressure regulating valve. On a new install, look at the inlet first.

Troubleshooting an Existing Application

routine maintenance consists of oil changes and fluid-end parts — mainly the check valves. The only parts in the process fluid are a pair of check valves per pump chamber plus the elastomers (diaphragms and O-rings). Aggressive chemistry can damage elastomers. Diaphragms and O-rings generally do not wear out with abrasive slurry. We pump TiO₂, lime, carbon slurry and ceramic slip with little effect on those elastomers.

Check Valve Components

The usual existing-system complaint is a pump that runs rough — pulsing flow or pressure, and less output than it used to have. A Hydra-Cell Pro displaces a fixed volume. Pressure is whatever resistance that volume meets. Worn check valves are less efficient and some of the discharge slugs back into the inlet. A gauge that used to sit still now swings. Most often the valve and seat have worn at the contact face after many hours. Reclaimed machine-tool coolant at high pressure will wear-out standard SS check valves within 6,500+ hours. The material if used with lime slurry for  flue-gas conditioning may last only 1,000 hours, thus ceramic and tungsten carbide materials are used for longer wear life.

The rest of the stack is the spring, spring retainer, O-ring, gasket and sometimes a dampening washer. Those pieces do not usually wear out on their own. Upset conditions can damage them. Fluid over 150°F can deform non-alloy dampening washers or retainers. A pump left running on badly worn valves can break a spring or retainer because those parts start to rattle. Anything that keeps a check valve from opening, closing and sealing reduces flow and pressure.

A check-valve kit replaces the whole stack. No special tools required. Most models take about an hour to swap out the check valves, and you can do it in place if there is room.

Skipped oil changes wear the hydraulic end — the parts that are not designed to see process fluid. Interval depends on model and pressure. 4,000 to 6,000 hours is typical. When we look at an existing pump we start with the oil:

• Process fluid mixed in (that points to a torn diaphragm)
• Level is low (oil left through a diaphragm, housing or vent cap)
• Has a heavy silver sheen, worn meal bits (hydraulic-end wear that requires experienced service technitions). A few silvery specks are normal. Worn oil should look uniformly black.

If the oil looks right and the pump ran well for a long stretch, a valve kit or a full overhaul kit (elastomers included) plus fresh oil usually returns it to original performance. If you see damage from an upset, look at materials and process control before you just replace parts.

Elastomers fail from chemistry, temperature, over-pressure, or — rarely — a sharp object stuck in a chamber. An inlet check jammed open with trash looks like a worn valve. How long the pump ran well before it it began to run rough may infer wear vs. upset condition.

We have had customers let water freeze in the head, cracked the housing, then tried to run with ice in the chambers and ruined the diaphragms.  The ice melts and you need to use the damaged components as clues.

Troubleshooting New Applications

Every Hydra-Cell Pro is factory tested at full flow and pressure. A new pump that will not discharge the rated flow or pressure is a problem almost always related to  an inlet problem. Displacement is fixed and the valves, elastomers and oil are new, so when the output is low its an indication that the pump is starved for liquid. Hydra-Cell Pro pumps will self-prime and they have some lift, but piping can still leave NPSHa below NPSHr. Each IOM manual has NPSHr curves and the formulas for NPSHa.

Typical plumbing faults: undersized tank, undersized suction pipe, a dirty filter, and air in the liquid from how the tank is filled or how the regulating-valve bypass is piped. A system that is quiet on a full tank and rough on a low tank is a common clue. Pressurized feed can still aerate if velocity is high and nearby elbows stir create turbulence at the inlet.

Put a compound gauge on the inlet and a liquid-filled gauge on the discharge. That tells you quickly whether the pump has positive suction and whether flow is steady. Another check: route the discharge and measure flow into a bucket. If it is low, the pump is starving. You will hear cavitation. That is an inlet problem.

Low or No Pressure

Pressure is restriction to flow. If the inlet is good and pressure is still low, look at:

• Shaft RPM — wrong belt/pulley set or the motor wired incorrectly
• Outlet restriction too large for the flow you have — worn spray nozzles, a tool, a seal flush. Flow rates in nozzle catalogs can be ±10%. If the pumps maximum flow rate is too little to create the desired back pressure you will need to either use a larger pump or address the components in discharge line.
• Trash holding an inlet check open — PTFE tape, pipe dope, weld slag. Common on first start-up
• Air lock — compressible air or other gas in the pump chambers preventing enough liquid from entering. Reduce the discharge pressure for the first 30 seconds (pressure regulating valve loosened to the max) or use an air-bleed valve on the discharge until the chambers fill.

Don’t Forget the Pressure Regulating Valve

Low pressure is sometimes caused by the pressure regulating valve — set wrong, or the valve and seat are worn. The plunger and valve seat last longer than the pump check valves, but they do wear. Wear opens an invisible leak to bypass, so less flow goes to the process and pressure drops. That drop is usually steady, not pulsing, and it comes on slowly. Operators keep cranking the adjusting screw until there is no more adjustment. On a system that used to hold pressure, look at the valve as well as the pump.

 

Related Articles

• Hydra-Cell pump installation guidelines
• Check valve wear insights
• Analyzing diaphragm damage
• Hydra-Oil design and change intervals
• Repair kit contents
• How to repair Hydra-Cell pumps
• Sealless pressure regulating valves

Wanner™ is a trademark and Hydra-Cell^® is a registered trademark of Wanner Engineering, Inc.