Sealless Wanner™ Hydra-Cell^® Pro Pump vs.
External Gear Pump for Metering Applications

The difficult-liquids article covered why a Hydra-Cell^® Pro lasts on fluids that other PD pumps do not like. This one is a closer look at metering: a P400 Hydra-Cell Pro against a Zenith C-9000 external gear pump (the C-9000 series built for corrosive and poor-lubricating fluids). Flow and pressure bands overlap, so both get quoted on the same jobs.

Positive-displacement pumps move a fixed volume per shaft turn and will run above 1,000 PSIG. What sets the Hydra-Cell Pro apart is that nothing rubbing in the process liquid is a dynamic seal.

Rated flow and pressure are similar. The P400 has a wider material list, but that is not the main point. The static diaphragm seal is what cuts leak paths and unplanned stops compared with a packed or sealed gear pump.

Comparison of the Designs

A Hydra-Cell Pro head is a manifold plus a valve plate. The manifold has one inlet and one outlet on the outside and, on the inside, passages to each chamber. Frames have one, three or five chambers. The P400 has three. Liquid enters, splits to the three chambers, and leaves through a common outlet.

The valve plate holds the inlet and outlet check valves on the manifold side. The other side clamps to the body and forms the chambers. Shaft rotation grows and shrinks chamber volume. The check valves set direction.

An external gear pump has ports 180° apart (in-line) and a pair of rotating gears. Liquid is trapped between gear and casing and carried to the outlet. Meshing teeth set direction.

A gear pump has fewer parts overall. A Hydra-Cell Pro has fewer parts in the liquid.

A gear pump puts intermeshing gears, drive and arbor shafts, sleeve bearings and spacer bushings in the process. A Hydra-Cell Pro puts only check valves and elastomers in the process.

Those valves and elastomers come in a wide set of alloys and non-metals. A gear set is boxed in by what the teeth, bushings and case can be made from.

Intermeshing Gears vs. Check Valves

Metering means a fixed volume per turn. The Hydra-Cell Pro exceeds API 675 performance. Wear is the disc-to-seat face, and it is gradual. Harder or more compatible alloys and ceramics stretch that life.

A gear pump gets that accuracy by running the teeth very close. Gear, case and sleeve-bushing wear show up in the rate. The shaft is sealed with a mechanical seal. All of those faces take abrasive wear, so Zenith wants 5 micron absolute filtration. That is a Beta 5000 cartridge and a housing built for it — see Understanding Retention Efficiencies for Filter Cartridges.

The P400 will pass solids to 500 microns. Nominal-rated media is enough.

Those meshing gears live on the process liquid for lubrication and cooling. The maker says do not run dry. Even for self-prime they want the head filled first.

A Hydra-Cell Pro has no dynamic seal in the liquid, so it will run dry and it will self-prime. A plugged inlet filter that cavitates a gear pump ruins the teeth. The same event does not take out a Hydra-Cell Pro.

Viscosity and Efficiency

Thin liquid slips through gear-to-case and gear-to-gear clearances, so volumetric efficiency falls. The usual advice is to oversize the gear pump and turn it slower.

Viscosity barely moves Hydra-Cell Pro efficiency. The check valves are light, spring-loaded and fast.

The Application Matters

Similar flow and pressure do not mean similar machines. If the gear pump is living on expensive filters or annual tear-downs, look at a Hydra-Cell Pro.

A Hydra-Cell Pro will meter viscous, water-like, abrasive and shear-sensitive liquid. Filtration is coarser than most other PD pumps — a cost that belongs to the pump choice, not to the process.

Cost

Online list pricing from 2016 put a P400 at half the price of a Zenith C-9000 in the same band.

Zenith wear-part cost is not published here. A P400 service is two quarts of synthetic oil and up to two valve kits — about $600 in 2022. Valves come out with ordinary tools and no factory school.

The Zenith IOM wants plastic tools and no force; tolerances are that tight. Silicon-carbide sleeve bearings are an interference fit from the factory. They tell the customer not to pull them:

“These sleeve bearings are extremely brittle and fragile, and can be easily broken resulting in multiple part damage and high replacement cost.”

Most of the work these two pumps do does not overlap. Where it does — a gear pump that is always in the shop — the Hydra-Cell Pro is the one to price.

Related Articles

• Hydra-Cell Pro vs mag-drive gear pumps
• Pumping difficult liquids
• Hydra-Cell Pro vs AODD
• Hydra-Cell Pro vs piston and plunger pumps
• P400 metering pump
• Metering pump overview