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

The difficult-liquids article covered why a Wanner 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 it doesn't have a dynamic seal.

Rated flow and pressure are similar. The P400 has a broader range of wetted materials, but its key advantage is not having a dynamic seal, which is a pathway to leakage and are expensive to repair.

Comparison of the Designs

A Hydra-Cell Pro pump head consists of 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. Hydra-Cell Pro pumps 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 of flow.

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 of flow.

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

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

Hydra-Cell Pro valves and elastomers come in a wide variety of alloys and non-metals. A gear pump is limited by the materials which the gears, bushings and case can be made from.

Intermeshing Gears vs. Check Valves

The Hydra-Cell Pro exceeds API 675 performance standards. Wear is limited to the check valve wear and it is gradual. Harder or more compatible alloys and ceramics can extend their wear life.

A gear pump gets its accuracy by running the teeth very close. Gear, case and sleeve-bushing wear reduce efficiency. The shaft is sealed with a mechanical seal. All of those interfaces are suseptable  to abrasive wear, thus Zenith recommends incorporating 5 micron absolute filtration. That is a Beta 5000 cartridge or bag filter (Understanding Retention Efficiencies for Filter Cartridges).

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

Those meshing gears depend upon the process liquid for lubrication and cooling. Zenith warns against running dry and even for self-priming pumps the recommend filling the pump head with liquid first.

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 affects 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 your gear pump requires expensive filters or annual tear-downs, consider a Hydra-Cell Pro.

A Hydra-Cell Pro will meter viscous, water-like, abrasive and shear-sensitive liquids. Filtration requirements are coarser than most other PD pumps — you can filter to the process and other components, not the pump.

Cost

Online list pricing from 2016 put a P400 at half the price of a Zenith C-9000 having similar flow and pressure capabilities.

Zeniths spare parts cost were not published at the time this page was written. A P400 service is two quarts of synthetic oil and 1 valve kit — about $700 in 2026. Valves are swapped out with ordinary tools and do not require special training.

The Zenith IOM specifies plastic tools and minimal 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.”

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