Warning
Remote filter heads without bypass and poor plumbing design can encounter excessive pressure drops
that can lead to charge pump damage in addition to contaminants being forced through the filter media
and into the transmission loop.
Fluid Selection
Ratings and performance data are based on operating with hydraulic fluids containing oxidation, rust
and foam inhibitors. These fluids must possess good thermal and hydrolytic stability to prevent wear,
erosion, and corrosion of pump components.
Never mix hydraulic fluids of different types.
Reservoir
The hydrostatic system reservoir should accommodate maximum volume changes during all system
operating modes and promote de-aeration of the fluid as it passes through the tank. A suggested
minimum total reservoir volume is 5⁄8 of the maximum charge pump flow per minute with a minimum
fluid volume equal to ½ of the maximum charge pump flow per minute. This allows 30 seconds fluid
dwell for removing entrained air at the maximum return flow. This is usually adequate to allow for a
closed reservoir (no breather) in most applications.
Locate the reservoir outlet (charge pump inlet) above the bottom of the reservoir to take advantage of
gravity separation and prevent large foreign particles from entering the charge inlet line. A 100-125 μm
screen over the outlet port is recommended. Position the reservoir inlet (fluid return) to discharge below
the normal fluid level, toward the interior of the tank. A baffle (or baffles) will further promote de-aeration
and reduce surging of the fluid.
Case Drain
All single S90 pumps are equipped with multiple drain ports. Port selection and case drain routing must
enable the pump housing to maintain a volume of oil not less than half full and normal operating case
pressure limits of the unit are maintained. Case drain routing and design must consider unit case pressure
ratings.
A case drain line must be connected to one of the case outlets to return internal leakage to the system
reservoir.
Technical Information
Series 90 Axial Piston Pumps
System Design Parameters
520L0603 • Rev 0804 • March 2016 15
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