Some multi-function valves do not include a pressure limiter valve
Pressure limiter and high pressure relief valves
Series 90 pumps have a sequenced pressure limiting system and high pressure relief valves. When the
system pressure reaches the preset, the pressure limiter system rapidly de-strokes the pump to limit
system pressure. For unusually rapid load application, the high pressure relief valve immediately limits
system pressure by cross-porting system flow. The pressure limiter valve acts as the pilot for the high
pressure relief valve spool. The high pressure relief valve is sequenced to operate at approximately 35 bar
(500 psi) above the level that initiates the pressure limiter valve.
Circuit diagram showing pressure control mechanism
For some applications, such as dual path vehicles, the pressure limiter function may be defeated so that
only the high pressure relief valve function remains.
System check valves
The system check valves allow pressurized flow from the charge pump to enter the low pressure side of
the loop. This is needed as the pump generally loses system pressure due to lubrication/cooling flow and
other factors. Since the pump operates in either direction, the system uses two check valves to direct the
charge supply into the low pressure lines. The system check valves are part of the multi-function valve
assembly.
Bypass valves
You can operate the bypass valves to move the vehicle or mechanical function when the pump is not
running. Manually resetting the valve position opens the valve. The bypass valves are built into the multi-
function valves.
Service Manual
Series 90 Pumps
Operation
12 520L0818 • Rev 0101 • August 2015
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