Pressure Limiter And High Pressure Relief Valves; System Check Valves; Bypass Valves - Danfoss 90 Series Service Manual

Service Manual
Operation

Pressure limiter and high pressure relief valves

System check valves

Bypass valves

12
Series 90 Pumps
Multi-function valve
High pressure
Pressure limiter housing
relief / check
valve poppet
Pressure limiter
lock nut
Pressure limiter
adjustment screw
Bypass
actuator
Pressure limiter
valve poppet
Some multi-function valves do not include a pressure limiter valve
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
To control
Multi-function valve
Servo piston
Port "A"
Servo Pres.
Relief Valve
Port "B"
Servo piston
Multi-function valve
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.
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.
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.
520L0818 • Rev 0101 • August 2015
Check valve
poppet
Bypass
P104 122E
Bypass
adjustment
Charge
pressure
relief valve
P104 123E