Servo Pressure
Servo pressure is the pressure in the servo system needed to position and hold the pump on stroke. It
depends on system pressure and speed. At minimum servo pressure the pump will run at reduced stroke
depending on speed and pressure.
Minimum servo pressure at corner power holds the pump on full stroke at max speed and max
pressure.
Maximum servo pressure is the highest pressure typically given by the charge pressure setting.
Charge Pressure
An internal charge relief valve regulates charge pressure. Charge pressure supplies the control with
pressure to operate the swashplate and to maintain a minimum pressure in the low side of the
transmission loop.
The charge pressure setting listed in the order code is the set pressure of the charge relief valve with the
pump in neutral, operating at 1800 min
-1
(rpm), and with a fluid viscosity of 32 mm
2
/s [150 SUS].
Pumps configured with no charge pump (external charge supply) are set with a charge flow of 30 l/min
[7.93 US gal/min] and a fluid viscosity of 32 mm
2
/s [150 SUS].
The charge pressure setting is referenced to case pressure. Charge pressure is the differential pressure
above case pressure.
Minimum
charge
pressure
is the lowest pressure allowed to maintain a safe working condition in the low side of
the loop. Minimum control pressure requirements are a function of speed, pressure,
and swashplate angle, and may be higher than the minimum charge pressure shown
in the Operating parameters tables.
Maximum
charge
pressure
is the highest charge pressure allowed by the charge relief adjustment, and which
provides normal component life. Elevated charge pressure can be used as a
secondary means to reduce the swashplate response time.
Charge Pump Inlet Pressure
At normal operating temperature charge inlet pressure must not fall below rated charge inlet pressure
(vacuum).
Minimum charge inlet
pressure
is only allowed at cold start conditions. In some applications it is
recommended to warm up the fluid (e.g. in the tank) before starting the
engine and then run the engine at limited speed.
Maximum charge inlet
pressure
may be applied continuously.
Case Pressure
Under normal operating conditions, the rated case pressure must not be exceeded. During cold start case
pressure must be kept below maximum intermittent case pressure. Size drain plumbing accordingly.
The auxiliary pad cavity of axial pumps configured without integral charge pumps is referenced to case
pressure. Units with integral charge pumps have auxiliary mounting pad cavities referenced to charge
inlet (vacuum).
Possible component damage or leakage.
Operation with case pressure in excess of stated limits may damage seals, gaskets, and/or housings,
causing external leakage. Performance may also be affected since charge and system pressure are
additive to case pressure.
Service Manual
H1P 069—H1P 250 Axial Piston Single Pumps
Operating Parameters
20 |
©
Danfoss | September 2020
AX152886482551en-000504
