
T415 Operation & Service Manual
68
Maintenance
9
Series 90
Functional Description
Charge Pump
The charge pump is necessary to supply cool fluid to the
system, to maintain positive pressure in the main system
loop, to provide pressure to operate the control system,
and to make up for internal leakage. Charge pressure
must be at its specified pressure under all conditions of
driving and braking to prevent damage to the transmis-
sion.
The charge pump is a fixed-displacement, gerotor type
pump installed in the variable displacement pump and
driven off the main pump shaft. Charge pressure is limited
by a relief valve.
The standard charge pump will be satisfactory for most
applications. However, if the charge pump sizes available
for the given main pump size are not adequate, a gear
pump may be mounted to the auxiliary mounting pad and
supply the required additional charge flow.
Charge Relief Valve
The charge relief valve on the pump serves to maintain
charge pressure at a designated level. A direct-acting
poppet valve relieves charge pressure whenever it sur-
passes a certain level. This level is nominally set refer-
encing case pressure at 1500 rpm. This nominal setting
assumes the pump is in neutral (zero flow); in forward or
reverse charge pressure will be lower. The charge relief
valve setting is specified on the model code of the pump.
Multi-Function Valves
The multi-function valve incorporates
the system check valve,
the pressure limiter valve,
the high pressure relief valve and
the bypass valve
in a replaceable cartridge.
These functions are described separately. There are two
multi-function valve cartridges in each Series 90 pump to
handle functions in either direction. See corresponding
Sections for adjustments and repairs.
NOTE: Some multi-function valves do not include a
pressure limiter valve.
PV with Charge Pump
90000243
Pump Charge System
90000804E
Pump Features
Multi-Function Valve
90000243
Case
Drain
Line
Charge Relief Valve
Charge
Pump
System
Check
Valves
Input
Inlet Filter
Tank
PV
PF