Hyster D174, Service & Repair Manual

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1900 SRM 97 Hydraulic Gear Pump Repair
RELIEF VALVE
Some pumps have a relief valve installed in a car-
tridge or in a bore in the rear cover. See Figure 4.
Relief valves in the pump prevent the pressure in
the controlled flow system from increasing beyond
the specifications. The relief valve in the cartridge
has a poppet and spring, with the seat for the pop-
pet in the cartridge. The relief valve and flow control
valve on some pumps are installed in the same car-
tridge. Some of the relief valves that are installed in
the pumps are adjustable only with shims. Replace
the cartridge if the relief valve has a problem.
1. INPUT SHAFT
2. BEARING BLOCKS
3. REAR COVER
4. DRIVE GEAR
5. CARTRIDGE, FLOW CONTROL AND RELIEF
VALVE
6. DRIVEN GEAR
7. FRONT COVER
Figure 4. Gear Pump Basic Parts
Hydraulic Gear Pump Repair
NOTE: Worn or damaged seals are the most common
cause of pump failure. The pump bearings, gears,
and shafts also wear. Many service persons do not
repair a worn pump because the cost of repairs can
be greater than the cost of a new pump. The seals
can be replaced in the hydraulic pump. If the pump
will be rebuilt, the following general procedures are
for repairing gear pumps.
REMOVE
WARNING
Make sure the carriage is lowered before dis-
connecting any parts of the hydraulic system.
1. If the lift truck is equipped with a valve on the
tank, the valve must be closed before removing
the pump. If there is no valve on the tank, re-
move breather and install a plug. This action
prevents the tank from draining too fast when
the inlet line is disconnected.
2. Disconnect hoses from pump. Put caps on all fit-
tings. Be careful so inlet hose is not damaged
during removal.
3. If the pump is driven by a drive shaft, disconnect
drive shaft at pump.
WARNING
Some of the hydraulic pumps are very heavy.
Use a lifting device when removing or in-
stalling the pump.
4. Remove capscrews holding pump housing to the
mount.
5. Remove pump from lift truck.
3