SERVICE REPAIR
H370C H420C H470C-36 H470C-48 [C008]
1
INTRODUCTION
DESCRIPTION
Gear pumps have several sections and are made with a
single set (single stage) of gears or with multiple sets
(tandem) of gears. A single stage pump has two covers
and the gear housing with the gears. Seals are used to
prevent leaks between the sections. Tandem pumps
have a gear housing for each set of gears. Most tandem
pumps also have a center section for the bearings. The
inlet and outlet ports are normally on the gear housing or
rear cover. The front cover has the seal for the input
shaft. The input shaft is connected to a driven sprocket,
coupling, or gear by splines or a key.
All the gear pumps have devices that keep the thrust
clearance at a minimum when the pressure increases.
When the pressure is low, the clearance increases to pre-
vent wear. To prevent leakage when the pressure is high,
the oil from the outlet side of the pump is transferred to a
wear plate. The oil pushes the wear plate against the
gears. Some pumps have bearing blocks that move
closer to the gears when the pressure increases.
OPERATION
Gear pumps have the teeth of the gears engaged in the
center of the pump. When the input shaft is turned, the
drive gear turns the driven gear. The oil in the inlet
chamber is moved out from the center by the teeth of ro-
tating gears. The oil between the teeth is moved around
the pumping chamber to the outlet chamber. The oil is
pushed from the outlet chamber by the gear teeth that are
beginning to engage.
FIGURE 1. TYPES OF GEAR PUMPS
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1. ONE–SECTION PUMP
2. DRIVE GEAR
3. TWO–SECTION PUMP
4. DRIVEN GEAR
1
2
2
3
4
4
2
1. INLET
2. OUTLET
3. SEAL MADE BY GEAR TEETH
FIGURE 2. OPERATION OF GEAR PUMP
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1
3
2
3
3
FIGURE 3. CHECK VALVE
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1. OIL ENTERS GROOVES IN BUSHINGS
2. OIL ENTERS INLET CHAMBER
2
1
FIGURE 4. BASIC PARTS OF A GEAR PUMP
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1. INPUT SHAFT
2. BEARING BLOCKS
3. REAR COVER
4. DRIVE GEAR
5. CARTRIDGE, FLOW CONTROL
AND RELIEF VALVE