FILLER CAP
AND
AIR FILTER
CABLE
STRAINER
COVER
OVERFILL
SELECTOR
AND
VALVE
STORAGE
DRAIN
COVER
GASKET
RESERVOIR
SELECTOR
VALVE
COVER
ASf08006
LIQUID
LEVEL
DRAIN
GAUGE
Figure 8-6.--Hydraulic Reservoir Assembly A/M27T-5.
outlet port in a given period of time at a given speed.
decreases. This drop in the volume of output is the
Volume of output is usually expressed in gallons per
result of an increase in the amount of internal leakage
minute (gpm). Since changes in pump speed affect the
from the outlet side to the inlet side of the pump. This
volume of output, some pumps are rated according to
leakage is called pump slippage, and is a factor that
displacement. Pump displacement is the amount
must be considered. For this reason, most pumps are
(volume) of fluid the pump can deliver per cycle. Since
rated in terms of volume of output at a given pressure.
most pumps use a rotary drive, the displacement is at
The amount of internal slippage in a pump is an
t i m e s ex p r e s s e d i n t e r m s o f c u b i c i n ch e s p e r
indication of its efficiency, and is usually expressed as
revolution.
a percentage.
A pump does not create pressure. However, the
Fixed displacement pumps deliver a definite
pressure developed by the restriction in the system is a
volume of fluid for each cycle of pump operation,
factor that affects the volume of output of the pump. As
regardless of the resistance offered. The output volume
the system pressure increases, the volume of output
can be changed only by changing the speed of the
8-7
