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2)
PRINCIPLE OF OPERATION
(1)
Mechanism for delivering oil
The drawing at right shows the
operational principle of an external gear
pump in which two gears are rotating in
mesh.
The oil entering through the suction port is
Suction
Discharge
trapped in the space between two gear
teeth, and is delivered to the discharge
port as the gear rotates.
Except for the oil at the bottom of the gear
teeth, the oil trapped between the gear
teeth, is prevented from returning to the
suction side with the gears in mesh.
Since the gears are constantly delivering
oil, the oil delivered to the discharge port
is forced out of the port.
The amount of discharge increases with
the speed of rotation of the gear.
If there is no resistance in the oil passage
into which the discharged oil flows, the oil
merely flows through the passage,
producing no increase in pressure.
If however, the oil passage is blocked with
something like a hydraulic cylinder, there
will be no other place for the oil to flow, so
the oil pressure will rise. But the pressure
which rises in this way will never go
higher, once the hydraulic cylinder piston
starts moving because of the oil pressure.
As described earlier, the pump produces
the oil flow, but not the oil pressure. We
can therefore conclude that pressure is a
consequence of load.
In other words, the pressure depends on
a counterpart.
(770-3ATM) 4-9
4-9
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