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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 never to 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.
(2)
Internal oil leakage
Oil leaks from a place under higher pressure to
place under lower pressure, provided that a gap
or a clearance exists in between.
In the gear pump, small clearance are provided
between the gear and the case and between the
gear and the side plate to allow the oil to leak out
and to serve as a lubricant so that the pump will
be protected from seizure and binding.
The drawing shows how the leaked oil flows in
the pump. As such, there is always oil leakage in
the pump from the discharge side(under higher
pressure) to the suction side. The delivery of the
pump is reduced by an amount equal to the
pump discharge.
In addition, the delivery of the pump will also
decrease as the amount of oil leakage increase
because of expanded radial clearance resulting
from the wear of pump parts, the lower oil
viscosity resulting from increases on the oil
temperate, and the initial use of low viscosity oil.
Suction
Suction
6-13
Discharge
100D7PMP26
Discharge
100D7PMP27
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