PROALL P Series, Service Manual, Page: 19 / 118

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
The mix auger section has additional work port anti-shock
and anti-cavitation valves. These valves prevent over
pressure spikes and cavitation protection when auger is
turned off at high speed.
5.3.4 CHARGE
IMPORTANT!
The charge circuit is powered by the last pump , which is a simple fixed displacement gear pump. The charge
pump circuit is only used to make up leakage in the returning oil from the system as well as to provide a positive
(supercharged) inlet pressure to the two main load sensing piston pumps. The other benefit is the addition of
continuous cooling flow even when the mixer is idle with PTO still on.

Charge pressure should be about 15psi (1bar) when the
mixer is at standby and nothing is running. As the functions
are turned on this pressure will drop by as much as half the
standby pressure. This is normal as the charge pump makes
up for system leakage through drain connections back to
the reservoir.

The main return filter housing has special valving inside
that ensures there is a positive pressure feeding the piston
pumps. The most important of these valves is the back
pressure or charge relief valve. Any oil not being feed back
to the inlet of the piston pumps must pass across this back-
pressure valve before entering the reservoir.

If the charge pressure is significantly below 15psi (1bar) at
standby, then the issue is either a faulty back pressure valve
in the filter housing or there is a drain connection that is
allowing charge oil to go directly back to tank.

The only valve in the hydraulic system that has a direct
connection back to the reservoir from the drain is the chain
oiler pressure reducing valve . If this valve is faulty or
A
A
B
C
B
B