KB21 Service Manual Pub 09-14
56
40-A. Bucher L.8S Manual Control/Cable
Control Circuit Main Relief Valve Operation
The control circuit is protected from over pressurization with the use of the Main Pressure Relief Valve
located in the inlet port of the Control Valve Assembly. (Shown below)
Those sections of the control valve assembly which utilize Work Port Relief’s will relieve pressure at
the work port setting. The Main Relief is usually set slightly higher than the work port relief’s and will
protect the entire circuit (rather than an individual section) from the possibility of damage due to over
pressurization.
Pressure in excess of the set pressure of the main relief spring will overcome the spring tension
and unseat the piston. This allows the pressurized oil to travel directly to tank. Once pressure is reduced
tank.
pressure setting. All control valve main relief’s for the KB21 mowers are factory pre-set at 2500
Setting can cause serious damage to system from over heating to excessive pressure damage.
Main relief pressure can be checked by installing a pressure gauge (at least 6000-PSI Gauge
recommended) in the pressure inlet line to the control valve. Pressure in excess of 3000PSI will cause
. Adjustment to the
main relief is not recommended.
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