KB21 Service Manual Pub 09-14
39
sSection 30
Boom Control Circuits
the boom mowers.
Open center valves are normally controlled by either cable controls or integrally mounted handles. They
may, however, also be controlled with an electronic joystick controller if ordered as an option.
Open Center Valves.
Control valves in an open center circuit utilize a port through the center of the valve which, when the
valve spools are in neutral, provides a passage directly to tank. These valves are most commonly used
valve at all times when the pump is turning (or when the tractor engine is running).
the valve until one of the spools in the valve is moved to allow some of the oil to be diverted to a cylinder
to perform work.
The performance or speed of a valve is a function of four characteristics of the load:
1. Weight
2. Pump Flow (or engine speed)
3. The Direction of the work (up or down)
4. Any other function used simultaneously
The Speed in which the handle is moved has no clear cut relationship to speed of the cylinder
movement.
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