3-22. CONTROL VALVE ASSEMBLY MAINTENANCE (CONT)
THEORY OF OPERATION (CONT)
Circuit Relief Valve.
In this example, loader frame is being raised and front edge
of the bucket is under a rock that will not move. Bucket spool is in neutral.
Front of bucket is held in position by the rock. As the loader frame rises, forces
are applied on bucket to extend bucket cylinders (dump bucket). With bucket spool in
neutral, these forces cause pressure at bucket spool B port to rise rapidly.
When pressure in bucket spool B port reaches circuit relief valve pressure setting,
the circuit relief valve poppet is pushed off its seat and bucket cylinders extend.
Oil flows through the seat and into return passages. Oil in the return passages
flows to the outlet port and to the reservoir.
The circuit relief valve will stay open as long as the piston rods in the bucket
cylinders are made to move with the bucket spool in neutral.
The circuit relief valve at bucket spool B port was used in this example. The other
circuit relief valves in control valve assembly will work the same way.