TM 5-3805-262-343-22. CONTROL VALVE ASSEMBLY MAINTENANCE (CONT)THEORY OF OPERATION (CONT)Circuit Relief Valve.In this example, loader frame is being raised and front edgeof 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, forcesare applied on bucket to extend bucket cylinders (dump bucket). With bucket spool inneutral, 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 passagesflows to the outlet port and to the reservoir.The circuit relief valve will stay open as long as the piston rods in the bucketcylinders 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 othercircuit relief valves in control valve assembly will work the same way.3-642
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