FLUID MOTOR CONTROL CIRCUIT WITH FAST-ACTING QUICK-DROP VALVE

摘要

FLUID MOTOR CONTROL CIRCUIT WITH FAST-ACTING QUICK-DROP VALVE A control circuit for a fluid pressure-operated cylinder or the like has a quick-drop valve which enables faster gravity-assisted lowering of a load and which quickly shifts to a power-down mode of operation when dropping of the load by gravity ceases. Means sensing flow rate to the head end of the cylinder and sensing cavitation in the head end initiate the quick-drop operation at which the discharge path from the cylinder back to tank is totally blocked and all discharge from the rod end is recirculated to the head end. When resistance to further lowering of the load occurs, the quick-drop valve responds by shifting to block communication between ends of the cylinder while establishing a rod end discharge path to tank to initiate a power-down mode of operation quickly and without lag or bounce.