Lockable apparatus for deactivating a hydraulic system

A lockable apparatus for diverting pressurized hydraulic fluid from a pump output conduit of a vehicle used in earth moving operations to a hydraulic system reservoir to disable hydraulically operated components of the vehicle to prevent unauthorized vehicle operation, said appartus comprising,

• a valve body including fluid inlet and outlet ports and a reservoir return port, a spring biased valve spool having front and rear faces and defining an orifice extending therebetween, said spool faces responsive to fluid pressures with the spool having a first position whereat the spool opens said reservoir return port for fluid passage through said return port to prevent hydraulic component operation and a second position whereat said reservoir return port is closed for directing pressurized hydraulic fluid to said outlet port for normal hydraulic component operation, means urging said spool to a reservoir return port closing position, check valve means in upstream fluid communication with an area partially defined by one face of said spool and in downstream communication with the system reservoir whereby closure of the check valve will cause fluid pressure increase on said one face which pressure in conjunction with said urging means relocates said spool to close said reservoir return port for normal operation of the hydraulic system components, and
• check valve control means mounted on said valve body and having a first position opening the check valve to cause positioning of said spool to open the reservoir return port to divert fluid to the system reservoir to prevent operation of system hydraulic components, said control means having a second position to close the check valve to cause repositioning of said spool and closure of said return port for normal system component operation, said check valve control means including a lock on the valve body and having a plunger acting on said check valve means and enabling locking of same in said first or second position.