The HSUCO valve is primarily a pilot valve used to control large flow HSU, HSUO, or HSP valves.

Pilot pressures must be connected to port 1 to operate the integral relief valve to connect port 2 to 3 or port 4 to 3. Port 1 pressure is ported thru orifices in the center of the valve to the pilot relief valve (in the upper portion of the body). When the pressure exceeds this valve setting, pressure on the top side of the main spool is relieved. A pressure imbalance then exists across the main spool, and the port 1 pressure raises the main spool, blocking port 2 and allowing floe from port 4 to 3. When the pilot pressure (port 1) decreases, the pilot relief valve blocks flow. Pressure across the main spool is balanced, and the spring returns the main spool to block port 4 and connect port 2 to 3 again.

Several pressure ranges are available to choose from. The cartridge is constructed of steel parts, and operating parts are hardened and ground as required. The cartridge is designed for easy service or field repair.