Parker’s three way pilot operated spool valves are used to direct flow alternately from either side of a closed loop transmission for cooling or filtering. With flow ranging from 10 gpm to 24 gpm, and pressures up to 5000 psi, these valves are a versatile solution to many hydrostatic applications. Parker’s N04A4 and N04B4 are higher flow versions of the DH103B and DH103C valves. The N04A4 series operation in its neutral (deactivated) position allow Port 3 to be open to Port 4, with Port 2 blocked. When a pilot signal is activated at Port 1, the spool shifts against the spring allowing Port 3 to be open to Port 2, with Port 4 blocked. The spring chamber is vented to Port 4 so care needs to be taken with back pressure at Port 4 additive to the spring setting. Parker’s N04B4 series operation in its neutral (deactivated) position allows Port 3 to be open to Port 2, with Port 4 blocked. When a pilot signal is activated at Port 1, the spool shifts against the spring allowing Port 3 to be open to Port 4, blocking Port 2. The spring chamber is vented to Port 4 so care needs to be taken with back pressure at Port 4 additive to the spring setting. Parker’s N04 series of Pilot Operated Directional Valves are available with switching pressures of 73 psi and 145 psi.