Cuts in at specified psi and out at specified psi. Has hand toggle unloader and discharges pump air through felt muffler. For pumps without head unloaders. 3/8" MPT x 1/8" FPT for throttle control and 1/8" FPT for check valve port. Factory preset, yet can be adjusted for higher or lower pressures. For compressors that have check valves. Cuts in at 105psi and out at 135psi.