ZK7.1 GP K7 Flow Sensitive Unloader Valve 2.9-4.2 GPM @ 3500 PSI by General Pump. Eliminates high pressure in all lines while unit is in bypass mode. Maximun PSI 3500, Maximun Temp 165 deg F., 3/8 in. FNPT Inlet, 3/8″ MNPT Outlet, 3/8 in. FNPT By-Pass. Choose model with orifice size carefully due to the fact that these flow sensitive unloaders will not work properly with flow rates outside of their flow range. Available orifice sizes: ZK71 3.0 – 4.2 GPM, ZK72 4.2 – 6.6 GPM, ZK73 6.6 – 10.8 GPM.