This Pressure Sensitive CAT Pump 7590 Regulating Unloader is designed for single or multiple pump, weep or multi-nozzle systems. This unloader maintains set system pressure and goes into by-pass with the release of the trigger or an obstruction downstream. Pressure is held in the line during by-pass with full pressure when the gun is opened or the obstruction cleared and minimal pressure fluctuation with the alternating use of multiple guns. 5-10% by-pass is necessary for optimum performance. Minimum 10 GPM per gun.