[HayZee518]

there is a clutch linkage between the pressure pump and the gas engine. with the gas engine running, the unloader is actuated and the clutch disengaged. when you press the nozzle handle, the pressure system senses the drop in pressure and closes the unloader and actuates the clutch that tells the engine to speed up. the water in is "just always there" when the pump is operating it takes the input water sucking it in and presurizes it for use. if you have an input water tank, chances there is a ball type float that opens/closes as the tank water is used up. a bypass from the pump may have a return line to the tank.