Bypass 24V BP63-0517931 for pumps XPi12 to XPi63 The by-pass valve is a 24 Volts solenoid valve. When not activated, it enables pump output to link up to pump inlet When activated, the pump operates normally (output flow. A drain line has to be installed between the By-Pass valve and the hydraulic tank of the vehicule to ensure sufficient oil circulation and a good cooling into the pump. In any case, the connection to the tank must be done below the oil level.