RDEXP Black 10mm Rubber and Metal One Way Valve Fuel Line Hand Primer Bulb for Marine Boats Parts Frequently used as a hand pump in boats for fuel supply to the out-board engine. Hand bulb primer to suit petrol of comes with a one way valve installed to help quickly prime the fuel system. It made of high quality rubber and aluminum; Has the metal ends and works well Suitable for carburetor and low pressure fuel systems.