27.01 When is ant-siphon protection needed and how is it done?

Anti-siphon valves are used at aboveground tanks where fluid levels would be above the point of use with the potential for inadvertent siphoning of fuel out of the tank. The valve is installed in the fuel supply piping from the tank at the top of tank elevation.

Anti-siphon valves are also required for submersible pumps in aboveground tanks, since fuel can flow through the pump under siphon conditions.

There are 2 common valves used for anti-siphon protection: (a) spring loaded valves, or (b) normally closed electric solenoid valves or actuated valves. The electric actuated valves are sometimes preferred where there is a concern over the capability of a suction pump in reliably overcoming the spring force resistance of a spring loaded valve.

The spring loaded valve is a spring loaded angle check valve with a spring force sized to resist the static fuel head. They are selected as 1, 3, 5, 7 meters of head resistance and are typically adjustable within that range. The fuel transfer pump must overcome the spring force to allow the pump to open and flow.

Electric actuated valves are normally closed valves that open and allow flow when energized. Solenoid valves for submersible pumps are sometimes energized with the same electrical circuit as the pump to simplify control.