Made in the U.S.A., Preferred invests in continued innovation on time-tested products like the Low Vacuum Anti-Siphon (Or Syphon) Valve. The Anti-Siphon valve was one the very first products ever brought to market by Preferred close after its founding in 1920. Preferred originally entered the oil and energy industry as a Fuel Oil component provider, and the original Anti-Siphon valve designed by founder, Gerald Bohn. Since then it has become a safety, code-required fixture in fuel oil designs.

Anti-Siphon Valves prevent oil spills caused by oil being siphoned from the storage tank onto the boiler room floor. The valve automatically shuts off the oil flow in the event of a broken or inadvertently left open oil suction line. This protection is required by many codes and is recommended on all installations where any level of oil storage tank is above the transfer fuel oil pump.

The original MODEL A valve is furnished for various hydrostatic heads: up to 5′, 5-10′, 10-15′, and 15-20′ (as measured vertically from the level of the oil in the fuel oil storage tank to the pump inlet).

The Low Vacuum version of the Anti-Siphon valve is available that will open with only 2” Hg of suction available, and it is designed for application between the day tank and the generator pump. Low Vacuum Anti-Siphon Valve is UL Listed. This Low Vacuum Anti Siphon Valve is available in ½” up to 2” NPT. Low vacuum version only comes in 4′ head size.

In the past, using anti-Siphon valves between the day tank and the generator was discouraged because of low vacuum capability of generator pumps. A generator fuel oil pump may only be able to pull 5 in. Hg – a filter installed between the day tank and the generator pump takes a 2-3” Hg pressure drop. So, only 2” Hg could be available to open an anti-siphon valve, posing a problem for most designs.

Leaving the anti-siphon valve out of the design between the generator and the day tank could present the possibility of the day tank contents being siphoned out of the tank, should there ever be a pipe break between the day tank and generator pump.

Engineers addressed the need to prevent siphoning from a day tank by installing a solenoid valve that opens when the generator pump turns on. BUT, this solenoid needs to be wired and is dependent on the controls functioning properly. This can cause additional complications.

With the Low Vacuum Anti-Siphon valve version, Preferred addressed the problem by providing a solution to fit a smaller application, most commonly, between a day tank and a generator and its pumps.