YQA 23 Generator Fuel System Valves

23.01 What are typical specs for fuel system manual control valves?

Fuel system valves should be carbon steel, stainless steel, or ductile iron. Brass valves common for water service have a low melting point which is generally undesireable for fuel service. Manual control valves are typically ball valves with stainless steel ball and stem and teflon seats. Butterfly valves are sometimes used, and these should have viton soft goods, since Buna or neoprene, common in water systems will degrade. While Buna is often listed in compatibility tables as acceptable for diesel fuel, in fact the additives common in diesel fuel will degrade the Buna. Ball valves should have locking handle at locations that may need to be secured for operational or safety reasons. An improved specification for fuel valves is that they be API rated for fire resistance. This is a carbon steel ball valve with a special seat design providing a stainless steel seat seal as a backup to a Teflon seal that could fail in a fire condition.onstruction. API rated valves are sometimes specified as the first valve in the piping where it enters a room, with downstream valves of standard carbon steel.

23.02 Where are anti-siphon valves used and how do they work?

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 0-5, 5-10, 10-15, 15-20 feet 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.

23.03 Where are emergency / fire safety valves and how do they work?

Emergency / fire safety valves are valves designed to close automatically in a fire condition. They typically have a design based on a normally closed valve that is maintained open by a fusible link which fails, causing the valve to close, at approximately 165 degrees F. Emergency valves are required as the first valve on a tank opening below liquid level. Most commercial tanks have top openings , so this requirement does not apply. Emergency valves are typically located: (a) at the discharge of a submersible pump on an aboveground tank, (b) where fuel piping from outside the building enters the building, and (c) where fuel piping inside a building enters a separate room such as a generator room or boiler room. Some versions or emergency valves are not UL listed or FM approved. A better quality emergency valve will be UL or FM approved. These approved valves are typically fire-rated carbon steel ball valves that are spring loaded to normally closed position, and are held in an open position by a fusible link. Jamesbury and Essex are manufacturers of FM approved emergency valves.

23.04 Where are backpressure regulating valves used and how do they work?

Standard regulating valves decrease an upstream pressure to a desired downstream pressure. A back pressure regulating valve maintain a desired upstream pressure. Most typically a back pressure valve is a diaphragm style valve, with Viton soft goods for diesel fuel compatibility. A back pressure valve is typically installed in a fuel circulation piping system serving boilers. The valve in installed at the transition in the loop between the fuel oil supply upstream – high pressure side of the valve) and fuel oil return (downstream – low pressure side of the valve. The boiler draws fuel from the high pressure side of the loop and discharges to the low pressure side of the loop.

23.05 Where are solenoid valves used and how do they work?

Solenoid valves are electric actuated valves that use an electric coil to raise the valve seat and allow flow. The valves are available as normally open or normally closed.costs Solenoid valves have the benefits of (a) fail safe close operation for normally closed valves, (b) fast acting, (c) relative low cost, and (d) simple wiring. Potential problems are : (a) failure with extended use, (b) fast close action can induce fluid hammer problems in piping, (c) dirty or deteriorated seat surfaces allow fluid leakage, (d) general lack of position feedback to controllers.

Solenoid valves are commonly used at the inlet of day tanks for flow control. A normally closed valve is used for normal day tank fill. A normally open valve is sometimes used in series to activate as high level stop valve. Solenoid valves are also used as (a) anti-siphon valves, (b) tank fill pipe overfill prevention valves. We do not recommend solenoid valves for tank selection, especially for filtration / polishing systems. The reason is that fuel leakage through dirty or deteriorated seating surfaces can cause tank overfills. We also do not recommend solenoid valves that operate in a normally energized state. A critical aspect of solenoid valve application is installation of a strainer (recommended 100 mesh) immediately upstream of the valves. Piping debris can damage seating surfaces or obstruct proper seating to allow leakage through the valve.

23.06 Where are actuated valves used and how do they work?

Actuated valves commonly used in fuel systems are quarter turn 2 way ball or butterfly valves, and sometimes 3 – way ball valves. Actuators for commercial fuel systems are typically electric, and not pneumatic. Actuated valves have the benefit of (a) tighter sealing than a solenoid valve, (b) position indication, (c) relatively slower action to avoid fluid hammer issues, (d) availability in larger sizes than solenoid valves, (e) available as fire-safe, flanged, or socket weld valves, (f) integral position indicators, (g) integral manual over-ride mechanisms. Drawbacks include: (a) more expensive than solenoid valves, (b) installation and wiring can be more complex, (c) require special features for fail safe close. Actuated valves are used for tank selection in multi-tank systems for supply, return, and fill piping. They are also used for day tank inlet valves and anti-siphon valves as alternatives to solenoid valves.