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Yarway Blow-off Valve Blow-off Valve

Blow-off Valve
Blow-off Valve

Basic requirements for the design and use of blow-off valves are established by the ASME Power Boiler Code, Section l. The general form of a valve, the materials of its construction, allowable boiler pressures, and the installation of the valve are all determined by the code. Yarway blow-off valves are designed in conformance with all code requirements (ASME Section l, ANSI B31.1, ANSI B16.34).

Because the primary purpose of a blowoff valve is removal of dirt, sediment and scale, the boiler code requires that valves which have dams or pockets in which sediment can accumulate cannot be used in blow-off service. This means that ordinary globe valves cannot be used as blow-off valves.

Yarway valves are especially designed for the punishment of blow-off service in boiler systems with pressures of 3,193 psi.

The rugged construction of these valves can successfully withstand the combination of problems inherent in the service – a service in which high pressures result in high velocities which can cause wire drawing and cavitation of metal surfaces.

The valves must also withstand the corrosive environment created by acid cleaning of boilers, and the potential wear problems caused by precipitated solids.

The valves are also helpful in maintaining boiler level surge within desirable limits during quick startup of high pressure systems. Two broad categories of Yarway blow-off valves are available; those that operate on a sliding principle and those that operate on a seat-and-disc principle.

Seatless Valves 
No seat
    • Will not score with dirt
    • Will not plug with dirt
    • Will not leak 
“Live-loaded” packing
    • Will not leak after packing water 
Slow opening
    • Will not rapidly drain boiler drum

Unit Tandem Valves- A combination of hardseat-hardseat or hardseat-seatless valves in a single body 
• Eliminates pipe joints 
• Reduces potential leaks 
• Fits into a confined space

Hardseat Valves- Stellite valve and seat 
• Resists wear 
• Provides long service life

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