Boiler Trim Blow-off Valves
Type B Seatless Blow-off Valve
- BALL BEARING YOKE for easy operation of handwheel.
- LONG STROKE LENGTH with threaded stem helps prevent water hammer resulting when valve is opened or closed too quickly.
- SHOULDER ON PLUNGER transmits force, in the closed position, through glands to packing rings.
- NITRALLOY PLUNGER tube resists erosion, high temperatures and sudden shocks. Seatless, sliding design provides "polishing" action
that lengthens life of packing rings.
- OPEN YOKE shows position of plunger in body.
- DUAL GUIDE LOGS provide proper alignment.
- COMPRESSION SPRINGS maintain continuous pressure on packing rings to keep valve tight regardless of plunger position.
Yarway Blow-Off Valves
Basic requirements for the design and use of blow-off valves are established by the ASME Power Boiler Code, Section 1. 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.(1)
Because the primary purpose of a blow-off 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 3,206 psig.
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 services.
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 seat-and-disc principle. They are summarized
in the next column of this page.
Flange and drilling data common to all Yarway Valve designs are shown below. All dimensions are consistent with ANSI standards and
supplied as listed unless otherwise specified.
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