NIBCO Check Valve Automatic Stop F869B - Manual (Page 9)

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9
VALVE SALES INFORMATION
Technical Bulletin
July 1, 1980
September 26, 1969
Reissued May 20, 1985
(Everything You Always Wanted to Know About)
NIBCO F-869-B Automatic Stop-Check Valves
Stop-check valves are as essential to the safe operation of a multi-boiler plant as any other
safety device that is attached to a boiler, and have four very important functions in the steam
piping systems.
1. To act as an automatic non-return valve by preventing the back flow of steam from the
header to the boiler in the event of failure in the boiler.
2. To assist in cutting a boiler out of the steam system when it has ceased to fire. In this case
the disc automatically closes and prevents the pressure in the header from entering the
boiler.
3. To assist in bringing a boiler into service after a shutdown. This operation requires
considerable care when performed manually, but is accomplished automatically by a stop-
check valve without pressure fluctuations or disturbance of the water level.
4. To act as a “safety first” valve by preventing back flow of the steam from the header into a
boiler that has been shut down for inspection should the valve be opened accidentally.
There are three basic questions regarding the NIBCO stop-check valve:
1. What is a stop-check valve?
2. Where is it used?
3. How does it work?
Question #1 – What is a stop-check valve?
The purpose of a stop-check valve is predominantly in the steam line at the boiler steam
riser. It allows steam to pass through it from the boiler to the main steam header, but in
case the boiler steam delivery is interrupted, the stop-check will automatically prevent
steam from flowing back into the boiler. The stop-check valve is a back flow preventer.
Its function is the same as the swing or lift check valve in that it allows flow in one
direction but not in the opposite direction.
A stop-check valve can also function as a stop and throttling valve the same way as a
globe pattern valve is used.
Question #2 – Where is a stop-check valve used?
The stop-check valve is designed to be used between the boiler steam exit and the
steam header in a multiple boiler plant to serve as a backflow preventer and stop valve.