I am trying to determine the best valve configuration to control boiler feedwater. Should I use a normally open or closed valve? This is for an industrial water tube boiler that is not continuously manned. It has a 3 element feedwater system. We are currently replacing the valves and need to determine the pros and cons of each. I have received conflicting information from the boiler manufacturer, valve manufacturer, boiler control vendor.

 

Dear Friend,

In case of Boiler you should always use fail safe open valve for feed water application. This is just to ensure that in case of air failure or instrument supply failure, the valve opens fully and there will be no starvation in the drum water pipes, which may cause serous damage to drum internal. I think this is common practice of all the boiler vendors and every vendor provides the same reason.

 

Hey, you have to leave it open, or else it's no good! I've done it many times until I read it on eBay... try it, it will work!

 

Having a feedwater valve fail open is not always the chosen failure mode. Often a valve may fail closed on loss or air or loss of signal depending on the steam user. If high pressure boiler is supplying a steam turbine (or other critical steam user), then the choice may be to fail the valve closed. Worst case is probably that you replace some boiler tubes. If the valve fails open, the worst case is that you do a major turbine overhaul after the drum overflows into the steam line and water hammers the high pressure turbine blades.

-Arnold Dillon