# Steam Pressure Relief Valve



## Steve J (Oct 14, 2013)

where can I find prints for a pressure relief valve for my steam donkey engine. In the plans he calls for FTT-12 relief valves. not sure what those are and would buy them if I could find them but no good on a search. Just to clarify it is the william harris donkey engine and the plans are from live steam magazine. thanks steve


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## kvom (Oct 14, 2013)

Safety valves can be pretty simple:  the valve itself is a steel ball held in place by a spring.  The spring itself is retained by a threaded plug that allows the release pressure to be adjusted by compressing the spring.

The spring is sized according to the boiler pressure and the size of the ball.  Use stainless spring and ball.

The live steam community has suppliers for safety valves.  What's the working pressure of your boiler?


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## Steve J (Oct 14, 2013)

not sure of the working pressure. I was going to set the relief at 100 psi. the boiler is 1/4" schedule 40 pipe with 1/2" type k copper tubes. the plans dont specify any working pressure.


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## chrsbrbnk (Oct 15, 2013)

steam relief valves are made so that when it pops it would stay open until the pressure drops a given amount below the pop pressure a typical amount  would be 4%  it might be fairly difficult to display a home made safety valve most threshing shows don't allow them  but you could run it at home in most states    the size of the safety valve is closely related to boiler size and capacity   too large and your steam pressure would drop very quickly on its popping.  too small might be pretty hazardous,  how big is the boiler?


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## Charles Lamont (Oct 15, 2013)

Steve J said:


> not sure of the working pressure. I was going to set the relief at 100 psi. the boiler is 1/4" schedule 40 pipe with 1/2" type k copper tubes. the plans dont specify any working pressure.



You are saying you have published boiler drawings which do not specify test and working pressures?


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## kvom (Oct 15, 2013)

100 psi is right in the range of most  model locomotive pressures, so commercial safeties are widely available.   Locoparts.biz sells a some in the ~120 psi range.  You will need two of them, one with a higher release pressure than the other.  If the lower pressure safety sticks for some reason, the other will release later.


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## Steve J (Oct 15, 2013)

Charles, sorry for the delay. the drawings are published by live steam magazine and do not have any pressure or test specs. I am going to make a relief valve as this boiler will likely never be steamed or pressurized. Iam trying to make it true to the prints for the visual effect and will most likely put an inlet for compressed air. thanks for the help, my question is answered. steve


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## Neil K (Oct 16, 2013)

Steve:

Could you let me know which boiler plans you are referring to? I'd like to look up the information to see if we've missed something.

Thanks!

Neil
LSOR


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