THE TEST RESULTS ARE IN

[Trainman4602]

I was finally able to test the safety valves mounted to a tee using one outlet in the boiler.

The question in my mind was. Will both pop off while mounted in the same outlet using a tee setup.

Well here are the results.

http://www.youtube.com/watch?v=YuNSU5wyVtE

[amadlinger]

Good to know!

[boomerralph]

Thanks, Dave for taking the time to research this question.

Ralph

[FredR]

Well, without watching the video, I would think that if the safeties are set at different pressures, they would NOT go off at the same time.

Now, to go watch how Dave's video to see the answer

[FredR]

Great demo Dave. I am just wondering though, when the first safety goes off, can the drop in pressure in the pipe affect the other safety? I guess I am using a water line as comparison. If you have two faucets on a say 1/2" water line, you open one and have great pressure, but if you open the 2nd, the water pressure drop at the first faucet opened. I know I am probably missing a pertinate piece info in the equation.
Fred

[BillF]

Great demo Dave. I am just wondering though, when the first safety goes off, can the drop in pressure in the pipe affect the other safety? I guess I am using a water line as comparison. If you have two faucets on a say 1/2" water line, you open one and have great pressure, but if you open the 2nd, the water pressure drop at the first faucet opened. I know I am probably missing a pertinate piece info in the equation.
Fred

I think the key points are that the viscosity of water is larger than that of steam, so there is more drag on the water flow, and mostly that the length of pipe is much greater in the water supply case. A longer pipe run, upstream of where the two lines to the faucets split off, means a large pressure drop.

- Bill Frensley

[ccvstmr]

...I would think as long as the cross-sectional area of the pipe tap off the top of the steam dome is sufficiently larger than the total relief area of the (2) safety valves, there wouldn't be any problem. As long as the piping arrangement with the (2) properly sized safety valves lifted does NOT allow the boiler pressure to continue to climb...it would appear that piping concept provides a workable "system".

Safely conducted experimentation is always a good way to prove (or disprove) a theory or concept. Thanks for sharing. Carl B.

[srrl5]

Dave,

In the video You said one safety is 120 the other is 125, yet with both safeties lifted you had 130 in the boiler, that means the two safeties don't have enough volume for the steaming capacity of your boiler. Which can be why the second safety is able to lift with the first one open.

David Rohrer

[Harold_V]

Dave,

In the video You said one safety is 120 the other is 125, yet with both safeties lifted you had 130 in the boiler, that means the two safeties don't have enough volume for the steaming capacity of your boiler. Which can be why the second safety is able to lift with the first one open.

David Rohrer

I considered that as well, but I'm of the opinion that the problem isn't the safeties, but the limit created by the use of the 1/8" supply. A test with the 1/4", were it possible, would either dispel or reinforce that notion.

The test behaved exactly as I expected it would.

http://www.chaski.org/homemachinist/vie ... =8&t=95846
(2nd post in the thread)


Harold

[Trainman4602]

I do agree with that. When I have the two safety valves in saparate outlets it easily handles the boiler output. The fact that they are trying to relieve the boiler thru one common outlet of the same size is why the boiler was able to bulid pressure even thou both safeties popped.

I wish I could have tested them using a 1/4 inch pipe.

[Harold_V]

The critical point here is that by adding a T and a second safety, one may not achieve the protection desired. Said another way, if the supply is just 1/8" pipe, it most likely is not a good idea to Tee to provide a second safety. I expect that would not be the case with a 1/4" or larger supply (for 1½" scale boilers).

Harold

[Trainman4602]

That is correct.

The conclusion is that mounting two safeties in the same outlet in the boiler will work providing that the outlet and all the piping is larger than the size of the outlet hole in the safety valves.

This is exactly why during the test the secondary valve (125lbs) popped because the pop off pressure was reached. The boiler continued to build pressure because the piping could not handle the volume of steam being generated.

It worked as intended when I mounted the safety in the proper outlet.

The experiment proved my theory that mounting two safeties on a tee when the piping is all the same size will not reduce the pressure as intended for the secondary valve to do. The pressure will continue to build.

The tee arrangement only provides a secondary fail safe incase the first(lower pressure) valve fails.