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Steam boiler safety valve

stevenkd5017

Registered
Would this work for a safety valve for a small boiler, about 12" in diameter by 18" high? It is rated for liquids up to 450 degrees but it does not specifically say steam. https://www.grainger.com/product/AQUATROL-Bronze-Adjustable-Relief-Valve-3ETU3. I have tested the boiler to 100 lbs but don't plan on running more than 40 to 50 psi and like the idea of the adjustable pressure as I have several different engines I would like to run with it.
Thank you.
 

stevenkd5017

Registered
I'm going to step out on a limb here and say no, it says for liquid use, like for sprinkler systems and water heaters. I think steam valves are ASME rated.
Thank you I am thinking the same thing it said it was rated to 450 degrees but it does not specifically say steam. I have sent a note to the company for clarification.
 

Odin

Subscriber
Last Subscription Date
07/13/2019
Boiler safety valves are indeed supposed to be ASME rated for the task. They also must be sized to suit the boiler such that the boiler cannot realistically produce steam faster than the safety valve is able to blow it down, that way no matter how wild the fireman gets it is impossible for the pressure to rise above the stamped MAWP.

You'll need to know how much heating surface your boiler has, as I recall the equations for sizing a safety valve are based on the heating surface. Heating surface is used to calculate how many lbs/hour of water can be evaporated into steam, and then a safety valve is selected that has a higher lbs/hour flow rate- but not too high or it becomes wasteful by blowing down too fast and causing problems. You want the valve sized to where it will stay open for a minute or two when it opens, but will always reduce the pressure and close again.
 

Ryan Williams

Subscriber
Last Subscription Date
01/20/2019
Would this work for a safety valve for a small boiler, about 12" in diameter by 18" high? It is rated for liquids up to 450 degrees but it does not specifically say steam. https://www.grainger.com/product/AQUATROL-Bronze-Adjustable-Relief-Valve-3ETU3. I have tested the boiler to 100 lbs but don't plan on running more than 40 to 50 psi and like the idea of the adjustable pressure as I have several different engines I would like to run with it.
Thank you.
I don't want to go crazy and write an essay so here's a hopefully short enough and simple answer.

No, that valve should NOT be used on a steam boiler. Someone here should be able to direct you to a good shop. You have two options depending on what you are doing. If you are not going to be running at public events (or if your State classifies your boiler as "unregulated hobby" size), you can use a safety valve from a 7.5" gauge model steam locomotive. It would be around the right size and be built for the correct purpose. Also relatively cheap. If you are running at a public event and the State does not classify you as "unregulated", you must us the appropriate ASME type valve. A proper safety should be an ASME certified type valve with a "V" stamp in or adjacent to the clover symbol on the tag. The "V" stamp is important because that indicates it is built for steam use on a fired boiler. These are more expensive but not hard to get from the right supplier.

Important to note, an ASME valve stamped "UV" is not the same as a "V" stamped valve. The "UV" indicates that the valve is intended for steam on a UNfired boiler. I have seen people use these by mistake and they work just fine, but they are not technically correct and would not pass a state inspection. I did ask an inspector one time and supposedly, the only practical difference is the tolerance spec for the popoff pressure, nothing different in the guts or such. Something like 5% tolerance on a "V" and 10% on a "UV". I don't know for certain, so I just stick to the book.

 

stevenkd5017

Registered
I don't want to go crazy and write an essay so here's a hopefully short enough and simple answer.

No, that valve should NOT be used on a steam boiler. Someone here should be able to direct you to a good shop. You have two options depending on what you are doing. If you are not going to be running at public events (or if your State classifies your boiler as "unregulated hobby" size), you can use a safety valve from a 7.5" gauge model steam locomotive. It would be around the right size and be built for the correct purpose. Also relatively cheap. If you are running at a public event and the State does not classify you as "unregulated", you must us the appropriate ASME type valve. A proper safety should be an ASME certified type valve with a "V" stamp in or adjacent to the clover symbol on the tag. The "V" stamp is important because that indicates it is built for steam use on a fired boiler. These are more expensive but not hard to get from the right supplier.

Important to note, an ASME valve stamped "UV" is not the same as a "V" stamped valve. The "UV" indicates that the valve is intended for steam on a UNfired boiler. I have seen people use these by mistake and they work just fine, but they are not technically correct and would not pass a state inspection. I did ask an inspector one time and supposedly, the only practical difference is the tolerance spec for the popoff pressure, nothing different in the guts or such. Something like 5% tolerance on a "V" and 10% on a "UV". I don't know for certain, so I just stick to the book.

Thank you for the information. I got a note back from aquatrol that said that said steam valves require a lift lever they are going to contact me on Monday. I like the idea of the locomotive valve also and will look into that. Thanks again.
 

GreasyIron

Subscriber
Last Subscription Date
12/28/2019
What about a valve like this one for 40 lbs and under ( 250 Degrees F )
ASME coded
the pressure can be adjusted on these
I'm surprised that Ryan's description and images hadn't firmly put the question to bed, but see some confusion still exists. I'll assume this thread is still about outfitting a fired steam boiler to ASME code, not merely a pump relief or a table top [just my terminology of the moment, but should paint the picture] toy like Jensen, Mamod, etc.

It must be stamped with the set pressure & output in lb/hr [not cfm], and sealed so it cannot be reset without visible tampering. It will also be stamped as shown above instead of UV or something else.
 

Ryan Williams

Subscriber
Last Subscription Date
01/20/2019
Depending on the type you need, here's a couple places you can contact to get the correct safety. They should be able to help you determine the correct size and type valve you need or direct you to someone who can. These links are focused around model locomotives but should be perfectly applicable to what you need without going way overboard on things that are not necessary for someone like you. Being from the modeling realm of things, they should also be much more affordable than a typical commercial type valve.

http://www.godshallscustommachining.com/home.html
http://superscale.biz/Superscale2/Index.html (Sorry, I not sure how this website works, but there's the name at least)
http://www.americanmodeleng.com/index.html
http://www.littleengines.com/
 

GreasyIron

Subscriber
Last Subscription Date
12/28/2019
Ahhh, I had to look at that original diameter again - more comparable to "Live steam/scale model" size rather than either table top or to the full sized boilers mostly discussed in this sub-forum. For all I know, NY or somewhere might still have regulations on it, but I cannot think of a state that does on at your size.

So, an adjustable may do. Interesting on the AmericanModelEng sight that Ryan linked, Kunkle must not make a section I valve small enough, so they're using a section III for ASME valve. That may even be on the high end of output here, but I'd sure think a call to one of them would steer you right. Except that ASME one, I'm sure the prices aren't much beyond McMaster Carr, etc - and it is still steam, so going with a tried and true is still most wise.

Oh, for varying pressures these might be cheap enough you could set one at each pressure, and switch the entire valve rather than reset. Double pressure will roughly double output too, but you may easily be at a range where one size still fits all for you. Again, an easy question, that one of the live steam people should be able to answer easily.
 

stevenkd5017

Registered
Thank you for all the replies and ideas. I am new to steam, the first thing I want to do is be safe, both myself and anyone around me. The unit did come with a safety valve and when I can get back to the engine trailer I am going to see if I can see any details on how it was made or what pressure it is set for. The gauge that was on the boiler only goes up to 30 psi so I think that the actual unit was used for something under that. What is the best way to test the safety valve once I get the unit back together. Is air pressure a good way, should I use the hydraulic tester again or is the only sure way to fire it up with steam? I am thinking air pressure up to 50 lbs would be ok as I hydraulic tested the boiler to 100 psi. Thank you.
 

GreasyIron

Subscriber
Last Subscription Date
12/28/2019
Thank you for all the replies and ideas. I am new to steam, the first thing I want to do is be safe, both myself and anyone around me. The unit did come with a safety valve and when I can get back to the engine trailer I am going to see if I can see any details on how it was made or what pressure it is set for. The gauge that was on the boiler only goes up to 30 psi so I think that the actual unit was used for something under that. What is the best way to test the safety valve once I get the unit back together. Is air pressure a good way, should I use the hydraulic tester again or is the only sure way to fire it up with steam? I am thinking air pressure up to 50 lbs would be ok as I hydraulic tested the boiler to 100 psi. Thank you.
You can test it first on air without being attached to the boiler. But the only way to know exactly how it will behave is firing the boiler. Firing slowly, you should be able to bring the pressure down easily, should anything not go as hoped.
A 30psi gage would only give you 15psi mid-range. What was the original use? That pressure isn't very high for a power boiler.
 

stevenkd5017

Registered
You can test it first on air without being attached to the boiler. But the only way to know exactly how it will behave is firing the boiler. Firing slowly, you should be able to bring the pressure down easily, should anything not go as hoped.
A 30psi gage would only give you 15psi mid-range. What was the original use? That pressure isn't very high for a power boiler.
It was originally used to run a fan in a tabacco shed on what I think was a homemade steam engine. I was planning to get a new gauge and would like to run the boiler around 40 to 50 psi sometimes. One of the reasons I bought this boiler and engine is I purchased several small model engines at an auction and wanted a steam source to run them. One of them is a Stuart Sirus genset that I would like to run on it and I think I will need the 40 to 50 psi to get it to generate power. I like the idea of testing the valve on air understanding that it may act differently on the boiler. And I do plan to us a propane burner so I could shut it down quickly. I am going to get it running this year, I have had it for over a year and keep getting distracted, but I want this and a couple of the engines ready for the show season in the fall. Thank you for the help.
 

James Bosma

Subscriber
Last Subscription Date
02/03/2016
Can you post a picture of your boiler ?
Is it home-made or a production ?
I use a electric steam iron boiler to run my model steam engines.
It runs around 25 to 40 lbs range at the moment. I would like 35 to 40 range better, lasts about 8 hrs on a fill
I'm lucky and have a " under 10 square feet heating surface " exemption for my models
I've attached the act if you like to read
 

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stevenkd5017

Registered
Can you post a picture of your boiler ?
Is it home-made or a production ?
I use a electric steam iron boiler to run my model steam engines.
It runs around 25 to 40 lbs range at the moment. I would like 35 to 40 range better, lasts about 8 hrs on a fill
I'm lucky and have a " under 10 square feet heating surface " exemption for my models
I've attached the act if you like to read
Here are a couple of pictures.
 

Attachments

Odin

Subscriber
Last Subscription Date
07/13/2019
That does look like it already has a safety valve on it. It also looks like its an old rivetted lap-seam construction. I would be wary of operating that without a very careful inspection. This forum has tons of information on how to evaluate a vintage boiler's condition and determine its safe working pressure. Rivetted joints by themselves are not a problem, many boilers built 100 years ago are still in good health and routinely operate above 100 PSI. But being a lap seam boiler means there is additional stress cracking and corrosion risks that need to be taken into consideration before sizing a safety valve to fit it.

I don't think I would want to operate this outside of private on the farm use unless your state inspectors went over it with you and gave you the okay. And even then, I'd find somebody local that has more experience with boilers to go over it with me and make sure I'm not forgetting anything.
 

stevenkd5017

Registered
That does look like it already has a safety valve on it. It also looks like its an old rivetted lap-seam construction. I would be wary of operating that without a very careful inspection. This forum has tons of information on how to evaluate a vintage boiler's condition and determine its safe working pressure. Rivetted joints by themselves are not a problem, many boilers built 100 years ago are still in good health and routinely operate above 100 PSI. But being a lap seam boiler means there is additional stress cracking and corrosion risks that need to be taken into consideration before sizing a safety valve to fit it.

I don't think I would want to operate this outside of private on the farm use unless your state inspectors went over it with you and gave you the okay. And even then, I'd find somebody local that has more experience with boilers to go over it with me and make sure I'm not forgetting anything.
Yes it does have a safety valve but as I understand it a steam safety valve should requires a lever on it. i am going to examine it more closely when I get back to the engine trailer it may say on it. If not I will test it with air first to see what pressure it is set for but I suspect it will be 15 or 20 psi as the gauge only goes to 30 psi. That would be sufficient for most of my needs but I have a Stuart Sirius genset that might need a little more say 40 to 50 psi as long as the boiler tests out ok. Right now everything is at the planning stage. Like you say the first thing is to insure the boiler is safe to run. I ran a hydraulic test to 100 psi in the fall but I still need to get the inspection plug out and give it a good inspection as well as rerun the hydraulic test a couple more times. I also belong to a club with some very experienced steam guys that I am going to have go over it with me before proceeding with actual firing. I would rather have it sit doing nothing than to have an accident where someone gets hurt.
 

Jim A

Registered
You also want to make sure that your gauge reads at least 20 percent higher than the setting of the safety valve. So if your valve is set for 50 PSI, the gauge should be able to read 60 PSI. You have to be able to read above 50 in case it doesn't open. Then you will know you have a problem and be able to shut it down.
 

Jim A

Registered
"Jim A, post: 1643485, member: 118383"]
Updated:
You also want to make sure that your main steam gauge reads at least 50 to 100 percent higher than the setting of the safety valve. So if your safety valve is set for 50 PSI, the gauge should be able to read at least 75 PSI. You have to be able to read above 50 in case it doesn't open. Then you will know you have a problem and be able to manually shut down the boiler.

I edited the above. I found in my book that the gauge should be 1 1/2 to 2 times Maximum Allowable Working Pressure (MAWP).
 
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