Steam pressure gauge question

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c.p.huntington
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Steam pressure gauge question

Post by c.p.huntington »

I have a pressure gauge designed for air compressors on my engine (I've run my engine on
air many times but have not yet steamed it up). Can I use this same gauge with steam or will
I have to purchase a pressure gauge that will withstand the heat and moisture from the steam?
Thanks for any help that you can give me.

C. P. Huntington
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Fender
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Re: Steam pressure gauge question

Post by Fender »

The gauge will work OK, but you need to be sure to have a loop, aka "syphon", in the tubing going to the gauge, to keep the hot steam from entering the gauge directly. The syphon will fill with condensed water, so steam does does not enter the gauge directly from the boiler.
Dan Watson
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littleevan99
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Re: Steam pressure gauge question

Post by littleevan99 »

Here is the siphon for my gauge as an example.
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Bill_Gardei
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Re: Steam pressure gauge question

Post by Bill_Gardei »

Most "Bourdon Tube" gauges won't care if steam gets into them. But it never hurts to add the trap as described.
Marty_Knox
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Re: Steam pressure gauge question

Post by Marty_Knox »

Bill_Gardei wrote:Most "Bourdon Tube" gauges won't care if steam gets into them. But it never hurts to add the trap as described.
I beg to differ - apparently you've never seen a gauge blow up!
You should always have a condensation loop/siphon on a steam gauge line.
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DianneB
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Re: Steam pressure gauge question

Post by DianneB »

Marty_Knox wrote:
Bill_Gardei wrote:Most "Bourdon Tube" gauges won't care if steam gets into them. But it never hurts to add the trap as described.
I beg to differ - apparently you've never seen a gauge blow up!
You should always have a condensation loop/siphon on a steam gauge line.
Agreed! Not to mention that the Bourdon tube is designed to be accurate at room temperature and when they heat up, the accuracy goes south. They are also (usually) soldered with soft solder and it looses about 1/2 it strength at 350F. At around 400F it becomes a paste rather than a solid.
radial1951
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Re: Steam pressure gauge question

Post by radial1951 »

DianneB wrote:
Marty_Knox wrote:
Bill_Gardei wrote:Most "Bourdon Tube" gauges won't care if steam gets into them. But it never hurts to add the trap as described.
I beg to differ - apparently you've never seen a gauge blow up!
You should always have a condensation loop/siphon on a steam gauge line.
Agreed! Not to mention that the Bourdon tube is designed to be accurate at room temperature and when they heat up, the accuracy goes south. They are also (usually) soldered with soft solder and it looses about 1/2 it strength at 350F. At around 400F it becomes a paste rather than a solid.
*
Totally agree. Not to labour the point, but, the Boiler Code says that "A Water Filled Siphon SHALL be fitted between the gauge and the steam supply." Not required for an air reservoir.

Very interesting point about the operating temperature affecting the accuracy of the gauge, I wonder what the effect is and has it been tested. Luckily, the strength of the bourdon tube will be reduced at elevated temperatures, so in theory it will overstate the pressure (phew).

The Boiler Code also says pressure gauges SHALL have a range of at least 20%, preferably 50%, above the max operating pressure of the boiler, and that every pressure gauge SHALL be tested against a master of known accuracy, and the certified operating pressure indelibly marked in red on the dial face of the gauge. You cannot assume the nice new pressure gauge you just bought from your Live Steam supplier is accurate, no matter in which country it was made. (Or especially!)

We have the benefit of 2 centuries of other people's disasters...

Regards, RossG
radial1951
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Bill_Gardei
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Re: Steam pressure gauge question

Post by Bill_Gardei »

I actually knew what the replies would be before posting mine. I just wanted to see more explanation as to WHY there might be a problem. Something that was somewhat lacking from the initial set of replies. I might also point out that the large amount of tubing used in the example photo helps to temperature isolate the gauge as it was mentioned that gauge accuracy is temperature dependant. Copper is conductive (both for heat and electrons) so more tubing means better isolation from those hot manifolds.

Thanks to all -- Bill
apm
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Re: Steam pressure gauge question

Post by apm »

I am digging up an old thread here. I was wondering has anybody ever seen commercial pressure gauges fail under steam?

I make steam gauges that use commercial gauges as the base and my current base model gauge utilized high temperature solder with melting points in excess of 450°F seems to have dried up . I started trying to source alternative gauges but all of them seem to come apart around 350°F. Looking at the steam tables that would correspond to about 120psig which is right around where we run our locomotives. Doesn't seem to give a lot of margin.

However if you count on having the siphon at the bottom it would seem like that would protect the gauge from actually seeing the higher temperatures.

So I guess the question is what's people's experience using commercial gauges? Has anyone ever had one come apart under steam? Is a 350° melting point okay to use? I felt a lot better with the old ones that had a higher margin of temperature.
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Bill Shields
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Re: Steam pressure gauge question

Post by Bill Shields »

For our applications, as long as there is a a siphon, failures from overtemp are virtually unheard of using off the shelf commercial gauges.
Too many things going on to bother listing them.
Asteamhead
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Re: Steam pressure gauge question

Post by Asteamhead »

To all,
100 % agree to comments!
Bill, yes, there were issues now and then. I baught a medium size boiler which had an idnustry type 40 mm gauge with a range up to 10 bars. The boiler showed a steady 8 bars (120 psi) maximum preasure when fired up :twisted: After some (water) tests with a second one I found the boiler gauge was blocked mechanicaly at 8 bars even at twice that preasure :!: The inside brass gear seemed to block at that position.
Firemen's friend but definitely not mine!
And another hint: Make sure, tube and fittings towards the gauge are absolutely tight. Not one drip of water or even steam must be detected when under preasure :!: Just my two cents.

Asteamhead
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Bill Shields
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Re: Steam pressure gauge question

Post by Bill Shields »

Asteamhead:

Was the problem you are reporting related to high temp or just a defective gauge?..or maybe one that had been subjected to being over pressured?

In the USA, most clubs require that the user's gauge be compared to a standard gauge up to the safety relief pressure...so a gauge that is indicating incorrectly will be identified before it is allowed to be used.

Having worked in industry on full size boilers and other pressurized vessels for decades -> we never trusted a new gauge until it has been tested.
Too many things going on to bother listing them.
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