Air over water boiler test?

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doublereefed
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Air over water boiler test?

Post by doublereefed »

I need to do a boiler test to check things before I travel. It's been a few years... thank you COVID.

Anything wrong with an air pressure over water test? My plan is to fill the boiler completely full right up to the safeties, which are the highest point on the boiler. Cap one and put a pressure fitting on the other. Use the loco pressure gauge and the compressor gauge to take it to 150, operating pressure is 100. Check the flue sheets and mud ring, etc. All of the hoses are rated for those pressures and significantly more, it doesn't seem like that should be an issue. Water against every other aspect of the boiler.

Am I missing something?

Thanks!
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Bill Shields
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Re: Air over water boiler test?

Post by Bill Shields »

not a good idea with an air compressor.

if something does let go..you have a lot of energy looking to be released.
Too many things going on to bother listing them.
ccvstmr
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Re: Air over water boiler test?

Post by ccvstmr »

Doublereefed...

Agree with Bill here...air over water is not a good way to check your boiler. Air can be compressed and yield erroneous readings. Water is not compressible.

However...you may have an alternate method on hand already. Do you have a tender hand pump? Remove the safety valves. Fill the boiler with water to the top. Plug the safety valve holes and keep on pumping until you get to your desired test pressure via your boiler pressure gauge. Can even replace one of those safety valve plugs with another pressure gauge...and monitor the two gauges as the pressure comes up.

Boiler tests vary by club. Sometimes the initial boiler test is done at 150% of MAWP (max. allowable working pressure). Subsequent annual tests can be done to 125% MAWP. Best to check with the track you're going to visit and see what their requirements are. Maybe contact their boiler inspector beforehand...so a test can be arranged and HE can witness/validate/certify your boiler. Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
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Dick_Morris
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Re: Air over water boiler test?

Post by Dick_Morris »

I was ready to make a test pump but found a "Hydraulic Pressure Test Pump" on Amazon for around $100. It's good to over 700psi. I already have enough projects to last a couple of lifetimes and I'd rather make parts rather than more tools. Since I would have to buy a hose and gauge and track down material the actual difference between a home build and purchase wasn't much. One caveat, the threads are not standard U.S. pipe threads and an adapter is needed.
Last edited by Dick_Morris on Mon Jul 19, 2021 10:01 pm, edited 1 time in total.
RET
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Re: Air over water boiler test?

Post by RET »

Hi Doublereefed,

I'm with ccvstmr and Bill Shields on this one. Even if you do things exactly the way you say, while there may be very little stored energy in the boiler side itself, there is a lot of stored energy in the air side of your setup and if anything carries away in the boiler, all that stored energy is available on the air side to make things happen in a hurry.

ccvstmr has a perfectly viable alternative which can be set up with relatively little effort. I used a very similar set up when I did the pressure test on our Big Boy.

Hope this helps a bit.

Richard Trounce.
doublereefed
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Re: Air over water boiler test?

Post by doublereefed »

Gents, thank you for the responses and the details. OK, I'm convinced air over water is not a great way to go. I do have a tender pump Carl, I just rebuilt it. Great plan, why didn't I think of that? And to be clear this is a home test to see if there are any issues before I drive the 8-12 hours to a club where a test is understandably required. Thanks again for the info and assistance.
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Bill Shields
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Re: Air over water boiler test?

Post by Bill Shields »

I always test at home

Assuming that you are new to this...a little bit of air in the system (top of the boiler) is not a bad thing...emphasis on A LITTLE BIT OF AIR.

When you have nothing but water. .a single stroke of the pump can cause the pressure to jump alarmingly in the middle of a stroke.

I have tested new small copper boilers by filling them with cold water and then either put them out in the sun or running warm water over them until the pressure came up to desired.... and it comes up fast it the boiler has no air in it.

With a little bit of air in the system the pressure climbs slowly.

Another trick that I like is a soft seat air compressor safety set to a pressure just above the test pressure tied into the pressure test system-> so that if you do something stupid all that happens is that you lift the safety...not damage the boiler.

Think ahead. Stuff happens when you get distracted -> and boiler repair are always the biggest headache imaginable.
Too many things going on to bother listing them.
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rudd
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Re: Air over water boiler test?

Post by rudd »

In 12" = 1'-0" scale, it's not unknown to fill the boiler with water then build a *small* fire to heat the water and expand it.
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NP317
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Re: Air over water boiler test?

Post by NP317 »

rudd wrote: Tue Jul 20, 2021 8:54 pm In 12" = 1'-0" scale, it's not unknown to fill the boiler with water then build a *small* fire to heat the water and expand it.
My full-sized steam days we did the same, but with a steam dome valve open to allow expanding water to escape until warm to the touch.
Then cap the boiler and hydro to pressure.
Early on I learned to hate that dreaded PING! of a stay bolt breaking, when the water was cold. Or any time. More repairs...
RussN
rkcarguy
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Re: Air over water boiler test?

Post by rkcarguy »

I'm admittedly not a live steam expert, but have several years of experience in an exchanger shop. We always pressure tested the exchangers in a tank of HOT water. Every once in awhile, we'd get a return with a complaint of coolant loss, and find it was tight when cold but leaked when hot.
To not have a huge explosion of hot water if a cap or block plate blew, a small expansion tank was connected to an air hose and then the air source from the compressor was closed. It also had the effect of a small leak showing up rather quickly on the pressure gage as dropping pressure, if for some reason one were blind and missed the bubbles in the tank. :)
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