Which pressure gauge to use?

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Glenn Brooks
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Which pressure gauge to use?

Post by Glenn Brooks » Sun Nov 24, 2019 1:48 pm

Hello All,

Looking to buy a pressure gauge to monitor vacuum in my smoke box (12” coal fired boiler).

I see two types of gauges on Amazon: 0-10 and -10 to +10, with zero inbetween the high and low numbers.

I assume 0-10 would be fine??

Thanks
Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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Fender
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Re: Which pressure gauge to use?

Post by Fender » Sun Nov 24, 2019 3:35 pm

I don't think that either gauge will give you the results you desire, because you are needing to measure vacuum in fractions of 1 psi. A manometer that shows the smokebox vacuum as the difference in the levels of water in two columns would be more discriminating. There are also inexpensive digital manometers available.
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ChuckHackett-844
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Re: Which pressure gauge to use?

Post by ChuckHackett-844 » Sun Nov 24, 2019 4:14 pm

For permanent, you want "inches of water" gauge (maybe 0 to 3"). But this is also easily done with just a "U" of clear tubing with water in it for testing purposes.
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Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
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ccvstmr
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Re: Which pressure gauge to use?

Post by ccvstmr » Sun Nov 24, 2019 5:19 pm

Glenn... "U" tube or "slack tube" is the best low tech approach if you're just looking to get an relative vacuum reading. You can ty-rap the vertical legs of tubing. Don't crimp the "U" at the bottom. To get your reading...measure the height difference between two water columns. Can add some dye if want make reading easier. For reference purposes...27 inches of water column (nominal) is equivalent to 1 psi. If you think you're going to have so much vacuum (or pressure if measuring other things)...better get a piece of tubing at least 120" long.

If you're looking for something more accurate, you can purchase round gauge manometers. Probably find some on Ebay. I'm familiar with the Dwyer brand of gauges. You can even find gauges with a neg to 0 to pos range...or just get a 0 to pos...and switch the tubing ends to change to vacuum.

Hope this helps...but have to ask, why the concern about smokebox vacuum? Are you checking for smokebox tightness? ...trying to locate the best position for a blast nozzle? ...other? Carl B.
Life is like a sewer...what you get out of it depends on what you put into it!
I don't walk on water...I just learned where some of the stepping stones are!
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Bill Shields
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Re: Which pressure gauge to use?

Post by Bill Shields » Sun Nov 24, 2019 5:31 pm

U tubes are great but a little tough to take along with you around the track.

I have been using a Magnehelic for 20+ years. (Dwyer makes them now)

The one I have is good for 6" of water...which I don't see as being available any longer.

You can also 'offset' the needle so it settles in the center so you can go + / - 3" of water if for some reason you think you might be getting pressure in the smokebox.

It has allowed me to tune in both the blast nozzle and draught blower quite effectively.

yes, it is a little large to 'stick in the cab' but for testing / setup purposes a good way to go...

I have no experience with the digital critters now available, but anything that can give you 6" to 10" WC will work well for your purposes...and surprisingly, some of the digital units are less expensive...
Too many things going on to bother listing them.

Glenn Brooks
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Re: Which pressure gauge to use?

Post by Glenn Brooks » Sun Nov 24, 2019 9:35 pm

Thanks all. I made up a plastic U tube such as you all have recommended, to check my smoke box vacuum. Hope to see what it shows tomorrow. This will be the ”before” measurement.

Carl, main reason to do this, is I need to replace my existing blast pipes with a Lempor ejector system and want to find optimum vacuum settings as I experiment with nozzle sizes and maybe add a stack extension. My Ottaway is not now steaming well enuf to replenish what it uses. So hoping the manometer trick will make things easier to test.

Also, I am curious about how vacuum, aka draft, changes with different operating conditions - e.g. short trips, light loading around the track, etc, and how to compensate for poor draft that may be inherent in small backyard railroads. So thinking about a gauge to mount permanently to be easier to monitor and gather data.

Also my old antique Campbell Locomotive will need a new front end soon, so maybe interesting to compare with the Ottaway results, once I get to that point.

I’ll post any results I get tomorrow.

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

rkcarguy
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Re: Which pressure gauge to use?

Post by rkcarguy » Tue Nov 26, 2019 7:14 pm


Glenn Brooks
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Re: Which pressure gauge to use?

Post by Glenn Brooks » Tue Nov 26, 2019 8:47 pm

Ryan, I am rarely at a loss for words, but here, I think I am definitely on pause! :shock: :shock: :shock:

Plus, After getting NO vacuum reading out of my smokebox today with my home made manometer I may just go right out and buy one of these!

BTW, just reading Koopmans’s great historical accounting of steam engine development. The third or fourth steam locomotive ever built, in 1824 or thereabouts actually had two bellows affixed to the frame- each operated by the cylinders. Didn’t work out, but Lowes apparently is still hopeful!

Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

rkcarguy
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Re: Which pressure gauge to use?

Post by rkcarguy » Tue Nov 26, 2019 11:02 pm

I just felt some humor was called for :lol:

Hopefully you get it figured out, I would have thought the simple water column gage would have showed something.

Glenn Brooks
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Re: Which pressure gauge to use?

Post by Glenn Brooks » Wed Nov 27, 2019 2:34 am

Actually, I very much enjoyed your post -particularity opening the post and seeing the bellows - perfect humor, considering I was just reading about using one.

On to the serious stuff... front end researchers in the 20’s and 30’s were able to improve boiler performance routinely up to 42% by replacing the old single blast nozzle with multi orifaces and new stack geometry. They found in some cases the exhaust jet was so poorly configured it vented out the stack with out creating any significant vacuum - leaving the exhaust gasses to swirl around inside the smoke box, and a poorly burning fire. I think that’s what my front end (and grates) are doing.

Either I mounted the vacuum tube incorrectly, or there’s just nothing to measure. Iam going to redo the test tomorrow, lowering the pick up tube down towards the bottom of the front end shell. Maybe also alter the level of water in the tube. See what happens. All in all actually fascinating stuff - redoing the experiments that people tried 100 years ago.

Except these days we know what’s supposed to work- the old timers had no idea what would work, in many respects.
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

Pontiacguy1
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Re: Which pressure gauge to use?

Post by Pontiacguy1 » Wed Nov 27, 2019 8:22 am

Put your vacuum tube on the side of the smoke box, and then take your shop vac and stick it in the stack and see if your tube levels change. That will verify that your manometer tube is working.

Glenn Brooks
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Location: Woodinville, Washington

Re: Which pressure gauge to use?

Post by Glenn Brooks » Wed Nov 27, 2019 4:49 pm

Great idea 💡 I’ll try the vac!

glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

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