manometer accuracy

paulmars Posted By paulmars, Feb 12, 2018 at 11:21 PM

  1. paulmars

    paulmars
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    What is a good reasonable priced accurate manometer to measure my barometric damper?

    My furnace should be 0.025 and my flue should be -0.02. Looking at the gauges for sale i see accuracy (read
    inaccuracy) ratings that would make readings in the range that I need almost useless. Exp:

    0.3% of full scale 55.00wc (0.003x55=0.165) Does that mean that a reading of 0.02 could be off by as much as

    0.165?

    +/-0.3% of full scale 83.02 InH2O NKTECH NK-L3 (0.003x83.02=0.249)

    ±1.5% of full scale 4.00wc Dwyer 478A-0 (0.15x4=0.6)

    Am I doing something wrong here?


    tks,
    pa
     
  2. semipro

    semipro
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    If you're just looking for something to use once how about building one out of clear tubing, some water and food coloring. All that matters once its connected is the difference in height between the water level in each end of the tubing.
     
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  3. brenndatomu

    brenndatomu
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    Dwyer Mark II model 25...$25-30 on fleabay
     
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  4. paulmars

    paulmars
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  5. peakbagger

    peakbagger
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    I used to do large power plant size boiler testing on occasion and my go to manometer was clear vinyl tubing and food coloring. The trick is to mount the tube on a piece of plywood so its sloping at a shallow angle to accentuate the difference in the water levels. A draftsman's tee or dry wall tee makes good tool to mark reference lines on the plywood assuming it cut square. Nice thing about water manometer is there is no required calibration.
     
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  6. paulmars

    paulmars
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    i had considered making a unit, but for 25$ that dwyer is available. I dont understand how a home made would be more accurate.
     
  7. brenndatomu

    brenndatomu
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    I tried the homemade one...didn't work...bought a Dwyer 25 and done.
     
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  8. semipro

    semipro
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    I'm not sure how a tube filled with water doesn't work but at that price, I think I'd go with the Dwyer too.
     
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  9. paulmars

    paulmars
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    dwyer mark II 25 +/-3% of FS 3.0 is 0.09

    so, if it read your pressure at 0.03, that could really be anywhere from -0.06 to 0.12 and fall within the specified accuracy of 3% FS. Now i really doubt that it would swing negative for a positive pressure, so we could effectively limit that range to 0.00001 to 0.12 which is still an awful large range.

    pa
     
  10. brenndatomu

    brenndatomu
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    Yeah, I couldn't believe it either...but it didn't work...at all.
     
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  11. semipro

    semipro
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  12. brenndatomu

    brenndatomu
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  13. semipro

    semipro
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    A column of water is pretty sensitive. Did the Dwyer work well? I'm guessing the pressure difference must have been really low.
     
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  14. brenndatomu

    brenndatomu
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    Yes, still using it everyday...I have it permanently mounted for my wood furnace chimney...always check it after every load, just to make sure everything is dialed in...I've caught the barometric damper sticking more than once this way.
    Well, many/most wood furnaces call for -0.04 to -0.06" WC column draft....so, yeah, needs to be very sensitive...I've heard of some that spec -0.02" as the minimum! !!!
     
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  15. woodgeek

    woodgeek
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    I faffed around with water manometers for years, and home-made ones are useless below 0.2". The water makes a curved meniscus, and the meniscus has friction at the contact line on the walls of the tube (unless its chemically treated).

    I got a Dwyer off FleaBay and never looked back. Just gotta mount it steady and zero it.
     
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  16. Ashful

    Ashful
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    One word: Magnehelic, made by Dwyer. I wouldn’t even bother looking at anything else.

    I have a few, in different ranges. I even mounted one, 0.25” WC full scale, on the wall behind my stove.

    2b5e5cc35e13e5a9091cac207ecd2a24.jpg

    I’m headed out to my shop after lunch, to measure crankcase vacuum on a Kawasaki OHV v-twin, with my 5” WC magnehelic. Incredibly useful tools, IMO.

    Lunch is cheese and hard salami with Triscuits and some green olives, with a Weyerbacher Merry Monks to wash it down. Life is good.
     
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  17. paulmars

    paulmars
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    been looking at used
    2300-00 0.125-0-0.125" w.c.
    2300-0 0.25-0-0.25" w.c.
    2301 0.5-0-0.5" w.c.

    However, inst sheet says:
    "Diaphragm in vertical position. Consult factory for other position orientations."
    and: "Ranges below 17.5 in w.c. should be ordered using the –TA tilt angle option with the angle specified."

    ???

    p
     
  18. paulmars

    paulmars
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    and they still more pricey and Im generally scared of used.
     
  19. brenndatomu

    brenndatomu
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    Why's that?
    The Dwyer Mark II model 25 is a cheaper/simpler (more reliable?) device that is more than adequate for checking chimney draft
     
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  20. paulmars

    paulmars
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  21. paulmars

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    Have any in my wc range that you want to sell?

    pa
     
  22. brenndatomu

    brenndatomu
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    One just like that on fleabay pretty cheap right now...1 hour left, zero bids, $24.99 min. bid https://www.ebay.com/itm/Dwyer-Magnehelic-Pressure-Gauge-Model-2000-0-0-25in-includes-static-tip/173166970609?hash=item28518e46f1:g:OrMAAOSwWVhaifjS

    But I still think the model 25 is more than good enough for checking draft on a wood stove...heck, most people never even put a gauge on their chimneys...but if you can find a magnehelic for same/similar money, meh, whatever floats your boat...
     
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  23. Ashful

    Ashful
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    Family used to own an HVAC business, so I grew up seeing Magnehelics in the office. Standard tool in the industry. Every HVAC contactor carries them.

    Those water-based manometers I've seen a few here discuss are science project BS. They work, but it's awful hard to measure 0.05" WC with one.

    The Mark II 25 may work just fine, I'm not familiar with that one. But it looks like a homeowner-grade substitute for the Magnehelic, and they seem to go for $35, which is the same price as a used commercial-grade Magnehelic.

    Nope, but I picked up the two I have now on ebay. On is 0.25" WC for measuring chimney draft, the other is 5" WC for measuring crancase vacuum and other general purpose stuff. I think I paid $35 for each of them, and one came with a carrying case and stand.
     
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  24. paulmars

    paulmars
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    I need to measure -0.02 and +0.03wc.

    mount it inclined 10:1 for 10 times the resolution. https://www.amazon.com/Yellow-Jacket-78075-Water-&tag=hearthamazon-20
    Manometer/dp/B0038QHTK2/ref=sr_1_5?ie=UTF8&qid=1520466840&sr=8-5&keywords=manometer

    its graduated at 0.25 intervals and you can easily judge 1/5 of that. So, 0.25 included 10:1 the 0.25 would then be 0.025 and I could fairly accurately judge 1/5 of that or 0.005.

    thoughts?
     

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