Testing Accuracy of a 0.25 Water Manometer Using a 10:1 Inclined Mount

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Discussion Overview

The discussion revolves around testing the accuracy of a 0.25-inch water manometer, particularly in the context of measuring small pressure differentials in a flue application. Participants explore methods for creating known pressure differences to validate the gauge's performance, while also addressing issues related to the forum's functionality.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant seeks advice on how to deflect the gauge by known values of 0.1 or 0.05 inches of water for accuracy testing.
  • Another participant questions the type of manometer and requests a datasheet to understand its specifications better.
  • Several participants discuss the challenges of using the forum's quoting feature and suggest alternative methods to quote posts.
  • A suggestion is made to connect the manometer to a container with liquid to create a known pressure difference, though concerns about precision in adding or removing small amounts of water are raised.
  • One participant proposes using a U-tube manometer to measure pressure differences, emphasizing the need for a large bore to minimize surface tension effects.
  • Another participant introduces the idea of using venturis to measure small pressure changes, suggesting that a larger pressure difference could be achieved through design modifications.
  • Concerns are expressed about the accuracy of measuring very small pressure differences, with some participants suggesting that typical reading limitations may hinder precise measurements.
  • There is a discussion about the relevance of the gauge's accuracy for safety and proper combustion in the context of flue pressure measurements.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method to test the manometer's accuracy, and multiple competing views on the feasibility and precision of various approaches remain. There is also uncertainty regarding the gauge's performance and the implications of its accuracy in practical applications.

Contextual Notes

Participants highlight limitations related to the precision of measurements, the potential effects of surface tension, and the challenges of using second-hand equipment for calibration. The discussion also reflects varying levels of familiarity with the forum's features and the technical aspects of pressure measurement.

  • #31
sophiecentaur said:
The OP seems to hop seamlessly from manometers to editing posts but I think he probably has the right tools for posting now.

I just love that "Inclined Leg" job!
My first experiences with using manometers was with a Dwyer Mark II. Fond memories, except for what happens with the red oil if one attempts to store it upside down :). They are also a favorite with the coal burning crowd where they are used pretty much for the application I'm imagining the OP has in mind.
 
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  • #32
they charge 99$
"Don't know what Dwyer charges, but sending it back and having them check & correct calibration and provide a NIST calibration certificate"
 
  • #33
Dwyer Mark II (model 25 shown) accuracy is +/-0.09, so a reading of -0.02 could actually be anywhere between -0.11 to +0.07. I confirmed that with dwyer.
 
  • #34
"outlined, 3% of full scale is +/- 0.008" w.c. (0.008" in 0.25") so obtaining accurate measurements down to 0.02" w.c. is problematic in either case." The gauge I referenced is FS accuracy 2% which is 0.005. I am ok with +/-0.005.
 
  • #35
yes many flame heating (oil and otherwise) forum ppl suggested the dwyer mark II model 25 and I almost bought one. However, the accuracy makes it really useless. I even tried to get the manu to tell me if it is really effectively more accurate that then, just in the range that I need, after I zero it. they would not go there.

Another idea is the inclined tube manometer. 10:1
 
  • #36
paulmars said:
"outlined, 3% of full scale is +/- 0.008" w.c. (0.008" in 0.25") so obtaining accurate measurements down to 0.02" w.c. is problematic in either case." The gauge I referenced is FS accuracy 2% which is 0.005. I am ok with +/-0.005.

Could be I'm looking at this incorrectly, but not per Dwyer bulletin A-27, and specs at the web page for series 2000 gauges. The model xxxx-0 is 3%.
Accuracy:
±2% (-HA model ±1) of FS (±3% (-HA ±1.5%) on -0, -100PA, -125PA, -10MM and ±4% (-HA ±2%) on -00, -60PA, -6MM ranges), throughout range at 70°F (21.1°C).
 
  • #37
maybe u right. I am unhappy with dwyer email support on other issues. I asked what the accuracy was, since their page lists 2,3, and 4%. response was for that specific unit 2%. Still, I don't like used and new costs too much. Interesting is that dwyer also lists the same 3% for mark ii mdl 25 and for mark ii mdl 40-1 of 3% FS. So, 40-1 would be more accurate. I wonder why both have same stated FS accuracy.
upload_2018-3-7_9-13-26.png

3% of 1.0 is 0.03 and that is not accurate enough and no one is recommending this unit and I wonder why.
 

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  • #38
paulmars said:
However, the accuracy makes it really useless.
I cannot believe that a simple oil heater can require the sort of measurement accuracy that you suggest. If the concern is the rate of flow of exhaust gases then there will be many other factors involved than pressure. Tolerances can't be particularly tight. The flue layout spec for most boilers has some recommendations about length and bends which are pretty non demanding.
I suggest you visit a plumbing and heating forum and ask what they all do. Be prepared for a less friendly response when you actually suggest DIY for anything to do with heating. They will probably tell you to get it done 'professionally' and then go on to explain things in impossible non-Science terms. The words "idiot" and worse are to be expected if you suggest taking the bread out of their mouths but you may get the name of a suitable instrument from someone before the sky falls in.

You wrote "
" I wonder why both have same stated FS accuracy."
I think the answer could be that they just thought it up from nowhere.
 
  • #39
mount it inclined 10:1 for 10 times the resolution. https://www.amazon.com/dp/B0038QHTK2/?tag=pfamazon01-20

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?
 
  • #40
paulmars said:
mount it inclined 10:1 for 10 times the resolution. https://www.amazon.com/dp/B0038QHTK2/?tag=pfamazon01-20

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?
That will magnify the scale but its accuracy will depend on things like the bore being parallel with the sides and distortion through the glass sides at an angle. (And thickness of the glass)
I ask again where you got the information about the required accuracy. Or was it just the claimed accuracy of a recommended instrument? Those are two different things. I am sure you are worrying needlessly about this.
 
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