inh2o@20c versus inh2o@4c

[USMCPMEL]

Does anyone know what units the Dwyer magnahelic gauges are calibrated in? I tried explaining this to the technical support people but they don't seem to have any idea what I am talking about.

[Squidley]

differential pressure in Inches of Water Column.

[USMCPMEL]

I am talking about the units. A lot of people are unaware but InH2O has a temperature designation associated with it. Due to the density of the liquid being different at different temperatures and the effect of gravity on that liquid. Therefore inH2O@4c is different than inH2O@20c. I am trying to determine at which temperature designation it is calibrated at. Not to be confused with the standard temperature of the lab. Does anyone here know what I am talking about?

[OlDave]

Yes, I know exactly what you are talking about but I don't have the time right now to get into it in depth.

Water @ 4°C is at its densest point so it takes more pressure to equal 1 inch of water.

The difference is less than 0.1% but it is measurable.

I will try to get back to you soon.

[USMCPMEL]

I understand the concept.I am just trying to determine what the factory calibrates it to. No one at the factory understands what I am talking about. I am trying to determine if they calibrate it in InH2O@4degrees c or InH2O@20 degrees c or InH20@60 degrees f. Someone said it is in 33K6-4-692-1 but I do not have access to GIDEP.

[dminesinger]

Per 33K6-4-692-1

The standard condition to which the Dwyer Hook Gage is corrected is that of standard pressure relative to a column height of water at 68 °F (20 °C) with a standard value of gravity of 980.665 cm/sec2

[OlDave]

Well I won’t argue (actually I would, but I’m not in a position to anymore) with the Air Force, but I will say they have been wrong more than once. But if everybody uses the same conversion then everyone’s measurements will agree, even if they are skewed slightly.

I really don’t think Dwyer knows that answer. And if they did at one time it was lost when the old fart finally retired.

You can download their current catalog https://www.dwyer-inst.com/catalog/
On page 524 there is a conversion table. (I am uploading that page) At the very bottom of the table they list the conversion from PSI to inches H2O as “PSI x 27.71 = in H2O”.

But if you look at the table, the ONLY point that applies to is 1.0 PSI.
Look down at the 10.0 PSI line on the chart and you can see that equals 276.8 in H2O. Even without pulling out my trusty old slide rule I can see that math is different.

I am uploading a pressure conversion chart from Sutron Corporation that throws even more confusion into the game.

They have reference tables for water at 4°C(39.2°F), 10°C(50°F), 60°F, 20°C(68°F) and 25°C(77°F).

Using Sutron’s numbers it looks like a Dwyer 1.0 PSI gage is referenced to 60°F and all the higher pressures are referenced to 4°C.

The conversion difference between 4°C and 68°F is only 0.18% so it really doesn’t make a significant difference for a 2% magnahelic.

So, my answer to your question is “I don’t know”, and I really doubt there is anyone left at Dwyer that knows either. Good luck with this one….

Well the Forum file size limitations won't allow me to attach the files but a good google search will find the Sutron conversion table for you.
Here is the link to their conversion chart:
https://www.sutron.com/wp-content/uploads/2013/12/PressureConversion.pdf

[USMCPMEL]

I am going to go with the 33K answer. SO I went with 20 degrees C.