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Beach
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Join Date: Aug 2008
Posts: 3

Dp to GPM conversion formula

08/02/2008 1:59 PM

What is the math formula for converting differential pressure to gallons per minute.
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Anonymous Poster
#1

Re: Dp to GPM conversion formula

08/02/2008 2:15 PM

There isn't one
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Mikerho
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#2

Re: Dp to GPM conversion formula

08/02/2008 2:49 PM

Beach,

These two units are not compatible. A description of what you are trying to accomplish and what your setup is would be most helpful.

Mike

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Hendrik
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#3

Re: Dp to GPM conversion formula

08/02/2008 3:10 PM

Is this an orifice, nozzle, venturi or pump and is it water, air or other?

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Kilowatt0
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#4

Re: Dp to GPM conversion formula

08/02/2008 3:21 PM

What you are asking needs a LOT more information. You can calculate GPM based upon DP, but there are a lot of factors involved.

The size and schedule of pipe, size and type of orifice, type of fluid, type of taps (pipe tap, vena contracta ...).

I would suggest getting a book on the subject. A favorite of mine is: "Principals and practice of flowmeter engineering" (Foxboro - L.K. Spink 9th edition). It is an old book, but has all the formulas and information you need.

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Beach
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#5

Re: Dp to GPM conversion formula

08/02/2008 3:53 PM

Thank you everyone for your replies. This is a wafer type orifice on a chilled water loop. The pipes are schedule 40 and 18 inches in diameter.
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Mikerho
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#6
In reply to #5

Re: Dp to GPM conversion formula

08/02/2008 6:07 PM

Sooo... young Jedi! About orifice meter wanting to know you are. Graphic of meter here is being shown. Setup and variable designations have we here:

From the orifice plate, a tap upstream and a tap downstream there are. A differential pressure (DP) gauge from these two taps are fed. Proportional to the flow rate in the pipe, the difference in pressure in the upstream and downstream taps is. From the orifice plate, the distance of each of these taps comes into play does. To determine this, the Bernoulli Equation be used can.

Another way before you lies!

Measured at different flow rates both the DP and the flow rate need to be for the flow rate to accurately determined be. Calibration this is called. Yield a set of values relating the measured DP values to what the flow rate actually (measured) is, this will. Take this set of data and fit it to a curve you can. If evenly-spaced your data is, get a fairly accurate EQUATION (such as FLOWRATE = aDP2+bDP-c - an example ONLY this is, more or less linear the actual data may prove!) you can by using the curve-fit feature in Microsoft Excel.

Be advised; the volumetric flow rate temperature-dependent is. If operating conditions at a fairly constant temperature are, fine. If not they are, a way of compensating for temperature differences you must. Do this you can by doing a number of [DP vs flow rate] calibrations at different temperatures. End up with a 3D graph then you will - DP, flow rate, and temperature the axes will be.

If hard to read this post is, sorry I am.

Yoda

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Beach
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#7
In reply to #6

Re: Dp to GPM conversion formula

08/02/2008 8:04 PM

Thank you Master Yoda. That information is most useful.
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Mikerho
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#8
In reply to #7

Re: Dp to GPM conversion formula

08/03/2008 6:59 PM

Passed the first test you have, young Jedi. Gave me a GA you have. Proven yourself worthy have you!

Welcome you are. If more information on graphing in [2 independent and 1 dependent] variables you seek, contact me through private email you will.

Regards Best,

Yoda

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Anonymous Poster
#9

Re: Dp to GPM conversion formula

08/04/2008 2:56 AM

is there such a conversion? . ... Dp is pressure and gpm is flow. . .. .
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Ried
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#10
In reply to #9

Re: Dp to GPM conversion formula

08/04/2008 9:18 AM

There is not a direct conversion as you have noted.

HOWEVER, there is a relationship between the two that can be used with a calibrated orifice plate. The relationship is such that even without a calibrated orifice, very close estimates can be made based on the physical characteristics of the pipe, orifice, and fluid. Our "Yoda" Mikerho, has presented the information, and more exists in fluid mechanic texts and orifice web sites.

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