Flow Finder Tip #13

Every once in a while, we'll get an inquiry regarding the pressure drop across the calibrated orifice of our Flow Finders. In order to give you a better idea of how insignificant the pressure drop is, we'd like to show you some data from our testing process. At System Studies we use Water Column in Inches (or Inches W.C.), which is a common measurement of pressure, to illustrate the pressure drop of the devices. An Inch W.C. is the pressure necessary to cause water to rise one inch in a tube or manometer.

The maximum pressure drop across a System Studies Flow Finder of any range is 5.2 Inches W.C. This is an extremely minute pressure drop, the equivalent of 0.188 Pounds per Square Inch (PSI).

Following is a table showing some typical Flow Finder readings, with the pressure drop converted from Inches W.C. to Pounds per Square Inch. Note that the flow for each Flow Finder range is measured in Standard Cubic Feet per Hour (SCFH).

		0-9.5 SCFH	0-19 SCFH	0-47.5 SCFH	0-95 SCFH
Inches W.C.	PSI	Flow Finder	Flow Finder	Flow Finder	Flow Finder
0.0	0.0	0.0	0.0	0.0	0.0
1.0	0.036	4.2	8.3	20.8	41.7
2.0	0.072	5.9	11.8	29.5	58.9
3.0	0.108	7.2	14.4	36.1	72.2
4.0	0.145	8.3	16.7	41.7	83.3
5.2	0.188	9.5	19.0	47.5	95.0

From the table above we can see, for example, that a 0-9.5 SCFH Flow Finder, when reading 5.9 SCFH, is creating a pressure drop of only 0.072 PSI. This is only two Inches W.C.

The table also shows that when any of the Flow Finders are reading full scale, there is a 0.188 PSI drop across the calibrated opening. Therefore, the pressure drop across the Flow Finder will be anywhere in the range from 0.0 PSI to 0.188 PSI, or no more than 5.2 Inches W.C.

If you have any further questions regarding the pressure drop in Flow Finders, or Flow Finders in general, please give us a call.

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