Accurate Differential Water Pressure Measurement

[whenry]

When measuring differential pressure across a set of heat exchanger tubes in the 3 to 6 psi differential pressure range, what are the best practices to obtain an accurate measurement?

Then when using the information to define and use a Cv value to measure flow what is the typical accuracy that one can expect?

Are there articles and or instrument suppliers guidelines available on this subject?

 

[ports394]

I'm still learning.. so my advice may not be what the more experienced engineers suggest.

I would have a cross on the inlet and outlet feed pipes.
Use 2 identical pressure gauges on the inlet and outlet. Make sure these gauges read identically, through prior testing, known values etc. As a backup, if dP is what's really important, i would use a dP pressure gauge connected to the 4th leg on each of those crosses.

You should be able to use some clear tubing, or if it's feasible swagelok tubing and setup your dP gauge across the HX.

This way, you have 2 measurements, that will give you the same result.

 

[unclesyd]

Look up Differential Cells as they will give you the information you need.

 

[unclesyd]

My previous post should have been look up Differential Pressure Cells.

 

[ports394]

unclesyd, do you mean something electronic like this?

http://www.us.endress.com/eh/sc/ame...ctProductURL=6F00264904F79C8BC1256EEF003642DC

Because I was thinking a simple analog, magnahelix style dp gauge would work. They make gauges for liquid dP measurements, and are very sensitive in the 0-5 psi range.

 

[ports394]

http://www.dwyer-inst.co.in/series-4000.htm

 

[unclesyd]

As you state you want something simple and portable. here is one of several differential meters from Extech. Depending on what accuracy you will need these type meters tart at around $175.00 and go up depending on the range and accuracy needed. There are a number of brands out there it's just that I've used the Extech.
If you want very simple measurements like the old days you could go to a u-tube manometer and have some fun when you blow mercury allover the area..

http://www.extech.com/instruments/product.asp?catid=15&prodid=

219

 

[ports394]

http://www.extech.com/instruments/resources/datasheets/HD700_HD750_HD755data.pdf

Where is the sensor?

 

[btrueblood]

Dunno, unclesyd, but on other websites the Extec units are listed for air or dry gases only.

This one is rated for use with water:

http://www.grainger.com/Grainger/DWYER-Digital-Hydronic-Manometer-2HMB1?Pid=search