measuring pressure drop

Old 09-29-06, 03:42 AM
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measuring pressure drop

Quick question. I'm considering replacing galvinized water piping in my old house- to start with the just main branch in my basement. It's a two family house with 3/4" copper to the basement, then old 3/4" galvinized for the rest of the system.

No surprise - there is considerable resistance in the system. I'd like to see how bad the system is now, and measure how much I change the resistance as I upgrade it.

Is it correct for me to 1) measure pressure at a point close to the meter, while running a known flow, and then 2) measure at a point close to the end of my system, with that same flow, then 3) subtract the pressures. Knowing the length and fittings between the two measurements and the flow, I can compare to a new pipe flow chart and see how much resistance I have compared to spec resistance for galv pipe and estimate what corrosion/deposits in the pipe are doing to me and how much repiping with PEX will improve things.

Does this sound right? Thanks.
Old 10-01-06, 07:36 AM
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pressure + flow

I think that you doing over-kill, if you have galv. it will have to be replaced. I would not check the flow at more than two points, one at the meter and one at the house, i.e. hose bib, this would be a static test with nothing running. That will give a pressure drop figure. The rest of your question will drive you out of your mind, what you propose is not something that a person in the trades would do. Bottom line, don't over think, lots of luck.

"If all else fails, read the directions"
Old 10-01-06, 08:44 AM
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I agree that what you propose will serve no usefull purpose because you don't know how much pressure drop there will be if not restricted.
What you can do is measure the pressure at a spot close to the meter with a tap flowing at the far end of the system.
When the piping is changed you can do the same test and if the line was plugged you should get a lower pressure reading because of increased flow.

To go further you could measure the pressures when different taps are open to check each line's before and after pressure drop.

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