DIY Home Improvement, Remodeling & Repair Forum > Pipe Sizing & Flow Meters

03-27-2014, 05:22 PM
kok328
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Pipe Sizing & Flow Meters

I have a situation where I can't seem to find a straight answer.
I've tried some engineering websites with no luck.

What I'm trying to determine is how much pressure loss with I experience by reducing a 3" pipe down to 2" with a 10hp, 120/gpm submersible well pump.

I have a flow meter installed in the 3" pipe but, it's minimum flow range is 3gpm. I need to find a way to detect flow as low as .5gpm.

It is being proposed that I reduce the size of my pipe from 3" to 2" to accommodate a lower gpm meter but, I'm concerned about pressure loss, thus my original query regarding pressure drop.

I also did some limited research on an ultra-sonic flow meters but, can't seem to find one that is correct for a 3" CPVC, Sched 80 pipe with well water inside it.

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03-27-2014, 05:55 PM
JoeD
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That's a complicated question, because when no water is flowing there in pressure loss. It is equal. The more GPM you use the more potential there is pressure loss.

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03-27-2014, 08:00 PM
Wuzzat?
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Try
http://neutrium.net/fluid_flow/pressure-loss-from-fittings-expansion-and-reduction-in-pipe-size/
and
If something here looks relevant, post back.

The trick seems to be to get or estimate all the coefficients for the correct formula - the rest is math on a calculator or a spreadsheet.

What info & numbers do you have besides what you posted? From the first link it looks like we need nine, total.
IIRC, determining whether the flow is laminar or turbulent is important and almost certainly you need the pump curve.

Worst case, have your library borrow this
from another library.

Chunks of it are online but you need exact quotes to pull up the right section.

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Last edited by Wuzzat?; 03-27-2014 at 08:07 PM.

03-28-2014, 08:00 AM
Chris
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As far as I know you don't loose any pressure by reducing pipe size. You will however loose volume. When I get to my office I will post a sheet from nfpa 24 that shows what to expect for gpm at different pressures from different pipe sizes.

Don't know if any of that will help but the info won't hurt.

Sent from my iPhone using Home Repair

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03-28-2014, 08:27 AM
kok328
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Thanks guys. I'm not opposed to crunching numbers but, I don't have enough info to fill in the blanks.
I was looking for an easy answer but, ....
I didn't want to get into coefficient of drap using copper versus pvc versus etc....
How many bends, distance, etc .....

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03-28-2014, 08:57 AM
Chris
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Do you have access to put a pitot tube on it? If so that chart I was talking about will give you an easy way to see what GPM you are flowing.

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03-28-2014, 10:13 AM
Wuzzat?
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Quote:
 Originally Posted by Chris As far as I know you don't loose any pressure by reducing pipe size. You will however loose volume. When I get to my office I will post a sheet from nfpa 24 that shows what to expect for gpm at different pressures from different pipe sizes. Don't know if any of that will help but the info won't hurt. Sent from my iPhone using Home Repair
Water is incompressible so you can't lose volume but the delivered GPM may drop because the pressure dropped. The water entering the system must leave the system.
This is kind of a chicken and egg problem.
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03-28-2014, 10:28 AM
kok328
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Chris, anyway to make your charts bigger, I can't see them completely but, it looks like what I'm looking for.

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03-28-2014, 10:47 AM
nealtw
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Quote:
 Originally Posted by kok328 Chris, anyway to make your charts bigger, I can't see them completely but, it looks like what I'm looking for.
Save the picture to your computer, there you will be able to rotate it and enlarge it and print it.
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03-28-2014, 10:57 AM
Wuzzat?
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The oil pump in a car is positive displacement and with this kind of pump there may be no pressure loss. And if the pipe gets blocked the pump breaks.

I guess most water pumps are of other types (velocity pumps?).

http://www.engineeringtoolbox.com/classification-pumps-d_55.html

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Last edited by Wuzzat?; 03-28-2014 at 11:07 AM.