Pressure Drop Correlation with Fluid Loss
Pressure Drop Correlation with Fluid Loss
(OP)
Hi Everyone,
I have an underground water main that is quite old. It is an 8 inch diameter ductile iron pipe and is approximately 200 ft long. Wanting to see if it is still fit for service, we pressurized it to 150 PSI and left it over night. Next day, we lost 25 PSI. So 25 PSI loss over 24 hours.
Probably too big of a pressure drop to attribute to temperature fluctuations right? .. so Clearly there is a leak in there somewhere.
Are there any rules of thumb to use to see how much water we are actually losing?
Thank in advance,
I have an underground water main that is quite old. It is an 8 inch diameter ductile iron pipe and is approximately 200 ft long. Wanting to see if it is still fit for service, we pressurized it to 150 PSI and left it over night. Next day, we lost 25 PSI. So 25 PSI loss over 24 hours.
Probably too big of a pressure drop to attribute to temperature fluctuations right? .. so Clearly there is a leak in there somewhere.
Are there any rules of thumb to use to see how much water we are actually losing?
Thank in advance,





RE: Pressure Drop Correlation with Fluid Loss
RE: Pressure Drop Correlation with Fluid Loss
Best method at this point would be to pump in more water and see how much volume it takes to raise the pressure to 150 again.
Rule of thumb is to first measure what you pump into and correlate that to the calculated inside volume of pipe. At least that way you are less likely to contain a lot of air.
RE: Pressure Drop Correlation with Fluid Loss
So you're still thinking that 25 psi could be related to temperature drop?
Any good way to account for temperature changes?
RE: Pressure Drop Correlation with Fluid Loss
Probably 1 or 2 degrees C
If its ductile Iron is this push fit pipe? It might just have expanded a mm or two?
a water main that is this tight is pretty good. Many would lose all the pressure in a few minutes
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Pressure Drop Correlation with Fluid Loss
RE: Pressure Drop Correlation with Fluid Loss
http://www.nwpipe.com/wp-content/uploads/2014/10/J...
Q: What is the purpose of the “testing allowance” in ANSI/AWWA C600?
A: ANSI/AWWA C600 “Installation of Ductile-Iron Water Mains and Their Appurtenances” requires that newly installed Ductile Iron water mains be hydrostatically tested at not less than 1.25 times the working pressure at the highest point along the test section and not less than 1.5 times the working pressure at the lowest point of testing.
After the air has been expelled and the valve or valves segregating the part of the system under test have been closed, pressure is then normally applied with a hand pump, gasoline-powered pump, or fire department pumping equipment for large lines. After the main has been brought up to test pressure, it is held at least two hours and the make-up water measured with a displacement meter or by pumping the water from a vessel of known volume. The make-up water is called the “testing allowance,” and the allowable amount is a function of length of pipe tested, nominal diameter of the pipe, and the average test pressure. The hydrostatic pressure test helps to identify damaged or defective pipe, fittings, joints, valves, or hydrants, and also the security of the thrust restraint system.
The “testing allowance” is not a “leakage allowance.” Properly installed Ductile Iron Pipelines with properly assembled joints are bottle-tight and do not leak. The “testing allowance” is, however, a practical measure used to maintain the pressure, which might actually drop because of factors other than leakage, including trapped air, absorption of water by the cement lining, extension of restrained joints and other small pipe-soil movements, temperature variations during testing, etc.
(Issue: Spring/Summer 2002)
http://www.dipra.org/ductile-iron-pipe-resources/f...
RE: Pressure Drop Correlation with Fluid Loss
RE: Pressure Drop Correlation with Fluid Loss
A 25psi drop on a 150psi line tells me youve still got some air in this pipe.
RE: Pressure Drop Correlation with Fluid Loss
Thanks again!
RE: Pressure Drop Correlation with Fluid Loss
Now get all that air out of there and see if it holds.
RE: Pressure Drop Correlation with Fluid Loss