Pressure Drop at Pipe Junction
Pressure Drop at Pipe Junction
(OP)
I calculated the line resistance and matched the system curve with the pump curve, but I found a mysterious 20 psig drop in the system that cannot locate. I'm guessing it is at the junction with the other pipe the line discharges into but I can't find a good equation to calculate the drop.
The line looks like this
-------------------------------> 8", Pstat = 32 psig, 5 ft/s, water
^
|
|
|
3", Pstat = 24 psig, 5 ft/s, water, Velocity pressure ~ 26 psig
Can this junction create a 20 psig resistance in the 3" line? The 3" line comes into the 8" line at a right angle.
The line looks like this
-------------------------------> 8", Pstat = 32 psig, 5 ft/s, water
^
|
|
|
3", Pstat = 24 psig, 5 ft/s, water, Velocity pressure ~ 26 psig
Can this junction create a 20 psig resistance in the 3" line? The 3" line comes into the 8" line at a right angle.
-Mike





RE: Pressure Drop at Pipe Junction
RE: Pressure Drop at Pipe Junction
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pressure Drop at Pipe Junction
The pump discharge is 148'head at 120 GPM on the 3" line. After 114' of pipe, a check valve, butterfly valve, a globe valve, 6-90 bends, and a 20' elevation, the pressure drop is 11.1 psig (25.6 ').
-------------------------------> 8", Pstat = 32 psig, 5 ft/s, water
^
|
|
|
3", Pstat = 52.9 psig, 5 ft/s, water, Velocity pressure ~ 26 psig.
The velocity pressure I had to take into account since the flow is going perpendicular to the 8" pipe. Did I do this wrong or am I on the right track?
-Mike
RE: Pressure Drop at Pipe Junction
Good luck,
Latexman
RE: Pressure Drop at Pipe Junction
-Mike
RE: Pressure Drop at Pipe Junction
What size hole did you cut/drill into the 8" line where you welded the 3" line?
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Pressure Drop at Pipe Junction
I'm going to test the check valve for a large pressure drop tomorrow.
-Mike
RE: Pressure Drop at Pipe Junction
Good luck,
Latexman
RE: Pressure Drop at Pipe Junction
-Mike
RE: Pressure Drop at Pipe Junction
Good luck,
Latexman
RE: Pressure Drop at Pipe Junction
my question basically came down to this: can the 8 inch line cause a decrease in flow so that the 3" line is restricted to the point of creating 20 psig extra resistance. Basically think of the 8" line's flow as creating a nozzle at the 3" line's discharge.
i want to make sure that it's possible to create this large of a pressure drop since there seem to be no equations to model this, short of CFD.
-Mike
RE: Pressure Drop at Pipe Junction
Good luck,
Latexman
RE: Pressure Drop at Pipe Junction
-Mike
RE: Pressure Drop at Pipe Junction
Good luck,
Latexman
RE: Pressure Drop at Pipe Junction
However, the installation may have been bad, for example, if the 3 inch pipe protrudes into the 8 inch pipe by 7-1/2 inches, then you have a big restriction there, and all looks well from the exterior. There are numerous other errors that could cause high pressure drop in the line, about as many as you can imagine. This kind of poor installation work should be rare, but I have seen worse.
RE: Pressure Drop at Pipe Junction
You can also model your system in software such as PIPE-FLO or Crane Flow of Fluids to help troubleshoot.
An extra 20 psi drop is pretty large, so you may have a problem with partial pluggage. I once found a large bolt lodged between the seat and disc of a 150# steam pressure control valve at the mill I used to work at, and massive pluggage of orifices on a steam dryer that reduced steam flow by 25%.
You get what you inspect, not what you expect.
Jeff
RE: Pressure Drop at Pipe Junction
Do you have or have you used Crane Flow Of Fluids software?
I am just looking into it now. Your suggestion in response to the post is excellent. I am considering getting my own copy, I just want to get a few opinions first.
Regards,
SNORGY.
RE: Pressure Drop at Pipe Junction
I'd recommend you download the demo and play with program to see if you like it. I also recommend looking at other programs to do a comparison to see which one best fits your needs.
Jeff
RE: Pressure Drop at Pipe Junction
I will do exactly that this weekend in between activities in my "other line of work".
Considering what I think of Crane TP-410, I have no doubt that the software is good. Buying it sight unseen wouldn't scare me.
Regards,
SNORGY.
RE: Pressure Drop at Pipe Junction
The pressure drop seems high for a tee or stub in connection but if the cut-out on an O-Let was much smaller than the nominal 3" size (which is not uncommon) then that might be a possible source of the problem.
RE: Pressure Drop at Pipe Junction
thanks for the responses
-Mike
RE: Pressure Drop at Pipe Junction
Keith Cress
kcress - http://www.flaminsystems.com