Fluid Pressure in Pipe
Fluid Pressure in Pipe
(OP)
I have 1,075 gpm of water flowing through an 8" pipe at a velocity of 7.05 ft/s and a pressure of 75 psi. I need to branch off that 8" line to divert enough flow to reduce the pressure from 75 psi to 65 psi. How do I calculate the amount of flow to divert to reduce the pressure in the main line? Any help would be appreciated.





RE: Fluid Pressure in Pipe
New flow rate= measured pressure/rated pressure x 0.5 x rated flow. divert 65psi/75psi x 0.5 x 1075 GPM = 465 GPM
Please check with others to follow
RE: Fluid Pressure in Pipe
Let's say you had a centrifugal pump feeding this line with 1075 gpm and 75 psig being its operating point. If you wanted to drop the pressure to 65 psi by 'bleeding' off water, you'd need to look at the pump curve to see what flow you needed to put through the pump to bring the discharge pressure down to 65 psi from 75 psi. The difference between that flow and 1075 gpm would be the flow through your new side line. If the curve is steep, the additional flow might be small, if the curve is quite flat, you could be talking a lot more flow.
Let's say on the other hand this 8" water line comes off a 24" distribution header. Practically speaking, you might not be able to draw off each additional water to drop the pressure to 65 psi in this system.
Let's say the 8" line is actually a long pipeline with the delivery pressure being 75 psi when flowing 1075 gpm. Depending on the length of line and supply pressure device (pump, etc), you might not need to flow very much more water to drop the pressure simply due to additional friction losses.
We need a more complete description of your system to give you an idea how to calculate the necessary flow.
RE: Fluid Pressure in Pipe
Good luck,
Latexman
RE: Fluid Pressure in Pipe
Thanks.
RE: Fluid Pressure in Pipe
If you already had the intention for a bypass, why not consider a pressure regulating valve or an adjustable choke valve for the by-pass line, if your centrifugal pump cannot be replaced.
This will allow you a great extend of flexibility to regulate the line pressure in relation to your downstream process.
Otherwise, you can also trim down on the pump impeller to the required pumping rate/dp. Check with the pump specialist.
RE: Fluid Pressure in Pipe
Good luck,
Latexman