Calculating Flow @ a given pressure
Calculating Flow @ a given pressure
(OP)
I'm trying to find a standard flow rate in gpm for PVC pipe on a city line at a give psi. I can calculate gpm from velocity, and can find pressure drop, but am unable to find a table or equation for this calculation





RE: Calculating Flow @ a given pressure
RE: Calculating Flow @ a given pressure
RE: Calculating Flow @ a given pressure
try this web calculator
http://www.lmnoeng.com/Pipes/PipeNetwork.htm
RE: Calculating Flow @ a given pressure
If you knew, for example, the pressure at some other point downstream (and any elevation changes) and the equivalent length of pipe between the points (equivalent including other minor losses such as changes in direction, etc.), you could figure out the velocity by way of the Darcy formula which relates pressure drop or head loss (due to friction) to velocity.
If you're simply looking for maximum "acceptable" flow rates through PVC pipe, etc. of different diameters, then you need to look at charts which are derived from the Darcy formula (or do it all manually, or use a computer program--someone on the previous thread had a link) where you can attempt to limit the pressure drop to something reasonable (say 4'/100') or the velocity to something reasonable (say 8 fps for 8" and smaller piping) and then see what the gpm is. You can obviously pump more or less water though the same size pipe, it just changes the pressure drop through the system. The losses may or may not be acceptable depending on the pressure you need at the point you're trying to to get the water to.
I hope that made sense. Someone else may be able to explain better.
RE: Calculating Flow @ a given pressure
Try this website:
http://www.martindalecenter.com/Calculators4.html
and go to the Fluid Dynamics & Mechanics section.
RE: Calculating Flow @ a given pressure
To understand and accept that what you stated is wrong, refer to either Crane's Tech Paper #410 or Cameron's Hydraulic Data book. There, you will find the basic relationship of fluid flow in a pipe. The Darcy-Weisbach equation is what defines the flow of fluid in a pipe and it requires that you define the allowable pressure drop (the driving force, or head) in order to obtain the related flowrate of liquid in the pipe. Cameron gives you tables of expected water flowrate in a variety of pipes with a variety of pressure drops. You can create your own similar table for PVC pipe.
You need a Driving Force to obtain a flowrate, not a simple pressure value. Fluid flow is analogous to the flow of electricity: you don't have coulombs flowing because of voltage; you obtain coulomb flow due to the existance of a voltage drop.
And by the way, there is no "standard" gpm. Volume for incompressible fluids (such as water) is simply volume. You don't get into "standard" conditions until you mess with compressible fluids (gases or vapors).
RE: Calculating Flow @ a given pressure
I assume you're trying to set-up standard capacity tables for various sizes of plastic pipe at various inlet pressures given a fixed terminal pressure
Go to the link below and order - Performance Pipe (Plexcalc) CD-ROM. – It's free.
http://www.hdpe.com/Freebies.shtml
The CD has a complete polyethylene industrial and municipal piping catalog. Also includes an engineering manual on properties, design and installation. Along with this you get Plexcalc to assist in your flow calculations, design and construction.