Hydraulic Grade Line Conversion
Hydraulic Grade Line Conversion
(OP)
Help!!
I have a flow test from a local water district in Southern California that provides the following information:
HGL - 830
Residual Pressure - 90
Outlet Size (inches) - 4
Outlet Coefficient - 0.9
Pitot Pressure - 40
Observed Flow - GPM - 2717
My question is how do I convert the HGL of 830 to a static pressure? I have not run into this situation before and I'm curious. Every other flow test I have recieved has given static in lieu of HGL.
Thanks!!
Canman
I have a flow test from a local water district in Southern California that provides the following information:
HGL - 830
Residual Pressure - 90
Outlet Size (inches) - 4
Outlet Coefficient - 0.9
Pitot Pressure - 40
Observed Flow - GPM - 2717
My question is how do I convert the HGL of 830 to a static pressure? I have not run into this situation before and I'm curious. Every other flow test I have recieved has given static in lieu of HGL.
Thanks!!
Canman





RE: Hydraulic Grade Line Conversion
RE: Hydraulic Grade Line Conversion
You need the elevation where the test was perfomed.
HGL = Pressure*2.31 + elevation
Given the residual pressure was 90, the elevation is not more than 620.
The district should have given both static and residual pressures in the same units.
Hydrae
RE: Hydraulic Grade Line Conversion
RE: Hydraulic Grade Line Conversion
With all respect, I think the numbers are in psi,
to get 2717 gpm out of single 4 inch nozzle, that will be 69 ft/sec, and a residual of 90 psi is about right to get that kind of flow.
Hydrae
RE: Hydraulic Grade Line Conversion
The following are definitions pulled right off the internet. In order for these formulas to make sense, one needs to understand specific meaning of the following terms. (Most are pretty basic but a couple are generally misunderstood.)
STATIC PRESSURE
Pressure reading before water flows.
RESIDUAL PRESSURE
Pressure reading while water is flowing (from an outlet other than the flow outlet.)
PITOT PRESSURE
Reading taken by a pitot gauge inserted into the center of the flowing outlet, at a distance away from the lip of the outlet of about half the nozzle's diameter.
RE: Hydraulic Grade Line Conversion
Canman
RE: Hydraulic Grade Line Conversion
If there is truely just a 2 psi drop at 2717 gpm, yes the 18k would be about right. Three ways I can think of that could happen. The following objects should be within 300 ft as a single connection or 1000 ft as a looped connection
Is the 12" near a larger pipe say 30" or greater,
Is it next to a reservoir?
Is it near a prv, the prv will open up to maintain a constant downstream pressure at any flow up to 80% of the wide open pressure drop of the valve, thus giving a false calculation of flow at 20 psi. (this one I most suspect)
Hydrae
RE: Hydraulic Grade Line Conversion