head loss in water distribution system 4

[davemul1]

I am working on a project that has two existing submersible well pumps. These pumps discharge directly into the water distribution system. How do I compute the head loss from the pumps to the water towers?

 

[cvg]

unless you have a separate transmission main, you will need to do a network analysis to figure out the system curve for the pumps. If a separate main, then it is simply length of main times head loss per foot plus minor losses. Use Hazen Williams hydraulic tables to estimate the headloss per foot

 

[SteveWag]

I have worked in some older cities with water systems 75 to 90 years old and found cast iron pipes with a c-factor of 45 tp 50. I've also seen a many pumps that were not working as designed because of higher than anticipated discharge pressures.If the pumps are more than 300 GPM I would do a system test rather than relying entirely on calculations. Place a pressure recorder near the point of connection and see what a weeks worth of data looks like. Then with the recorder in place, open a nearby hydrant so as to produce a flow that the pumps are designed to produce. The recorder will show a drop in pressure. If possible stick some gauges nearby and record flow and non flowing pressures. Try another nearby hydrant and check pressures. The difference between the static (non flowing) and the flowing pressures will be very near the pressure needed to put the same flow into the system. Convert everything into feet ASL and go to work.

Steve Wagner

 

[cvg]

Stevewag - good idea!

Any calculation should be calibrated to actual field measurements if possible. Hydrant tests should be done at a few locations between the pump and the tank. They should also be done at different times of the day and especially during peak flow times. Residual pressures should be compared to what the computer analysis predicts. Roughness factors, usage demand and flow rates should be adjusted as necessary to calibrate the model.

You should also look at any data you can on the existing pumps such as power consumption, flow rates and compare it to the spec values to determine if they are operating as expected.

 

[RWF7437]

davemul1,

Is you question how to calculate head loss with one pump running or both pumps running ? Also, how are these pumps connected through the system and to the tank(s)?

While Hazen-Williams is widely used, my own preference is for the Darcy Weisbach equation. The free program, EPANET, can be used to do the analyses for you.

good luck

 

[davemul1]

RWF7437,

I'm trying to calculate the head loss with one pump running and both pumps running. The pumps discharge directly into the water main system. The mains are connected directly to the towers. There are not dedicated lines from the pumps directly to the towers.

 

[RWF7437]

You need to calculate the system head curve for the system you've described for a range of flows from whatever you think is the lowest to whatever you think may be the highest probable flow. Then plot the system head curve and the pump curves. Add the ordinates of the two pump curves to get the operating curve for both pumps running ( in parallel ?). The points where these three curves intersect is the operating point for the system with one, the other, or both pumps running. You can find examples of this procedure in any good hydraulics text and in many pump manufacturer's catalogs or on their websites.

good luck

 

[RWF7437]

Correction:

See: Resources, Tools and Basic Information for Engineering and Design of Technical Applications!
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Resources, Tools and Basic Information for Engineering and Design of Technical Applications!
Pumps in Parallel or Serial Connection
For pumps in serial - add heads, for pumps in parallel - add flowrates

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Pumps can be arranged in serial or parallel to provide additional head or flowrate capacity.
Pumps in Serial - Heads Added

When two (or more) pumps are arranged in serial, their resulting pump performance curve is obtained by adding heads at the same flowrate.

pumps in series

For two identical pumps the head will be twice the head of a single pump at the same flow rate.
Pumps in Parallel - Flow Rate Added

When two or more pumps are arranged in parallel, their resulting performance curve is obtained by adding their flowrates at the same head.

pumps in parallel

For two identical pumps the flow rate will be twice the flowrate of a single pump at the same head.

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Related Topics

* Pumps Pumps and piping systems ....

Related Documents

* Centrifugal Pumps An introduction to Centrifugal Pumps
* Static Pressure and Pressure Head in Fluids Static pressure and pressure head in fluids
* System Curve and Pump Performance Curve To select a proper pump for a particular application it is necessary to utilize the system curve and the pump performance curve
* Alternating Pumps Secure the system and achieve equal wear by alternate pumps in parallel

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[BigInch]

its easier to read if you just link to the url.

http://virtualpipeline.spaces.msn.com

 

[Artisi]

Is this system currently in operation or is it under modification or reconstruct?

 

[davemul1]

Artisi,

It is currently in operation.

 

[Artisi]

The total head across the pumps is the discharge pressure minus the inlet pressure - all you need to do is measure the pressure at the pump discharge flange or close to it and measure the pump submergence - this will give you a pretty good idea of what the pump head is. If you now measure the static head, water level in the sump to the highest point on the discharge side the difference between total head and static head is the friction head and exit losses etc in the pipe work system.