headloss gravity flowing through pump and/or through ARV?

[chileheadcraig]

We are evaluating a scenario where the check valves would be replaced with spool pieces and flow would be allowed to flow backwards through the high service pump in order to facilite drainage of a reservior in emergency situations. My question is how should I approximate the headloss due to reverse flow through the pump? I am modeling this in WaterGEMS and would like to represent it as a k-value if its a feasible approach.

Another alternative is to remove the "guts" from several 12" ARVs in the main line to allow drainage to the nearby ground surface. I would also like to estimate k-values for these as well.

Thanks much for any advice.

 

[BigInch]

You probably don't want reverse flow through the pump, if you also intend to run it normally sometimes. Starting while reverse flowing can cause a lot of problems. At least leave a block valve on the discharge with an interlock to prevent starting if that valve is open. That might also require a recirculation valve to start while the block valve is closed.

You'll have to find out how to make 4th quarter pump curves to predict reverse flow heads. See Centrifugal Pump Design by Stepanoff.

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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/

 

[chileheadcraig]

This is not a normal operating condition. They will have to intentionally removed check valves, install spool pieces and then allow it to reverse flow. The flow will be stopped and check valves replaced before the pumps are allowed to return to normal operating conditions.

I am seeking head losses from gravity flow. will generating a 4th quarter pump curve give me this? You can even assume that the motors are detached if you like. There is no power being input in this evaluation. Thanks for offering advice.

 

[BigInch]

Yes detach the motors or you might generate electricity with them.

Sounds easier to drain through the valves. You could use k values, if you had a way to estimate what they might be with the guts out. Rough it in with an orifice flow estimate from the remaining x-sectional area (???).

**********************
"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/

 

[Artisi]

If the only loss in the system is thru'the "pump" then it might be worth knowing whereas, if the loss thru'the "pump" is only a minor part of the total losses is it even worth a consideration.

Also, the loss thru the pump will depend on the pump type, and be aware that the reverse runaway speed can be a lot higher than the normal operating speed so critical speed could become an issue.