NPSH-pump suction with compensation loop

[rob5377]

Hi All,

I was asked to review if existing centrifugal pump handle a new suction line arrangement. Pump used to "suck" water 0.7 meters below pump CL and now a compensation loop going 2.5 meters above pump CL was added. My concern is if i should consider 0.7 or (0.7+2,5) meters in static head in calculations. At the begining of suction line foot valve is installed so pipe will be kept flodded. I need it to be sure that in the system is enough NPSHA.

In my opinion during the start up a system will have to overcome 3,2 meters of static head at suction side so I considered this in calculations.

thanks
Rob

 

[BigInch]

I can't visualize this without a big chance for making a stupid guess. Can you save me the potential embarassment and attach a diagram?

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

 

[rob5377]

BigInch, it must have been my English
Attached sketch of the system. At the begining the suction line was without compensation but due to extended forces on the pump nozzle this compensation needs to be added.

 

[rob5377]

To be more specific this pit is inside big water reservoir. As shown on the drawing.

Thanks

Rob

 

[BigInch]

At least 3.2 There's more, so plus flow resistance of foot valve, the 4 ells around the goosneck plus all the pipe from the bottom of the riser to the pump suction flange. Once the gooseneck fills, then the -3.2 will cancel with the +3.2, but you still have the rest of those NPSH parasites still eating it up.

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

 

[rob5377]

Thanks BigInch. Yes I added friction losses of piping and fittings.

cheers