NPSHr for Vertical 3 Stg. Pump 1

[DaEarl]

Greetings,

I am working on resolving suction problems on a Byron Jackson 3 stg. Vertical Turbine. The datasheets that I have at my disposal include a pump curve without a NPSHr curve. I was referred to other paperwork where the NPSHr was given for the design flowrate. Two values are given: 1)NPSHr @ Impeller Eye=16 ft., & 2)NPSHr @centerline of suction nozzle=-2 ft. The question is which value is the right one to use? From study of the dimensions of the turbine, it is clear that the distance from the suction nozzle to the impeller eye is 18 ft. Any help is appreciated.

 

[JJPellin]

You could use either location as your reference. The most important thing is that you calculate the NPSH required and the NPSH available using the same reference so you have an accurate evaluation of the NPSH margin. Personally, I prefer to see all suction head numbers referenced to the centerline of the impeller. A negative NPSH required seems kind of nonsensical. If this pump is in an atmospheric sump, then the advantage of atmospheric pressure makes the NPSH margin less important than the minimum submergence requirement for the pump. In other words, even if you suck the sump completely empty to the impeller inlet, you would still have 32 feet of NPSH available (less vapor pressure), but the pump would be ingesting air and could be damaged long before you got to that point.

 

[rmw]

I agree with JCPellin in that minimum submergence might be the governing factor.

Can you give the type and series of the pump? I have some serious BJ technical books and would like to look it up.

rmw

 

[DaEarl]

rmw,

Thanks for the post. The BJ pump is a 2000 VLT 3 stg. turbine. 1200 RPM, 20" HQ-"L" Imp. Vertical Turbine.
I also have a note here that states a minimum submergence of 60". Thanks for the help.

Kyle