NPSHA affected by position of pipe irregularity?
NPSHA affected by position of pipe irregularity?
(OP)
Hi, we have a pump that's cavitating. Right before the suction inlet the piping has 2 45 degree bends welded together to gain about 2" of elevation. I know that there should be around 3-5 pipe diameters of pipe in a straight line before the suction inlet, but in this case it's about 0.5 pipe diameters. I would think moving this farther away from the pump would alleviate the cavitation, but I don't see anything in the calculation for NPSH that accounts for the position of this bend in the piping. Ideally, I know it'd just be best to get rid of the bend, but cutting a new outlet from the tank would be a lot more expensive. Thanks for any advice on this.





RE: NPSHA affected by position of pipe irregularity?
The turbulence and friction loss associated with elbows will reduce the NPSHa regardless of where they are located in the suction. But you want as close as you can get to laminar flow at the pump suction. This is why you want a straight run into the pump suction.
RE: NPSHA affected by position of pipe irregularity?
http://virtualpipeline.spaces.msn.com
RE: NPSHA affected by position of pipe irregularity?
RE: NPSHA affected by position of pipe irregularity?
RE: NPSHA affected by position of pipe irregularity?
http://virtualpipeline.spaces.msn.com
RE: NPSHA affected by position of pipe irregularity?
Suction pipe vortices and pre-rotation increase the NPSHR.
RE: NPSHA affected by position of pipe irregularity?
NPSHa is determined by system variables (friction loss, tank level, fluid temp, etc) Therefore vortices and pre-rotation are said to reduce NPSHa, not increase NPSHr.
RE: NPSHA affected by position of pipe irregularity?
RE: NPSHA affected by position of pipe irregularity?
Experts tell us that prerotation effects may also depend on the impeller geometry and specific speed.
There are cases where at low (partial) flow rates the NPSHR undergoes a drastic increase, an effect attributed to prerotation setting in.
In extreme cases, with low NPSHA, the system may develop noise and vibration, as if subjected to hammer blows.
RE: NPSHA affected by position of pipe irregularity?
RE: NPSHA affected by position of pipe irregularity?
http://virtualpipeline.spaces.msn.com
RE: NPSHA affected by position of pipe irregularity?
RE: NPSHA affected by position of pipe irregularity?
http://virtualpipeline.spaces.msn.com