Elbows and Suction 2

[Milkboy]

Hi Group

I was recently searching for info on Suction Lift pumping aswell as getting good advice from engtips )

One bit of Info I found was regarding the suction line and I cant find it again.

I would like to know the recommended min distance of straight pipe at a pump suction before there in an elbow?

Is this the same for all pumps, overhung, double suction, etc?

TIA





-
Milkboy

 

[Scipio]

Recommended min distance is usually 5-10 pipe diameters to stabilize the flow pattern going into the impeller. It does vary from pump to pump, though, since some are more sensitive to prerotation or un-symmetrical loading than others.

One example would be a double-suction pump that has a vertical vane in the suction nozzle to split the flow between the two impeller eyes. If there's an elbow in the vertical direction (the most likely in the case of a suction lift scenario), you can actually put it right against the pump nozzle in some cases. If the elbow is in the horizontal direction, 10 diameters might not even be enough to prevent an uneven 'split' of the flow.

If space is an issue, however, you can get straightening vanes and prerotation vanes that will correct the hydraulics if you can't keep the elbow (or valve, or even a reducer if it's a large enough size change) away from the suction nozzle.

 

[pumpking]

In reality im sure you can get away with 5 diameters, but from a design point of view, pump manufacturers much prefer to have 10 diameters - it is always good, if installation allows, to go nearer this figure in case you do get problems