Stright Run of pump suction pipe

[DESUB]

Straight run of Pump suction pipe is 4x suction pipe dia 'D' (BB3 pump, 500m3/hr, 200m diff head, npshr 2m, npsha 4m, 16" suction pipe) Pump vendor asks for 8D. Due to space limitations we can not go beyond 4D. Is elbow with vane straightener will be useful solution?

 

[rmw]

He wants that distance to get the turbulence of the turn away from the inlet of the pump.

While vane straighners might or might not reduce the turbulence (variety of factors involved) they would be a flow restriction, and would add additional resistance to the NPSHr calculation.

Since it appears that you have plenty of NPSHa, then this should not be a problem. You need to check the pump curve throughout the operating range for this.

Meanwhile, if you are interested in vanes, google the words "Cheng Vanes",

Note that vanes are designed velocity specific, so if your flow is going to be up and down the curve, you might not want to do this.

I would just use a larger elbow, and then transition back with an eccentric reducer with the flat side up and horizontal.

rmw

 

[rzrbk]

With the low NPSHr, I am guessing this is a double suction pump. (side or top suction) If this is the case, the vendors concern is probably with unequal flow to each side of the impeller. This can rusult in higer pressure on one side of the impeller causing axial shuttling, excess vibration, reduction in allowable flow range, etc.

In this case a vane straightener in the suction line after the elbow, or vanes that put extra rotation on the fluid just upstream of the last elbow should help.

Another way to reduce the straight run required is to make the last elbow (closest to the pump)turn perpendicular to the shaft. In this way, if more liquid is thrown to the outer radius of the elbow, flow to each side of the impeller is still somwhat uniform.