RE: eccentric reducer

From: <Steve>
Date: Tue Sep 21 2004 - 05:36:00 EDT

Hi Prem
normally it doesn't matter.

Two cases where it may:

1. Suction lift out of an open pit into a horizontal axis pump. If the suction velocity is low and the lift is large and the flat side is down, then there is the possibility of trapping air at the top of the pipe which can theoretically cause problems in maintaining prime. Normally flat side at top in this application, and arguably for well aerated slurries such as flotation overflow streams.
2. Solids or slurry piping. Heavier solids normally travel along the bottom of a pipe. If the flat is at the top, the solids may have difficulty climbing up the incline at the bottom of the reducer. Some argue this can affect NPSH. It is true that the heavier (larger) particles will abrade the incline and result in premature failure. Normally flat side at bottom.

From a hydraulic perspective, a concentric reducer seems preferable as the velocity profile presented to the impeller eye is axisymmetric, unless the solids gradient is really high. However some well-respected engineers prefer a reducing bend at the suction, so who knows?

Cheers

Steve

-----Original Message-----
From: Premkumar, Soundrarajan [mailto:spremkumar@mcdermott.com] Sent: Tuesday, September 21, 2004 3:13 PM To: PipingDesign (E-mail)
Subject: [PipingDesign] eccentric reducer

hi everyone,

why we use eccentric reducer in pump suction and in which case we use flat side up and flat side down?

prem

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