RE: Eccentric Reducers on Pump Suctions Redux - F OT/FOB

From: <G.>
Date: Sun Feb 27 2005 - 05:27:00 EST

One case I used FOB in pump suction is when the fluid is slurry like poly propylene and poly ethylene services. In this case invariably the fluid comes from the top as we want to avoid pocket.

Otherwise, FOT is always followed with 3D or 5D straight length in the suction pipe line.

GSN Murthy.

-----Original Message-----
From: Jacques Chaurette [mailto:jchaurette@fluidedesign.com] Sent: Saturday, February 26, 2005 5:17 PM To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Eccentric Reducers on Pump Suctions Redux - FOT/FOB I think that eccFOT will work in all cases will work since if gas accumulates at the top of the flat it will eventually move through the pump and be eliminated. If you use the ecc.FOB when fluid is coming from above it gives you the opportunity to eliminate the gas right from the start, in fact no gas can accumulate at the pump suction since it will normally rise up out of the suction pipe. Gas can be very hard to get rid of when it collects in flat spots this eliminates any collection possibility.

Jacques
www.fluidedesign.com

   Yes, I know, as I've read that (Pump Handbook) excerpt carefully, and    I've seen something similar reproduced elsewhere in standards over the    past 20 years or so.

   My point is that the fluidedesign.com image excerpt from "The Pump    Handbook" contradicts most other sources when it comes to flow coming    into a centrifugal pump from above and the proper orientation    installation recommendations for an eccentric reducer on a pump suction    (FOT vs. FOB).

   Where is entrained air/vapour going to collect after extended operation    in the visual scenario proposed by Figure 1 at    http://www.fluidedesign.com/download-free/guidel_pump_syst-extract.pdf
<http://www.fluidedesign.com/download-free/guidel_pump_syst-extract.pdf> ?

   I'm assuming that there will be some turbulent flow characteristics due    to the change in direction through the elbow (and also any upstream    combination of X-Y-Z axis piping) and that air/vapour would naturally    collect in the high "cavity" point of a FOB reducer. Then, this    collection of air/vapour could slowly impinge on the impeller or let    loose all at once. This IS fluid dynamics analysis, so event prediction    is one of those things that cannot be reliably measured.

   Am I wrong in my interpretation or am I going straight to pump hell for    being a heretic (or, even worse, condemned worldwide as being a moron in    the piping design community)?

   Maybe some inexperienced draftsman made a drawing mistake and it wasn't    caught by the editors for all these years.

   And as usual, I'll add the caveat that I'm just asking questions since    the only dumb question (within reason) is the one you didn't ask.

   Paul

   Jacques Chaurette wrote:

   > The Pump Handbook actually recommends both situations, depends on whether the fluid is coming horizontal or from the bottom (FOT) or if it is coming from the top (FOB).


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Received on Sun Feb 27 05:27:00 2005

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