Both statements are correct; it is all about supplying source. Pump Handbook explains the phenomena in more detail; McNally should take note of that. And make sure that the reduced section is not smaller than the pump suction! (believe it or not, I just fixed such problem recently).
George
> These two sites contradict each other; McNally
> Institute says FOT at
> pump suction and The Pump Handbook (via Fluide
> Design) says it should be
> FOB. Any comments out there? Could the Pump Handbook
> actually be wrong?
>
>
>
http://www.mcnallyinstitute.com/CDweb/p-html/p015.htm
>
> "Make sure eccentric reducers are not installed
> upside down at the pump
> suction. The top of the reducer should go straight
> into the suction flange."
>
> "Use eccentric reducers rather than concentric
> reducers at the pump
> suction. Concentric reducers will trap air. Be sure
> the eccentric
> reducer is not installed up side down."
>
> "Be careful to install the eccentric reducer with
> the straight side up
> to prevent trapping air at the pump suction."
>
>
>
>
http://www.fluidedesign.com/download-free/guidel_pump_syst-extract.pdf
>
> "Always use an eccentric reducer at the pump suction
> when a pipe size
> transition is
> required. Put the flat on top when the fluid is
> coming from below or
> straight (see
> Figure 1) and the flat on the bottom when the fluid
> is coming from the
> top. This will
> avoid an air pocket at the pump suction and allow
> air to be evacuated."
>
> [This text is followed by a graphic showing a
> *flat-on-bottom* eccentric
> reducer directly connected to a pump suction with
> suction line coming in
> from the top (as if feeding the pump from a
> piperack). The image is
> credited to "The Pump Handbook published by
> McGraw-Hill.]
>
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