Eccentric Reducer Position when Fed from Above?

7/9/2024

NFPA 20 is pretty clear on the orientation of the eccentric reducer on the suction (upstream) side of a fire pump.

But the diagrams seem to suggest that the diagonal slope (not the flat side) of the eccentric reducer is always on the bottom.

Is this true even when the supply is being fed from above?

For instance, we often have a stub into a fire pump room from the floor, then a vertical backflow preventer, then the feed comes vertically-down and to the fire pump.

Which way is correct for the eccentric reducer when the feed is from above?

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10 Comments

Pete H

7/9/2024 07:07:33 am

Pretty sure even if the feed is from above, you're still under guidance to put the flat side of the eccentric reducer. I think just being eccentric might be enough to reduce air pocket development. It still has to go 10 pipe diameters before the suction elbow which should get it to a horizontal feed.

Basing this on:
NFPA 20 (2016 ed.):
Figure A.4.15.6 - the top part of the image on the "right" side, doesn't show whether the feed is from above or below, because it still has to go horizontally into the suction of the pump.

Plus that detail also establishes you might have an elbow or tee at your point of suction before, for example if you used vertical piping to accomplish your 10 pipe diameters due to a smaller pump room, you'll still be coming in from above, you'll still have your eccentric reducer (if required) in the normal orientation (flat on top, diagonal on bottom).

Take with grain of salt, but this is where I'm landing.

Pete H

7/9/2024 07:15:23 am

"under guidance to put the flat side of the eccentric reducer on top" is what I meant to type in that first sentence.

Anthony

7/9/2024 07:35:13 am

If the feed is vertical it drops to a 90 then goes into the eccentric reducer. Don't put the eccentric reducer on the vertical drop with a 90 straight into the pump. Confirm with your pump rep if you need further guidance.

7/9/2024 07:40:06 am

No the eccentric reducer wouldn't be on the vertical; it'd still be horizontal going into the pump.

Basically comes from above, 90-degree elbow, OS&Y suction, eccentric reducer, then suction flange of pump.

All of it is still in the 'plane' of the pump, but wanting to know the proper way to orient the eccentric reducer.

Dan Wilder

7/9/2024 07:58:14 am

I've seen and done this before with the pump MFG & Rep approval....while not specifically called out in NFPA 20, this is allowable.

Here is one of the articles on it by the US Fire Administration....

https://www.hsdl.org/c/abstract/?docid=720893

I'll see if I can find the MFG sheet on it as well.

Glenn Berger

7/9/2024 08:15:42 am

With the eccentric reducer being placed in the horizontal piping supply to a fire pump, it is always flat on top.

I too was confused by the comment on the proposed orientation of the reducer to the fire pump.

Franck Orset

7/9/2024 08:37:20 am

For a very long time, I was pretty sure that the flat bottom was always on top (as it is the only drawing indicated in NFPA 20). And I discovered recently that I might have been wrong for several decades, as I found several other technical documentations stating that it was true only if the water was coming from the side or from below.
If coming from top, it is normally to be installed with flat on bottom) (or with a concentric reduction), as indicated in the document from Dan :

When the pump is fed from below or the side from
an underground water main, the eccentric reducer must
be installed with the ”flat side” on the top, parallel to
the floor. This arrangement prevents air being trapped
in the upper portion of the fitting.

In those configurations where the fire pump supply comes from above, such as is the lower elevations
of a basement or from an elevated tank, the eccentric reducer may be installed with the “flat side” down,
parallel to the floor. When the water supply is delivered from above, any trapped air can be bled off at the
top of the pump casing while the system is filled with water.

In the document, there is a picture with the correct installation (flat at bottom) as water is top fed...

Other technical informations (samples) on this issue:

https://www.theprocesspiping.com/pumps-suction-piping-eccentric-reducers-straight-lengths/

When the source of supply is above the pump, then the eccentric reducers must be placed with the flat side down. When the source of supply is below the pump, then the eccentric reducers must be placed with the flat side up.
In case of long horizontal pipe runs, air pockets are avoided by installing the eccentric reducer with the flat side up.

https://www.pumpsandsystems.com/reducer-fittings-decrease-pipe-size-avoid-failure-first-two-parts

Eccentric convergent reducers are normally used for horizontal installations where there is potential for air vapor accumulation. The flat side shall be located on top, unless the inlet (suction) line approach from above, in which case either a concentric reducer or eccentric convergent reducer (with the flat side on the bottom) should be used.

Franck

7/9/2024 08:39:51 am

https://www.linkedin.com/posts/danvolsky_check-your-pumps-eccentric-reducers-installation-activity-7084434651687075840--DVV/

Jack G

7/9/2024 10:33:03 am

This was discussed on the Meyer website 11/18/2020. 13 comments I believe.
NFPA 20 is clear when the supply is horizontal or from below.
The pump handbook is vague.
The hydraulic institute recommends the flat part be on the bottom, with the reduced outlet on the top of the fitting/ elbow.
Mechanical pumps when supplied from above have the flat spot on the bottom( vertically)

Jack G

7/9/2024 04:49:34 pm

Another thing to consider are automatic air releases at the top of standpipes, and on individual floors of wet systems in addition to what’s required.
I ve even added them to my pump rooms with flow meters and bypasses. Trapped air can bring a world of hurt to your new sprinkler systems !

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Eccentric Reducer Position when Fed from Above?

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