Vertical Reducer in Before Vertical Inline Pump?

7/14/2021

Can I install a concentric reducer in the vertical position and a 90 on the suction side of a vertical inline pump?

The feed is coming from above the pump, and we don't have space for a 90 and an eccentric reducer.

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11 Comments

JohnF

7/14/2021 08:08:59 am

use a reducing elbow

schulman

7/14/2021 08:11:24 am

NFPA 20 has some pretty good diagrams of the dimensional requirements for distance from fittings and orientation of fittings leading into the suction side of a pump. You should be able to find info that informs on your situation ...

Casey Milhorn

7/14/2021 08:30:03 am

I've done it before and I can't think of any restrictions for this scenario. but as Schulman said, NFPA 20 is fairly clear on fittings and dimensions.

Jesse

7/14/2021 08:30:24 am

Look at the annex material in NFPA 20. I think its A4 or somewhere there.

Glenn Berger

7/14/2021 09:05:26 am

4.16.6.4 requires the use of eccentric reducer where the suction pipe and pump suction flange are not of the same size.

Your request to use a concentric reducer in the vertical actually sounded correct, but look at 4.16.6 for guidance.

Jay

7/14/2021 09:13:09 am

2019 NFPA20: 4.16.6.4 Eccentric Tapered Reducer or Increaser.

Where the suction pipe and pump suction flange are not of the same size, they shall be connected with an eccentric tapered reducer or increaser installed in such a way as to avoid air pockets.

Craig S

7/14/2021 09:35:53 am

Like others have said, you should be using an eccentric reducer per NFPA 20, 2013, 4.14.6.4. As far as I am aware, eccentric and concentric reducers are the same length, so you should be fine there. Vic's #50 and #51 are both the same length, I would assume other manufacturers would be the same.

Franck

7/14/2021 11:05:05 am

That's an interesting configuration (never met so far).

The eccentric reduction is only necessary to avoid the air pocket when the reduction is installed horizontally before the pump suction flange.

The flat section should be put on top when the water is coming from below or straight (as in most installations, and as indicated in the NFPA 20 sketch)
The flat should be put on the bottom when the fluid is coming from the top (which is not indicated in NFPA 20 and is a quite common misinstallation).
Please have a look at :

https://www.enggcyclopedia.com/2011/12/pumps-suction-piping-eccentric-reducers-straight-lengths-piping/

for more information (nice sketch and explanation).

In your case, if the elbow is just before the pump, the reduction before the elbow and the pipe/reduction/elbow installed in a vertical plane perpendicular to the fire pump, you can use a concentric reducer (no possible air accumulation before the pump).
If you want a better laminar flow, to limit cavitation, I would suggest to put the reduction as far as possible from your elbow.

You can also use an eccentric reduction, but it would be of limited effect in your case, and would need to be installed with the reduction part facing your pump (and flat part, opposite), as the water will be coming from above the pump.

Jay Richardson

7/14/2021 11:54:06 am

In regards to: If you want a better laminar flow, to limit cavitation, I would suggest to put the reduction as far as possible from your elbow.
The reduction typically needs to be at the pump suction flange due to: 4.16.3.3 The size of that portion of the suction pipe located
within 10 pipe diameters upstream of the pump suction flange
shall be not less than that specified in Section 4.28.

Peter

7/14/2021 03:39:47 pm

This was my thinking as well. NFPA 20 requires 2 things: (1) certain pipe size 10 suction diameters upstream of the pump and (2) that you use an eccentric reducer for sizes that aren't the same from the pump suction flange to the suction piping. If your suction piping needs to be 6" (say a 750GPM pump), adding a 4" or 5" 90 degree elbow connected to the suction flange wouldn't meet the intent of 4.16.3.3.

Jack G

8/24/2024 09:23:38 am

If the supply is from above, 10 diameters is code.
The eccentric is used for the pump flange (different than supply flange).
Mechanically speaking and per pump design books, the flat part is on the bottom as the elbow reversed the air pocket.

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Vertical Reducer in Before Vertical Inline Pump?

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