Backflow OS&Y Qualify as Pump Suction Valve?

5/24/2021

NFPA 20 Section 4.15.5.1 (2016 Edition) requires a listed OS&Y gate valve to be installed in the suction pipe, but the annex of NFPA 20 suggests it should be as far as practical from the pump suction.

Would a control valve (OS&Y) on the backflow preventer meet this control valve requirement of Section 4.15.5.1?

Assuming a city water supply, the backflow preventer control valve is listed for fire protection, there is still a valve'd bypass connected between the backflow preventer and pump suction, and the backflow is located a minimum of 10-pipe diameters from the suction flange.

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4 Comments

Glenn Berger

5/24/2021 08:39:39 am

The location of the bypass needs to be upstream of the suction gate valve. This will allow the use of the bypass while servicing the pump.

CJ Bonczyk

5/24/2021 09:48:11 am

OSY is still required to isolate pump for service, and allow city supply be connected upstream. This way, city supply still runs through BFP when the bypass is in use.

Casey Milhorn

5/24/2021 11:06:57 am

What Glenn and CJ said. But if you don't have a bypass I guess the backflow OS&Y could serve as that valve. On the other hand, if you don't have a bypass that probably means you have a tank only supply and don't need a backflow. Pretty rare to have a backflow without need for a bypass as well.

Franck

5/25/2021 03:47:30 am

As often, the answer will be "it depends"
It mainly depends on your fire pump arrangement on the suction side.

The purpose of the valve on the suction side (OS&Y, or gate valve, to avoid turbulent flow at the intake) is to isolate the pump for maintenance purpose/replacement, in particular if fed by a city water supply or a suction tank (gravity feed).
Note that in Europe, we still have horizontal fire pumps under lift (not allowed by NFPA since the 1970's) with a priming tank. In that case, you can disconnect the pump without issue from the suction side, and no gate valve is installed upstream the position of the pump (unless the higher water level is above the pump plan).

It is the same for the 2 valves (upstream/downstream) your backflow preventer : being able to make maintenance/replacement of your equipment.

To come back to your case, if you consider that you can isolate the fire pump on both side (suction / discharge) by using the valve from the backflow preventer without reliability issues, then you can consider that the valve from the backflow preventer is also your suction pump isolation valve.
Having a by-pass around the backflow is not an issue as you can also isolate the suction side with the valve on the by-pass.

But, as indicated in the introduction (it depends), maybe some configuration would require an additional sectional valve for your pump on the suction side (such as an AHJ decision?)

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Backflow OS&Y Qualify as Pump Suction Valve?

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