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Backflow preventers again

Backflow preventers again

Backflow preventers again

(OP)
For inspections of buildings with backflow devices I'm assuming NFPA25 12.6.2.1.3 applies. What then would the intention be in flowing say the existing main drain... Are we just doing a typical main drain test and this will reflect a forward flow test of the backflow preventer also?
Also, in reading some of the posts I am leaning to the conclusion that a fire pump downstream of the DCVA makes the forward flow test un-necessary?

RE: Backflow preventers again

(OP)
Sorry. In reading 12.6.2.1.3 my nose was too close to the book and I missed the next paragraph (.4). I am still puzzled though.... in doing a flow test it seems I may use a loop with a site glass to verify a flow. How does this tell me if system demand is being met?

RE: Backflow preventers again

"Also, in reading some of the posts I am leaning to the conclusion that a fire pump downstream of the DCVA makes the forward flow test un-necessary?"

This is correct.

A pump test requires 150% of rated capacity and you can not design a system that exceeds 150% rated capacity of the fire pump.

I would guess a 2" main drain would be fine on a lot of light hazard systems.  Not all but a lot of them especially if the designer used the quick response/low ceiling reduction for the ara of application.

On Ordinary Hazard Occupancies *some* might be OK with a 2" main drain but I would guess most city water supply systems would fail to deliver the required flow. For ordinary hazard occupancies it wouldn't be that big of a deal to reverse the fire department check valve and use the 4" FDC to achieve the flow.

On most high piled storage/extra hazard occupancy systems the 4" might not be able to deliver the required water supply and I can see something similar to a fire pump test header or a straight pipe larger then 6" discharging outside the building.

On larger systems you might find a fire hydrant downstream the fire pump and you can always use that.

I suppose you can always run a 4" or 6" main drain too.  Not a huge deal just a butterfly valve, little bit of pipe and couple elbows.

In Georgia I have yet to be anywhere this is pushed.  In South Carolina an actual pump test header assembly is required.

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