Backflow preventers again 1

[ContractorDave]

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?

 

[ContractorDave]

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?

 

[SprinklerDesigner2]

"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.