nfpa 8.16.4.6.1 2002 edtion

[cdafd]

Anyone enforcing this and if so what is the piping set up??
What actual gpm flow are you requireing???


8.16.4.6.1* Backflow Prevention Valves. Means shall be provided downstream of all backflow prevention valves for flow tests at system demand.


A.8.16.4.6.1 The full flow test of the backflow prevention valve can be performed with a test header or other connection downstream of the valve. A bypass around the check valve in the fire department connector line with a control valve in the normally closed position can be an acceptable arrangement. When flow to a visible drain cannot be accomplished, closed loop flow can be acceptable if a flow meter or site glass is incorporated into the system to ensure flow. When a backflow prevention device is retroactively installed on a pipe schedule system, the revised hydraulic calculation still follows the pipe schedule method of 11.2.2 with the inclusion of friction loss for the device.

 

[sprinklerdesigner]

It's spotty at best but more AHJ's are catching on that it is a requirement.

You will find this inforced in many areas of South Carolina but not all.

System demand would be the demand developed in the hydraulic calculations for the particular occupancy and, depending on the occupancy, it may even be possible to accomplish the full flow test using a main drain.

For an Ordinary Hazard Group II occupancy the theoretical fire flow is going to be somewhere around .20*1500=300 gpm + 10%) or somewhere around 330 gpm. As noted on the appendix in most cases this flow should be easily obtained by simply installing a valved bypass around the fire departement connection.

For many 13R residential systems it is possible to meet the flow requirements, in worst case most of the time this is only arund 70 to 90 gpm, through the a 2" main drain if using a full port valve in lieu of a globe valve usually found.

If the system has a booster pump installed downstream the backflow preventor the problem is mute solved by the pump test header.

Where I can see a problem is systems developing a high demand rate using only the city water supply as in an Extra Hazard Group II Occupancy. With some public water supplies it may not be possible to achieve a system demand flow through a typical 4"x2 1/2"x2 1/2" fire department connection.

 

[LCREP]

I work for an insurance company in New Jersey and require the testing outlet. Many contractors are not aware of the requirement and usually say no one has ever asked for the connection, I then point them to the section in NFPA 13. 150-400 gpm is about what you would expect from a main drain test flow. Once you get past Ord Grp 2 occupancy I require a test header or by pass around the check valve on the FDC. It is great to put the connection in place another thing is to get the contractor to perform the annual forward flow test on the device. Many completely miss this requirement in NFPA 25.

 

[sprinklerdesigner]

LCREP,

I was thinking this morning of rigging up a 1 1/4" playpipe tip with 45 deg elbow and 2" nipples to give to our inspection department so they might conduct "flow test" of different systems during regular inspections.

It would be interesting to determine what the actual K-Factor's for different main drain arrangements turn out to be.

I've got an old factory mutual book around here, published in the early 1950's but contains loads of informational tidbits you can't find anywhere else, that gives K-Factors for different main drains and I will have to see if I can find it.

I am thinking most systems above an Ordinary Hazard Group II occupancy would require something more then simply two outlets provided by a bypass around the fire department connection. Take a system designed for a density of .60/2,000 you are looking at a theoretical minimum system demand of 1,200 gpm and will probably end up around 1,300 gpm or more. I doubt many city water supplies don't have the kind of pressures needed to expell 1,300 gpm from a 4" bypass around a fire department connection.

If something like this was up to me I think I would use a four hose outlet pump test header connection fed with 6" pipe directly from the riser. Wouldn't be all that expensive a couple grooved elbows, a maybe just a plain end pipe outlet?

Probably work if you used 4" pipe directly from the riser with a 4" 45 deg. turned down grooved elbow similar to a main drain setup.

 

[LCREP]

Sprinklerdesigner

At our Training Center we attached an ulrasonic flow meter on the 6 inch line feeding the riser and varied the pressure with a fire pump on and off and by turning valves down. The high and lows were about 150-400 gpm with residual pressure from 60 psi to 150 psi. The typical globe main drain valve does not open 100% and has a lot of friction loss.

As part of the final sign off we will witness the flow test on the back flow to insure we have enough flow to meet the largest flow for the system. If the bypass around the FDC does not work, then a pump test header usually works! Contractors are not happy when we ask for the test to verity the flow, but we are the ones that pay the claim!

In northern NJ we do have some areas with excellent water supplies with static pressures of 100-150 psi and residual pressures in the 90-140 psi range, enough not to need a fire pump on some ESFR systems. In fact at our training center we have a static pressure of 175 psi! We have it reduced down to 150 psi, and sometimes that is too much!

 

[sprinklerdesigner]

Let's see if this works.

K=150/(60^.5)
K=19.37
Q=19.37*(150^.5)
Q=237

I was afraid of that, unrealiable based on your readings but then with the angle valve it doesn't really surprise me. On a 2" angle valve the orifice opening on the seat is less then 1" from what I remember.

Change the angle/globe valve to full port ball valve and I think you will be surprised at the difference and as an added plus you might find K-Factoring more reliable.

Around here our static is 55 to 65 regardless of where you are.