Dry system loop

[KINGSPRINKLER]

Is it acceptable to loop a dry system? I know you can't grid one, but a loop?

 

[LCREP]

Yes, BUT you may find it difficult to meet the trip times depending on the size of the system, density and design area, etc. If u are in NJ minimum trip time is 1 min regardless of the occupancy.

 

[TravisMack]

King:

You can loop, or even compound loop a dry system. You are limited in that you can't grid it. If you keep your volumes under 750 gallons and NFPA 13 is your only standard to comply with, then you don't need to meet the 60 second trip time.

The FDT calc programs do not calculate loops. They are only UL Listed for tree systems.

Good luck!

 

[SprinklerDesigner2]

I will add my yes that you can loop dry systems.

http://findarticles.com/p/articles/mi_qa3737/is_200403/ai_n9381198

If designers had used some common sense we'd still be allowed to grid small dry systems too.

 

[sfallows]

the new code nfpa 13 2007 required both calc and field testing, previous nfpa codes allow for one or the other.

The calc program for trip time can be quite costly.


Check the communities building code see what year it refrences.

additionally the increase of 30% for dry systems will increase the pipe sizes and then increase the volume


I recently designed a large loop system in a northern suburb of chicago the town required both field test and calculations. With no exhauster or accelerator the calculation (flowing multiple heads) had water at the head in 14 sec. but the field test with nfpa 2006 inspectors test connection (before the changes that occurred in 2007) it took 2.5 min.

 

[FFP1]

I agree with all of the above comments except for the "common sense" reference by SprinklerDesigner2.

Grid designs are not allowed; looped systems are allowed (with supporting tests or calculations as mentioned above), however, I do not think it is a good idea to use gridded or looped designs for dry systems. In my opinion, NFPA 13 should be altered so that grided and looped systems are not allowed for dry systems. Except for very small systems, the actual trip test times will exceed the maximum trip time required by code. The computer calculations are usually incorrect as Tindey's example suggests. The required trip time (for constant water flow at the most remote point) varies depending on several factors. Refer to Section 7.2.3.6 of NFPA 13 for specific details.

Gridded dry pipe systems are worse than looped dry pipe systems, but both cause problems and lesson the likelihood of a controlled fire.

The problem should be obvious to anyone who has conducted numerous trip tests on these systems and/or or anyone who has a really good understanding of hydraulics. The air pockets constantly shift due to "balancing" of the system pressure in various portions of the grid and/or loop. During trip tests, the water is delayed and then the inspector's test connection has intermittent discharge of water then air then water then air......

This is not a good scenario during a real life fire incident!

But we can save $$$$$ on our material costs and add a little profit for our company..........is it really worth the increased liability and risk? What are the increased costs if a truly qualified inspector conducts a trip test and the system requires 3.5 minutes before CONSTANT water flow reaches the most remote point of the system?? Accelerators and exhausters will not always reduce the trip time enough to mask the real problem (caused by the shifting air pockets). Just use a tree design for dry pipe systems.......I assume most Fire Protection PE's would agree.

 

[KINGSPRINKLER]

Thanks to all,
I'm always adding to my knowledge of this ever expanding field. We don't do many dry systems here in northern California.