dry system delivery time

[coarts]

Does anyone know the best way to get an inexpensive [or free] program that would estimate the water delivery time for a dry system. We have hydratec calc that may be used somehow to input the info. Thanks for any suggestion.

 

[TravisMack]

The only program I am aware of that will do it is the Tyco FDT program. Last I recall, it is about $5k. Hydratec will not be able to do it with the current version. I am not sure about future versions.

FDT calcs are a pain to input unless you have a tree system that is typical for everything.

Also, it is supposed to work on "simple" loops, but not compound. I put in a large preaction system that was a "simple" loop. After many problems, I sent the file Tyco. They just said. "well, I guess it won't work on that loop."

It is a great program and was within 0.5 seconds of actual trip time. But, it is tedious to input based on what I saw at the time.

Travis Mack
MFP Design, LLC

 

[ContractorDave]

Well that's interesting. How DOES an FPE go about designing a dry system to satisfy the 60 second requirement (where it's called for)? And while we are here, what is the reason for not allowing check valves to be installed to subdivide a large system? I did an inspection in an arena where a curling rink had been added and the system extended to cover there. The time for water to reach the inspectors test was over 3 minutes. Installing a check valve would help alleviate this delay no? As long as drains were installed properly etc.?

Regards
Dave

 

[cdafd]

weren't the check valves allowed in the past???

 

[TravisMack]

Yes, you could use check valves to subdivide a system. I believe this option was removed in either the late 80's or early 90's.

Travis Mack
MFP Design, LLC

 

[SprinklerDesigner2]

"weren't the check valves allowed in the past??? "

Yes, but not now.

"Well that's interesting. How DOES an FPE go about designing a dry system to satisfy the 60 second requirement (where it's called for)?"

Gut instinct based on past experience with similar systems having similar water supplies.

When in doubt prepare to manifold the riser ahead of time.

Just finished with a system having a 1,060 gallon capacity but I wasn't to worried knowing I had 152 static, 150 residual flowing 2,080 gpm. FM job so it wasn't pressure that dictated pipe size but velocity which had to be < 25 fps. This system delivered water to the inspectors test in 55 seconds.

But I wasn't sure so when I laid the system out I made it so if I had to divide the system all I would have to do would be to add a second dry valve and few joints of 6" galvanized pipe. I was unsure enough I left a tee with a blind flange below the shut off valve.

Would have cost me around $3,500 if I absolutely had to and while it would have made me cry it wouldn't have been an unmitigated disaster.

There is a formula to calculate time to trip the valve but I lost it. Anyone have it?

 

[chevy4x4trucks]

Another option to look into is the Victaulic NXT dry pipe valve. It requires a lower air pressure so you get a faster delivery time. We have installed some systems over 1,500 gallons and still were able to deliver water in under 60 seconds.

Otherwise unless you want to buy Tyco's software you are safer just keeping your systems smaller.

 

[ContractorDave]

I agree with Chevy there, the 768 is a superior product, especially since you can buy it prefabbed to the nines. I like the DV-1 for it's simplicity, but performance wise it doesn't hold a candle to the Victaulic valve. Any one else have another preference?

Dave

 

[Bagge]

"It requires a lower air pressure so you get a faster delivery time."

I have aways thought that you would get a faster delivery time if you had a high air pressure rather than a low in the system. The argument for this should be that you would have a more compressed system, which should result in a faster delivery time - but am I totally wrong here?

 

[ContractorDave]

Due to "air" being compressible, the more pressure you have in a 'system' the greater the volume of air that has to be released before a system can operate. Maybe to make it more clear: if I have a 100 gallon cylinder with a 100 gallons of water at 0 psi, I still have pretty much the same volume of water at 100 psi. Air has a compressibility factor; where a 100 gallon cylinder with air in it at 100psi has more air in it than when the same cylinder is at atmospheric pressures (depending on temperatures and whether we are speaking a nitrogen atmosphere or "air", etc..). In a dry sprinkler system then, greater air pressures equate to longer trip times which is of course undesirable. This is one of those things that at first blush may appear un-intuitive, and I've often found dry systems where air pressures have been cranked up to compensate for small leaks or the odd pressure spike. Not good


Regards
Dave

 

[Bagge]

Thank you for a fast reply, Dave.
I'm aware that it will take longer for the valve to operate if you have a high air presure - if you haven't got a accelerator that is. In this case it will be the 'water transit time' that will be the decisive factor. And it is here that I see the benefit by the high air presure. Or?

 

[ContractorDave]

My apologies Bagge, I'm not quite understanding your point of view. The higher the initial air pressure in respect to a given water supply pressure on a differential dry pipe valve, the longer it will take for the air pressure to reach the differential trip point that will allow water to release into the system. The dynamics of what will happen in a system where you have an accelerator or a dry pipe valve like the 768 with high air pressures would probably be difficult to model, but I'm assuming that the air will NOT be conducive to better operation of the sprinkler system / spray / discharge patterns, and is not accounted for in testing for listing approvals.

Regards
Dave

 

[desnov74]

I had a similar question in post

http://www.eng-tips.com/viewthread.cfm?qid=212854&page=2

The folks in Tyco refered me to somebody who did this type of work on a job basis, so they could supply you with the calcs for a fee.

I dont recall his price.

 

[ContractorDave]

But Travis had the most accurate answer in regards to your question as it relates to this thread: the TYCO FDT is THE software to go with to figure out "the time it will take water to get to the inspectors test". I am sure there is an old school pencil and paper way to figure it out but there's obviously a ton of variables. It may be interesting to try it once.....

Regards
Dave