Dry pipe system capacity 1,409 gallons... yeah.

SprinklerDesigner2 · Nov 8, 2013

Yesterday I trip tested a newly installed dry pipe system having a capacity of 1,409 gallons using city water only (no fire pump) with results as follows:

Static Pressure 61 psi
Residual Pressure 58 psi
Pitot Pressure: 35 psi (2 1/2" Hydrant Butt)
Rate of Flow 993 gpm

Flat roofed building with sprinklers 25' above the static/residual fire hydrant.

I've successfully trip tested some 1,250 gallon capacity systems but they always had a large fire pump with with a lot of kick behind it. Never something this big. What I had was a 6" valve on 6" riser manifold fed from 10" city water main through 100' of 6" underground which included a 6" meter and 6" Ames 2000ss double check.

System had a capacity of 1,409 gallons (yeah, it was really that big) having 100' of 6" feed main with two 4" mains and 2" branch lines on tree system.

I wasn't completely nuts because when we laid out the system I did it in such a way we could have easily manifolded the riser making two systems of less than 750 gallons involving a days extra labor and the cost of a dry valve with trim. When I laid the system out I did so anticipating failure. I even went so far as to warn the AHJ that I was experimenting, the reasons why I was experimenting and being the understanding sort he was as curious as I was to see if it would work. If I did fail at least I wouldn't have all kinds of egg on my face.

When I bid the job I had the price for a manifold riser so it wasn't like the additional cost of failure would be overly high.

Here is what I got.

Time to trip was nearly instant and I think I got maybe 1 1/2 seconds. Total time to water to reach the inspectors test (1/2" SBO) was 0 minutes and 58 seconds.

Here is what helped me and might someday help some of you.

A few months ago I got bored and for some easy late night reading I spent a few hours going over paper by James Golinveaux, Sr. Vice President, Research & Development Tyco Fire & Building Products

For my fellow technicians out there this is very much a worthwhile read!

A Technical Analysis: Variables That Affect The Performance Of Dry Pipe Systems

If you haven't seen it it's good stuff throughout but especially starting on page 14.

For the dry valve I used the Reliable 6" DDX-LP Dry Pipe Valve System with accelerator which required only 15 psi of air.

Trip time was nearly instant, less than two seconds on my stop watch, with a steady stream of water delivered to the inspectors test in 0 minutes and 58 seconds. All this through a half inch orifice to boot!

Word of advice, on a system this big I would always leave myself some sort of easy out in the event of failure.

If you do the kind of work I do read that analysis because it is well worth your time... to help I also did a little trick with a 1" "loop" on the last two branch lines to allow air to compress in the closer non flowing main instead of being forced out of the inspectors test. I think it worked.

Best part of all this? The fitters were all betting me beer it wouldn't work and I won. You should have seen their faces. [pipe]

LCREP · Nov 8, 2013

Will you get 58 seconds in 5 years from now when the pipe is nice and rusted? That is the bet I would like to take.....lol.

Thanks for the link to the paper, James is one heck of a nice guy and extremely knowledgable. I was at a recent NFPA seminar in Chicago where he said in public, here is my cell number call me if you have any questions.

Thanks for the info, glad it all worked out. What was the design of the sprinkler system?

SprinklerDesigner2 · Nov 9, 2013

Building is used for cold storage of food but not frozen.

Temperature is kept between 42 and 50 degrees and while a wet system would be ok it's the owner who wants a dry system.

System was designed to a density of .15/2,600 W/500 Hose. In accordance with state fire marshal rules I maintained a 10 psi safety factor (actual was 11.5 psi).

No rack storage, all solid pile.

General layout was similar to what I show below:

What's that "single piece of 1" pipe creating a 'loop' doing? Maybe I didn't interpret the paper right but one of the things I picked up was I wanted the air in the left side main to have a place to compress so my hope was some of the air would compress in the right side of the loop instead of more of it having to be discharged through the inspectors test connection. One of the things I got out of it was this allow the air pressure to remain at somewhat lower on the left side main allowing that main to fill more rapidly at least that was what I was thinking.

Hydraulically the 1" doesn't make any impact so if it wouldn't have worked I could have split the system up by simply adding a new riser on the manifold (I already had the outlet for it which gives an idea how sure I was that it would work) , removing the 1" giving the system on the left a capacity of just under 750 gallons. By under it would have been 746 gallons in which case I would not have had to meet the 60 seconds.

Then there is the inspectors test using a 1" globe valve even though the drawings indicated the use a full port ball valve. I think I could have knocked another couple seconds off the time.

About the advantage of the "loop", did I interpret the concept of what the white paper was saying correctly? The paper referenced a reservoir to hold the air which was basically what we did with main in the east side of the system.

I wanted to experiment doing a second trip with the 1" removed but the moment the fire marshal said they could move in the fork lift trucks were moving in stock.

Also, not mentioned until now I had a second system #2 which was a single straight tree system having 751 gallon capacity and no 1" loop trick. On this system water was delivered to the inspectors test in 0 minutes and 42 seconds.

LCREP · Nov 9, 2013

Too bad he went with a dry pipe sprinkler system he will pay more $$$ in insurance premium for the life of the building. Most insurance companies charge more because of the lower reliability of a dry pipe valves.

But I like your design.

stookeyfpe · Nov 9, 2013

SD2:

I'm seeing the smart designers using the Reliable or Victaulic differential pressure DPVs and subdividing larger systems.

One observation from about 15 trip tests over the past year is the installing technicians are not being educated on the low and high air pressure limits. I've inspected several jobs where the riser has 30-40 PSIG of air because that's the way do it. Both Reliable and Victaulic have very low charging pressures (can be low as 13 PSIG and never above 24 PSIG). This information is clearly defined in the manufacturer data sheets. One other interesting factoid is that Victaulic requires the installation of a QOD if one chooses to exceed the upper air pressure limit, and of course it needs to be listed as compatible with Victaulic components. That alone convinces everyone to read the installation instructions.

SprinklerDesigner2 · Nov 9, 2013

Stookey,

The manufacturers literature was very clear that when using an accelerator the minimum air pressure is 15 psi which is right where I had the guys put it.

With such low pressures we can use smaller air compressors as well.

I still can't believe we got the time down to 58 seconds. Reliable has a slide titled "60 second success stories" where they reported trip times on a variety of systems having different water supplies but but nothing nearly as big as my system having the water supply it did. Based on what the manufacturer supplied I had doubts but fell back on the "loop" idea in Tyco's white paper. I am still shocked it did so well and that I can only attribute to the "loop trick" for lack of a better term.

Normally we put up a tree and the cross main might end six to twelve inches beyond the last branch line riser nipple feeding the line having the inspectors test. But what if we extended that main, say it was a 4" cross main and we increased it to 8" extending one or two full joints beyond the last branch line giving the air a place to compress instead of having more of it discharged through the inspectors test?

Flies in the face of everything we ever learned but we all have of examples where we simply accepted the wisdom we were told only to find out later it was wrong and never based on anything. Like sidewall sprinkler positioning or sprinklers up in pockets vs sprinklers positioned at the bottom of beams. Wisdom passed down from 100 years ago based solely on what someone long dead once thought.

LCREP · Nov 9, 2013

Please do me a favor and put a sign on the valve that says the following:

Air pressure MUST be set at 15 psi as per manufactures and designers requirements.

This will be for the next so called experienced contractor changing the psi because it was too low since they always set them at 40 psi! I hear this every time I teach contractors that have been told you do it this way because they have always done it this way. The paper work that came with the equipment you never read since they are for novices that do not know what they are doing. When you think of all the new valves that have come out in the last view years, you can not use seat of the pants I have always done it this way thinking.

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Dry pipe system capacity 1,409 gallons... yeah.

SprinklerDesigner2

Mechanical

Recommended for you

LCREP

Specifier/Regulator

SprinklerDesigner2

Mechanical

LCREP

Specifier/Regulator

stookeyfpe

Specifier/Regulator

SprinklerDesigner2

Mechanical

LCREP

Specifier/Regulator

Similar threads

Part and Inventory Search

Sponsor