Preaction system - air pressure vs water pressure?

[Bagge]

Hi,
I'm planning to use a 'Single Interlock Preaction Type A Sprinkler System (Tyco Model DV-5)' in a project. The system is electrically activated.
Regarding this I have a maybe little silly question - but I hope you can bear with this.
The electrical system activates which will activate the solenoid valve and fill the system with water. The system has an air pressure of 10 psi. The electrically system will activate before the sprinklers which brings me to my question; will the air pressure disappear from the pipe system when the water will fill the system -and where to? I can not see that there is a valve for this purpose? Or is it such a small air pressure, that it is a theoretical issue rather than practical?

I hope a kind soul will find the time to an answer - thanks in advance!

 

[LCREP]

The air gets compressed at the end of the pipe and or comes out of the sprinkler when it activates.

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[pipesnpumps]

Are you familiar with ideal gas law? If 10 psig air is compressed by 40 psig static pressure water, then it will occupy 45% of it's original volume. (14.7+10)/(14.7+40) = 0.45.

I had the same questions you did. I still haven't figured if air is actually required.. It wasn't clear that it is, and NFPA 13 seemed to conflict itself but it is standard practice to use low pressure compressed air.

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[skdesigner]

NFPA 13 2010

7.3.2.4.1 Sprinkler piping and fire protection devices shall be automatically supervised where more than 20 sprinklers are on the system.

7.3.2.4.4 All preaction system types described in 7.3..2.1(2) and 7.3.2.1(3) shall maintain a supervising air or nitrogen pressure of 7 psi.

Low air switch will kick the panel into supervisory mode when you lose the air pressure. Deluge valve on a single interlock doesn't go until it gets a signal from a detector (electronic actuation). So, you could have a great big hole somewhere in the system and not know until it was too late.

 

[pipesnpumps]

Ah, But 7 psi is not required for the typical preaction system, a single interlock 7.3.2.1(1). Right?

(2) is noninterlock, (3) is double interlock. The 7.3.2.3.2 reqt for 7 psi air doesn't apply to single interlock.

And yet 7.3.2.3.1 still requires piping to be supervised. The only logical way to supervise the piping is with.. Compressed air. So the net effect is you still need compressed air, just not at any certain pressure...


This was also curious to me, from definitions. I'll quote 2002 version which I have handy at home: definition of preaction system,
3.4.8 "a sprinkler system.. attached to a piping system that contains air that might or might not be under pressure, with a supplemental detection system installed in the same area as the sprinklers"

Um, just how can you supervise the piping if the air is not compressed???

What I might or might not understand is why anyone would put one in with out air and not have a decent supervisory pressure. It also would depend on the water to pressurize the system prior to the sprinkler head fusing.. A sprinkler needs 7 psi to eject cap properly so it is ready to sprinkle, or it can get caught and disrupt spray pattern.. Detectors should actuate well before the sprinkler in theory, early enough to pressurize but I wonder on very large volume systems..

Just seems odd that NFPA 13 doesn't require 7 psi air for single interlocks too...

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[cdafd]

 A sprinkler needs 7 psi to eject cap properly so it is ready to sprinkle"""

What cap??????

 

[pipesnpumps]

Huh??? You know, the cap, the valve cap, the mechanism, the part that goes in the orifice and holds the water back.

http://en.wikipedia.org/wiki/Fire_sprinkler

Calls is a pip cap.
NFPA calls it a cap.. What should I be calling it then?


Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[cdafd]

Oh learn something everyday!!!!!!!


Now I can impress my boss