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Sprinkler water main gage and back flow preventor

C

cda

SAWHORSE
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Oct 19, 2009
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If you have a back flow preventor as part of the sprinkler riser stack.

Where should the gage be for the city water main pressure coming into the system??

Before the back flow preventor??

or

After the back flow preventor?
 
If you have a back flow preventor as part of the sprinkler riser stack
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What do you mean "If"?

Backflow preventers are required on all automatic fire suppression systems connected to a potable water system.

IPC

608.16.4 Connections to automatic fire sprinkler systems and standpipe systems.

The potable water supply to automatic fire sprinkler and standpipe systems shall be protected against backflow by a double check backflow prevention assembly, a double check fire protection backflow prevention assembly or a reduced pressure principle fire protection backflow prevention assembly.

Exceptions:

1. Where systems are installed as a portion of the water distribution system in accordance with the requirements of this code and are not provided with a fire department connection, isolation of the water supply system shall not be required.

2. Isolation of the water distribution system is not required for deluge, preaction or dry pipe systems.
 
In the thousands that I have worked with, the water pressure gauges are typically on the discharge side of the backflow and located on the supply and discharge sides of the alarm/check valve. The manufacturer's cut sheet will tell you how many pounds of Friction Loss you have with the backflow or RPZ assembly (typically 8 to 10 pounds). You can also see them on the supply and discharge sides of the backflow or RPZ.
 
Reason for the question

If you put the gauge meant to tell you what the city water main pressure is after or above the back flow preventor

Is that actually showing you the city water main pressure or the trapped pressure in the system ????
 
FM William Burns said:
The one on the supply side of the alarm/check valve will show you the water system's static pressure +/- 10 psi for the backflow assembly. In this case it looks like an AMES Colt Series. So you would have about 9 psi loss according to Page 2:http://media.wattswater.com/ES-A-C300-C300N.pdf
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To me if you put the gauge for the city water main pressure on top of the backflow in the picture,

The pressure above the top of the backflow is trapped pressure and not a true indication of the city water main pressure.

If all you had was the backflow and no other check or alarm valve above it as in a shotgun riser, the gauge would be reading the system pressure. Which would fluctuate with the temp
 
I'm a bit confused. There should be an alarm check valve to make notification of water flow. NFPA 13 requires a pressure gauge above and below the alarm/check valve [7.1.1.2]. With regards to a "shotgun" riser, there should be alarm/check valves on each riser extending vertical from the horizontal supply.
 
FM William Burns said:
I'm a bit confused. There should be an alarm check valve to make notification of water flow. NFPA 13 requires a pressure gauge above and below the alarm/check valve [7.1.1.2]. With regards to a "shotgun" riser, there should be alarm/check valves on each riser extending vertical from the horizontal supply.
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The backflow meets the second part of your answer

8.16.1.1.3.2. 2010 edition

Than on a wet system just a regular flow switch to an alarm system or electric bell is good

No an alarm valve is not always required
 
""""""A shotgun riser eliminates the need for an alarm check valve because the backflow prevention device stops water in the sprinkler pipe from flowing back into the potable supply, and the electric switch provides a water flow alarm.""""""

My point is the backflow traps the pressure and you do not get the true city pressure with only one gauge """"after"""" the backflow
 
true, but the back flow prevent or will indicate water pressure that is supplied from the city and the newer NFPA 13 requires pressure relievers to reduce the surge pressure.... If you do a short drain test with the gauge prior the preventors, are you getting a true water pressure reading when operating the main drains? I think not, the pressure would be higher since the pressure drops in preventors..... thus to get an accurate main drain test it would have to be after the preventors...
 
Builder Bob said:
true, but the back flow prevent or will indicate water pressure that is supplied from the city and the newer NFPA 13 requires pressure relievers to reduce the surge pressure.... If you do a short drain test with the gauge prior the preventors, are you getting a true water pressure reading when operating the main drains? I think not, the pressure would be higher since the pressure drops in preventors..... thus to get an accurate main drain test it would have to be after the preventors...
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That is one reason for the system side gauge

I keep wondering about the city water main pressure gauge
 
7.1 Wet Pipe Systems.

7.1.1 Pressure Gauges.

7.1.1.1 An approved pressure gauge conforming to 8.17.3 shall be installed in each system riser.

7.1.1.2 Pressure gauges shall be installed above and below each alarm check valve or system riser check valve where such devices are present.
 
Builder Bob said:
Sounds like only one pressure gauge is required...... if the back-flow preventor is outside the building, then the fire sprinkler system doesn't start until is 12" AFF..... (SHOTGUN RISER ONLY ---- Black Pipe - riser with flow switch...)
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Back flow in the building

And if outside you would more than likely have a shut off inside
 
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