Sprinkler systems with high municipal water pressure

[bmlxd40]

I have a project where the municipal water pressure had a peak pressure of 169 psi when we did a 24 hour test. The building has an existing system, but no pressure relief valves, and thermal expansion has been raising pressures to as high as 250 psi on some of the systems. Obviously I will be installing relief valves on each system, but I am concerned about the relief valves operating the flow switch. Most pressure relief valves don't open or close at exactly the 175 psi limit, and I want to prevent an alarm if the relief valve doesn't shut of until ~165 or some such. Also, with pressures that high, there is a distinct possibility of the municipal water surging above 175 from time to time.

Does anyone have any ideas? The owner wants to eliminate all possibility of false alarms.

 

[cdafd]

not a designer or engineer


one story building??

can you put one on the riser prior to the wter flow switch?? and then down stream?

http://www.cla-val.com/documents/pdf/CV_Fire_Products_Catalog.pdf

check page 54 and 56


is the hyrdaulic calcs available to see what is needed?

 

[Lamuppet]

Put a retarding chamber.

 

[AZsprink]

I agree with CDAFD. Does project have backflow preventer? Can you install a pressure regulator, and recalc. Was original system installed with extra heavy pattern piping, and heads? I would worry about the listing of materials. Most are 175 PSI max working pressure. Maybe you could talk to Municipal water dept etc. to see if maybe there is a problem with regulation etc.

 

[Sdpaddler50]

A backflow preventer is not going to prevent these surge pressures from coming in to the system piping.

Thermal heating of the water in the pipe during the summer is probably one of the causes. This is an issue that is tough to deal with when you are already at 175. I have also seen pressures above the check valve on the riser climb up, and i agree 250 is pushing it. My experience is those little PRV (1/2 in for example) are not that great and end up loosing their calibration after a few years.

Unfortunately i dont have any other solutions to offer you, but i am curious to hear what others (sprinkler contractors out there?) have to say on this subject.

 

[bmlxd40]

Thanks for all the help, folks. The first thing that came to our mind was Cla-Val. The system currently has pressure switches on retard chambers in leiu of vane type flow switches. However, there are currently no relief valves installed, so in the current configuration, the chances of the alarm valve opening are slim to none, once the thermal expansion takes place. Since the owner wants to guarantee as much as possible, that there wont be any false alarms, a Cla-Val may end up being the best option. The hydraulic placards on the risers aren't readable, so we will have to see what the calcs come up with.

 

[DavidCR]

If preventing false alarmsis the objetive, I´d prefer a vane type flow switch that include an adjustable retard of 30s (default, adjustable from 10-90s generally) designed to prevent false alarms.

 

[stevenal]

The electrical solution is to have a second contact supervise the first. Put a second flow switch with a NC contact on the pressure relief vent. Wire the two contacts in series to actuate the alarm.

 

[MGXFP]

Have you bled all the air from the system? That will help greatly to reduce the temperature related pressure surges. I think most flow switches require 4-10 GPM to sound an alarm. I don't know if a relief valve will flow that much.