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Active Member


Thursday, March 24th 2005, 4:23am

High water pressure

I got 72PSI and 12 GPM on a city watersupply. I'm afraid that I have to much water pressure, is it possilbe that I could have a water hammer problem when the values turn off to quickly? What can I do to keep my system from blowing apart?


Supreme Member


Thursday, March 24th 2005, 8:31am

From what I've learned at water hammer isn't about water pressure, it's about flow rate. If your pipes are sized large enough, you shouldn't have any issue with water hammer regardless of pressure.
You'd have to do the numbers, but a pressure of 72PSI sounds pretty good since you will lose some of that pressure as the water travels though things such as Back Flow Preventers. 72PSI sounds just right for using a RPZ Back Flow Preventer because you can expect a 12-15 PSI loss though it alone. I would hazzard a guess that if you do nothing about the pressure, but the time the water gets to the sprinkler heads, the pressure will only be about 40-50 PSI, and again, if the pipes are large enough (larger pipe = lower flow rate) then damage from water hammer should become a non-issue.


Supreme Member

Posts: 314

Location: USA


Saturday, March 26th 2005, 9:05am

In this situation, as noted by HooKooDooKu, pipe size is going to be key. For example, it would not be a wise decision to use 3/4" pipe for 72 PSI. Generally, on the systems we install on city water systems, we use at least 1 1/4" and sometimes even 1 1/2" pipe. All of the systems we install with pressures above 65-70 get a pressure reducer installed just after the connection to the main water supply. It may not need to be adjusted, but in case the water pressure ever increases or you do find a problem down the line with too much pressure, you will already have the pressure reducer there. They are not that expensive, and it is cheap insurance. Also, I might suggest that you use quality valves for your system. The cheap home improvement store valves snap closed a lot faster than the quality more expensive valves, and they are more likely to create water hammer.
Tony Posey
Ridge Run Landscapes

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