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The new-construction townhouse has a fire-suppression/sprinkler system installed, and the water pressure is 110 psi (as shown by the installed gauge on the suppression system). I recommended a pressure-reducing valve be installed on the house side of the water meter (but beyond/after the sprinkler system "T"); the townhouse appears to have the same 110 psi pressure, and I worry such can promote plumbing component damage.

I've found a couple internet thingys that say 80 psi is maximum recommended pressure for a domestic water supply, but nothing I found can be construed as written in concrete. Any thoughts on this, or any source one might know of to point the builder to?

In the attached picture, the fire-suppression is on the left side of the water meter, and I recommended the reducing valve be installed on the right side of the meter. . .

(Or, can some type of water meter act/serve as a pressure-reducing valve?)

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tn_201411913335_Sprinkler.jpg

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I think you're right about 80 psi being the maximum for the SPPC (silver-painted-plastic-crap) we frequently see, but I don't have any concrete language for you. I would punt to a plumber for further evaluation if I came across 110 psi in any house, with or without a sprinkler system.

Where is the service entrance?
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I think you're right about 80 psi being the maximum for the SPPC (silver-painted-plastic-crap) we frequently see, but I don't have any concrete language for you. I would punt to a plumber for further evaluation if I came across 110 psi in any house, with or without a sprinkler system.

Where is the service entrance?

In the picture, immediately left of the water meter, through the back foundation wall (where if you look close, you can see the handle on the ball-valve water main is turned slightly off). It "T's" to the left to the sprinkler system, to the right to the domestic.

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Did you put a pressure gauge anywhere on the "house" side?

I suspect the fire suppression piping system is pressurized to 110, but the backflow device does not allow that pressure to transfer into the house piping.

No. Went through four pressure gauges the first five years of biz, then quit using them. This is one case where I wish I still had one.

What backflow device, Bill?

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What backflow device, Bill?

The backflow device in your pic is a double check valve assembly (under the hanging instruction sheet) that has 4 test cocks sticking out the right side.

Okay, thanks. But the location of the check valve doesn't seem like it would reduce pressure to the right of the water meter. The main water supply inlet is almost directly in-between the meter and the check valve (supply is coming out of the white-insulated foundation wall).

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Did you put a pressure gauge anywhere on the "house" side?

I suspect the fire suppression piping system is pressurized to 110, but the backflow device does not allow that pressure to transfer into the house piping.

Exactly as Bill said.

I've had this same thing on new home inspections. Checked the exterior hose bib and got 60psi. The county inspectors want to see the sprinkler system pressurized to a certain point. The check valve holds it in while on the house side the pressure is lower.

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Did you put a pressure gauge anywhere on the "house" side?

I suspect the fire suppression piping system is pressurized to 110, but the backflow device does not allow that pressure to transfer into the house piping.

Exactly as Bill said.

I've had this same thing on new home inspections. Checked the exterior hose bib and got 60psi. The county inspectors want to see the sprinkler system pressurized to a certain point. The check valve holds it in while on the house side the pressure is lower.

That makes sense, but I can't wrap my head around why. If the pressure at the street is 60 psi or there abouts, wouldn't the fire suppression system flow at 60 psi after a short burst of high pressure? (I'm surely missing something here.)

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Did you put a pressure gauge anywhere on the "house" side?

I suspect the fire suppression piping system is pressurized to 110, but the backflow device does not allow that pressure to transfer into the house piping.

Exactly as Bill said.

I've had this same thing on new home inspections. Checked the exterior hose bib and got 60psi. The county inspectors want to see the sprinkler system pressurized to a certain point. The check valve holds it in while on the house side the pressure is lower.

That makes sense, but I can't wrap my head around why. If the pressure at the street is 60 psi or there abouts, wouldn't the fire suppression system flow at 60 psi after a short burst of high pressure? (I'm surely missing something here.)

I'm not totally sure but the initial charge you see may be residual from system testing when it was installed. In order to measure a specific flow capability higher up in the structure they have to charge it up high.

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Never thought about this. With a sealed system and no expansion tank I suppose the pressure in the sprinkler system could increase due to in hot weather, but the pressure should come back down when the water cools. But, many systems I have seen have a relatively high pressure in the sprinkler system piping and have a PRV in the domestic piping.

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Did you put a pressure gauge anywhere on the "house" side?

I suspect the fire suppression piping system is pressurized to 110, but the backflow device does not allow that pressure to transfer into the house piping.

Exactly as Bill said.

I've had this same thing on new home inspections. Checked the exterior hose bib and got 60psi. The county inspectors want to see the sprinkler system pressurized to a certain point. The check valve holds it in while on the house side the pressure is lower.

That makes sense, but I can't wrap my head around why. If the pressure at the street is 60 psi or there abouts, wouldn't the fire suppression system flow at 60 psi after a short burst of high pressure? (I'm surely missing something here.)

Any further help with this would be appreciated.

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Some insight on residential fire sprinklers.

When the system is inspected in the combo phase by the AHJ, a pump is connected to the inspectors test valve to back fill and pressurize the system up to two and a half times the system pressure to check for leaks. At final, the system is flowed to check the flow switch and alarm. If the city supply is less then what shows on the sprinkler system gauge, the added pressure is most probably from building or attic heat.

In colder climates the pipes for the sprinkler system could be charged with an anti-freeze mixture. The mixture should be checked for proper concentration annually.

Some sprinkler flow alarms are interconnected with the smoke detectors and will set off all the smoke alarms.

The water provider should require the back flow prevention valve to be certified (tested) each year.

The inspection points that an HI should observe would be;

The valves that control the the sprinkler system are open.

That there are no leaking sprinkler heads.

The branch circuit that powers the flow alarm is on.

I would recommend that a Fire Sprinkler Co. do an annual inspection and that the Back Flow valve be certified.

Lee

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