Water hammer and fire sprinkler system pressure reduce

[Qiyansun]

The attached shows my fire sprinkler system and the plumbing for the house. When I open the hose bib below or any faucet inside the house, the needle of the pressure gauge attached to the fire sprinkler system bounces and thundering noises from the ceiling. If I open the hose bib slowly, I don’t hear the noise and the pressure gauge needle moves from 65psi to 60psi gradually. Is this a water hammer inside the fire sprinkler system? Does the pressure change inside the fire sprinkler system indicates the check valve is bad?

 

[John Gayewski]

A single check valve isn't a backflow device. You need a proper back flow device to separate your sprinkler system and your drinking water.

As for a hammer arrestor you better get one or more of those also.

 

[Sponsor]

 

[Breplum]

I've plumbed many new homes in the last 10 years that had that exact setup.
I agree, that normally we see spec for RPP full-on backflow prevention even on irrigation...so how and why simple check got passed is a mystery, but, possible in some jurisdictions.

 

[Jeff H Young]

I've never seen a backflow on a house for fire sprinklers but seen many many check valves. A restaurant or apt complex a different story. Nothing unusual about no backflow valve on fire sprinkler system in single family homes in So Ca. but code could have changed but thousands upon thousands built this way after year 2000 and possibly till now.
My area has RPP on every home with irrigation sprinklers rather than just antisiphon sprinkler valves I don't know why but they aren't buying those backflow devices for kicks.
To the OP, A bad pressure reducing valve does weird noises etc . it could be that the roaring noises and loud noises

 

[Qiyansun]

Ive never seen a backflow on a house for firesprnklers but seen many many checkvalves. a restuarant or apt complex a differant story. Nothing unusual about no backflow valve on firesprinkler system in single family homes in So Ca. but code could have changed but thousands upon thousands built this way after year 2000 and possibly till now.
My area has RPP on every home with irrigation sprinklers rather than just antisiphon sprinkler valves I dont know why but they arent buying those backflow devices for kicks.
To the OP, A bad pressure reducing valve does wiered noises etc . it could be that the roaring noises and loud noises

The pressure regulator to the house is set to 50 psi and the pressure regulator to the irrigation system is set to 40 psi. Attaching a pressure gauge to either didn’t show the vibrating needle as seen on the fire sprinkler gauge. When shut off water to the irrigation system in order to narrow down the problem, it still happens.

 

[Jeff H Young]

check valve good or bad I don't think is your problem any particular reason you suspect that? too bad we don't have shut off valves to the fire sprinklers but we all know why we don't people would turn them off and never get around to fixing the problem.
changed dozens of PRV though they pretty much all go bad after 5 to 15 years like almost everyone of them

 

[Qiyansun]

The PRVs are just about a year old. When opening the hose bib normally, the pressure gauge needle vibrates and thundering noises from the ceiling. When opening the hose bib slowly, the needle moves smoothly from 65 psi to 60 psi. Closing the hose bib the needle moves back to 65 psi. Why using the house water changes the pressure of the fire sprinkler system? Should the check valve prevent the pressure loss?

 

[Qiyansun]

Anyone seen fire sprinkler system pressure drop when using house water?

 

[Jeff H Young]

sounds like a bad regulator but not betting on it . I had a bizarre one not long ago that I took a gamble ( replaced it) and it fixed it instantly the noise was noticeable at ceiling .
BTW I never pay attention to pressure at the fire sprinklers but I suppose you are getting at possibility of a bad check making noise when trying to remain closed and water backfeeding into the potable water? maybe I never had that problem? how about throwing your old PRV back on and giving it a try?