Pipe banging with arrestor in place, possible diff in pressure in system?

[falconxlc]

Picture above is the current setup and it has a prv (50psi) and feeds the facets and rest of house except for irrigation system. The city water pressure is >90 psi which only feeds the irrigation system.

The prv was installed last November and so the irrigation system never had a chance to be run/tested until now, and we get a series of pipe bangs around the house whenever the sprinkler valves cycle. I added an arrestor between the backflow and the valves, seems to damper the pipe banging a little but does not silent the pipes. Prior to the prv install, there was no pipe bang/hammer issue with city water pressure. Reason for PRV was for lowering pressure for showers and faucets and water heater expansion tank.

Whats the reason for pipe bangs even with water hammer? Is it due to city pressure and prv alternating the house pressure? Did we install the prv at the wrong spot? should the prv be placed after the shutoff to service all including irrigation? if we installed a second prv going to the irrigation, could this also solve the problem ?

Any responses would be greatly appreciated.

 

[Jeff H Young]

Water hammer arrestors are not water hammer fixers they help soften but no guarantee.
Im not an Irrigation specialist but have hooked up sprinklers on the reduced pressure side and on the high side.
If irrigation is sized ok 50 psi might be fine
loose pipes in walls , undersized piping , are 2 things that cause a hammer, the best way to avoid a water hammer is by good workmanship in my opinion. installing water hammer arrestors after the fact to fix a banging pipe issue is the easiest fix and with a little luck problem solved but I find it fixes completely less than half of the hammer issues Ive encountered

 

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[falconxlc]

Thanks for your reply.

I did another test where by, i turned on a kitchen faucet while the irrigation system was running (cycling zones) and there is no water banging/pipe banging at all. Makes me think the high-pressure town water is having a vacuum effect on the PRV-sided pipe. And when the sprinkler zone is turned off, the inrush pressure to seal the vacuum creates the banging.

If i move the PRV to before the Tee split (home vs irrigation), at 50psi it can serve both home and irrigation. I just hope 50psi is enough to service 6 zones with each zone having 5-7 rotor heads.

If you have additional comments or what i said was not correct, i'd love to hear them. Ty.

 

[Fitter30]

Need to look at the factory web site for max flow of the prv . Backflow devise will also reduce line pressure around 10 lbs.

 

[Jeff H Young]

flow rate on prv would only come into play if you decide to connect it to the irrigation.
is your main line from the street a long run ? only 3/4 inch or 1/2 ? meter in basement old galvie line from street or a small pipe ? the stop valve at street open all the way?
a long run with old galvie pipe rusted halfway closed opf small diametor pipe leads to a massive pressure drop when a heavy load is run and will cause hammering,

 

[falconxlc]

main line is 3/4, water meter is relatively new only 8 yrs old. the whole house is 20 yrs old, all copper pipes.

the sprinkler tee is 1inch tho.

when the kitchen faucet is not opened all the way (half opened), we get the hammering, but if its opened all the way no hammer.

 

[falconxlc]

Seems the problem is resolved when the PRV pressure is upped.

Likely due to the difference between restricted PRV pressure and varying city pressure, the differential of the two was creating low-pressure/vacuum in the pipe and when the valve shuts the pressures need to equalize and thus creating the banging. The higher the differential the louder the banging. After adjusting the PRV to be within 30 psi of the city pressure the banging is still there but is so low that there is no audible noise unless u are watching the pipe.

Thanks all for your inputs, and glad this was resolved without adding/modifying any piping.