I should mention that I know nothing about irrigation systems. This was all installed by my landscaper, so I've been assuming he used the cheapest valves that would do the job. Here's a photo - would the black screw be a flow control? I know I can use it to open or close the valve, but I'm not sure if it's a flow control; I was planning on fiddling with it this weekend to see. The valve says "orbit" on the side.

I actually have 5 valves in all, but it's only the three valves for my grass sprinklers that cause the water hammer. The other two are for drip irrigation and haven't been any problem, probably due to the lower water draw.

{{gwi:333490}}

The black screw is a manual bleed screw. The valves you have don't have flow control. Orbit is an economy brand.
If it were me, I would try one thing before replacing the valves, due to the fact that the landscaper who installed the system didn't do you and favors in his installation techniques. It appears from the pic that the valves are very close together and will require some tricky replumbing for the layman to replace.
I would drain the entire house plumbing system to try to refill the air chambers which act as a cushion for water hammer. Turn off the water to the house at the house, then turn on all the faucets, hose bibbs ect. then reverse the process once fully drained by closing all the things you opened. This will refill the air chambers with air in case they have somehow been filled with water instead of air. Turn the water back on to the house and turn the sprinkler system on and see if the water hammmer situation improves.
It is also possible that when the system was installed that the irrigation main was backfilled in such a fashion that it rests on the main to the house, which is the worst senario of all in that you really have no idea where the two pipes touch each other under the ground.

Good luck!

All Wet
Texas Licensed Irrigator #1897 since 1984

all_wet, thanks for the suggestion. I actually have two hammer arrestors at the main setup. One's the air-charged stovepipe that you're referring to, the other is a traditional store-bought rubber diaphragm (and at this point I know way more about water hammer and arrestors than I ever wanted to). The stovepipe didn't do much, so I had another plumber install the regular type (top right in the photo). Below is a photo of the main setup.

The house plumbing is on the branch with the PRV on the left. The irrigation is the PRV to the right. The stovepipe is on the fire sprinkler line.

This all started when that little drip pipe started flowing water non-stop. Turned out that's the overflow pipe for my fire sprinkler system, which has a valve that opens at 175psi. The unregulated water pressure is typically around 120 - 160, so it doesn't take much of a spike to pop the valve. The fire sprinkler must remain unregulated per code.

The arrestor has eased the hammer enough that the valve no longer pops open regularly, but I still hear the pipes go "bang" each time one of the sprinkler valves closes. The sound is from inside the walls, so that makes me think it's not from pipes hitting outside the house.

I'm perfectly willing to pay a sprinkler company to replace the valves if any of the pros here have experience with them and think they really do prevent water hammer. God knows I've spent enough on plumbers to redo the whole setup you see here, and add the arrestors. This has been a vexing problem for a year now, but I think little by little I've been winning the battle and I think this might just be the last step I need.

{{gwi:333491}}

From what I learned recently, all sprinkler valves have a slow closing feature built in. Filling of the space above the diaphram through a small opening takes time. But I suppose there are slower closing valves. Can you put another water hammer arrestor in the sprinkler line, because that seems to be easier than replacing the valves?

By the way, I put those arrestors on clothes washer and all bathroom flush bowls. I think I have about 5 of these, in addition to the conventional risers. But I still have small water hammering from a loose (unsupported) pipe above the ceiling. You may have the same problem. A section of the pipe may be loose behind the wall. But I have to say that adding those 5 arrestors alleviated water hammering a lot. Good Luck!

I have no experience with trying to fix water hammer, but what I know about the subject came from irrigationtutorials.com and my intuition (mechanically inclined, degrees in engineering, etc).

I wonder if the problem is with the hammer arrestor being at the back of the irrigation system rather than the front.

Here's my line of thinking...

Water is an incompressible fluid, so rather than picturing it as a continuous fluid, think of it in terms of "pieces" of water pushing each other through the pipe. When the irrigation valve suddenly closes, the first piece (we'll call it P1) still on the back side of the valve crashes into the valve. That piece of water was travelling at about 3-4 mph and suddenly came to a stop. Since the water has no where to go, it causes a pressure spike in the pipe that surrounds it. Now water piece P2 behind P1 crashes into P1. P2 causes a similar pressure spike in the pipe around it when it comes to a sudden stop. Then the same occurs with P3, P4, P5, P6... until we get to P1252145 back at the water hammer arrestor. Now P1252146, rather than crashing with a sudden stop into P1252145 partially pushes it's way into the "spring loaded wall" of the hammer arrestor. Now when piece P125247 and everything behind it all get cushioned by the hammer arrestor. In the meantime, water hammer and stress on the pipes has already occurred on all the pieces between P1 and P1252145, so you still hear a bit of the water hammer from all those pieces.

Now if we move the arrestor closer to the valves, fewer "pieces" of water are involved in the "wreck" before the spring loaded cushion of the arrestor is reached and less water hammer is heard as a result.

Is there still enough pipe at the end of the valve manifold for you to add another arrestor there?

Just to close this thread out, I got new valves installed today and they totally fixed the problem. I used the Rainbird PGA series valves, which Rainbird says are slow-closing to prevent water hammer. I did pay a pro to do the install based on comments from all_wet. Finally, after about a year of futzing with this problem, I'm a happy camper.

Uh oh I'm scared now, I put in 2 of those 3 valve Orbit manifolds. Havn't had any issue with watter hammer with them, the main valve is a rainbird valve, maybe it closes first. I figured they were cheap when I broke the manifold installing a poly-pipe. I had one valve that is backwards! It is on when the black knob is closes and off when open. When the signal is sent to it it turns it off and when it has no power it opens the valve. I bought a new orbit manifold so I could swap the valves and take it back to evil orange hah. Maybe I shouldn't have been so cheap and bought the hunter manifold for an extra $20 well maybe I will on the backyard next year atleast :)