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Mach1
04-19-2007, 06:59 PM
Hello all,

I have a residential sprinkler system that I installed myself last year. From browsing the forums here, I can see that I will take some flak for using Rainbird parts from HD. I will claim ignorance, I thought they were all the same quality parts.:confused: I didn't know any better. Despite that, the system works well and has good coverage on my 1/4 acre lot.

I am having trouble with waterhammer when switching zones. I have 1" PVC feeding the valve boxes, and some of the runs are pretty long from the source to the valve boxes. My zones use 12 to 14 GPM depending on which one is running, static water pressure is 62 PSI.

I did not install a master valve on the system, and I'm wondering if that might help? The pipe runs basically the length of the house before exiting outside, so I wonder if a master valve would be a good idea even if it dosen't help with waterhammer?

Just wondering if anything can be done to get the hammer:hammerhead: under control before something bad happens!
Thanks,
Joe M.

Let-it-mow!
04-19-2007, 07:17 PM
You probably already know but water hammer is caused by the water in your pipes slamming into the valve when it snaps closed. The moving water acts like a heavy, fast moving solid and it really hits hard when it's forced to stop almost instantly.

If you install a "Water hammer arrestor" you will solve the problem. This is installed on the supply side of the offending valve. It has a cushion of air inside. When the valve closes, some of the water will enter the chamber and this cushions the blow.

http://pexsupply.com/img/categoryImages/Watts-150A-Water-Hammer-Arr.gif

Mike Leary
04-19-2007, 07:38 PM
The arrestor is a good idea.....Rain-Bird valves are usually slow closing, but you may have "a made elsewhere" valve..the gpm seems fine for class 200
pipe, but not for sch 40..remember the 5' a second rule.Master valves cool.
Let-it-mow....great quote....I've been guilty of doing that to to our "bottom
feeders" too; didn't take them too long to catch on!

Mach1
04-19-2007, 10:03 PM
The valves I used are Rainbird JTV-100's. It says "Assembled in Mexico by Rainbird" on the box.:cry: They close slow but still cause hammer.:hammerhead:

Thank-you much for the tip on the hammer-arrestor. Where's the best place to install it? Close to where my system connects to the main, close to the valve boxes or somewhere in between, or does it matter? Is there any certain size of arrestor I should be looking at?

Thanks again,
Joe M.

Wet_Boots
04-19-2007, 10:15 PM
What's the static water pressure? If the water hammer is resonating throughout the house, it might be possible to fit a pressure reducer in the house supply, and confine the hammer to the sprinkler system.

Mach1
04-19-2007, 10:26 PM
What's the static water pressure? If the water hammer is resonating throughout the house, it might be possible to fit a pressure reducer in the house supply, and confine the hammer to the sprinkler system.

Static water pressure is 62 PSI. I don't have any issues with waterhammer in the house's plumbing, it's isolated to the supply for the sprinkler system. That pipe does run through the basement for quite a ways, so the hammer can be heard in the house.

Joe M.

Wet_Boots
04-19-2007, 10:43 PM
Since water hammer is a function of water velocity and pipe length, it pays to up-size the pipe in long runs. Those hammer arrestors go as close to the zone valves as possible, so the moving water can 'run into' the arrestor.

Dirty Water
04-19-2007, 10:54 PM
Let me guess, the line inside the house is 1/2" copper?

Mach1
04-19-2007, 11:11 PM
Let me guess, the line inside the house is 1/2" copper?

DW, The entire system is 1" pipe. It's copper where it taps in right after the watermeter for 3 feet in to a double-check backflow preventer. It's all 1" PVC after the backflow preventer as well.

Joe M.

Flow Control
04-19-2007, 11:16 PM
Great Quote Mow

PurpHaze
04-19-2007, 11:19 PM
I have 1" PVC feeding the valve boxes, and some of the runs are pretty long from the source to the valve boxes.

All PVC pipe is not created equal. What "class" or "schedule" is the pipe?

Also... are you experiencing water hammer with EVERY zone valve closing or on just select ones within your system?

PurpHaze
04-19-2007, 11:39 PM
Rain-Bird valves are usually slow closing, but you may have "a made elsewhere" valve.

The valves I used are Rainbird JTV-100's. It says "Assembled in Mexico by Rainbird" on the box. They close slow but still cause hammer.

All irrigation diaphragm valves are considered to be "fast closing" valves (as compared to gate, ball and other types of valves) regardless what a manufacturer claims. In general they are "slow closing" for their first 85% of closure and then that last 15% of closure is considered "extremely fast" as the diaphragm slams closed. Some manufacturers have reduced this to a 90/10% ratio but the slam still occurs for a milisecond that brings the flow of water to a sudden stop causing water hammer.

One of the best ways to prevent water hammer is to insure that ALL the piping within the system is properly designed to keep flow velocities under 5 ft/second.

A master valve might work as a dampener but you must insure that the master valve closes before the zone valve or the shock wave isn't properly dissipated.

Another trick is to size all zone valves one size larger than needed; i.e. installing 1" valves when only 3/4" valves are required for a zone's GPM.

You can also run a larger main line than is needed... say 1-1/4" or 1-1/2" when you only need a 1" main line. This slows the water velocity down tremendously.

There are just so many factors involved in water hammer. However, it seems (only a guess) that something like 90% of the water hammer questions brought up on this forum are from people that have a POC in a basement and that the original irrigation main line is run a long distance before it exits the basement.

Mach1
04-20-2007, 12:01 AM
All PVC pipe is not created equal. What "class" or "schedule" is the pipe?

Also... are you experiencing water hammer with EVERY zone valve closing or on just select ones within your system?

It's Schedule 40 PVC after the backflow preventer. All zones hammer.

Joe M.

Mach1
04-20-2007, 12:18 AM
All irrigation diaphragm valves are considered to be "fast closing" valves (as compared to gate, ball and other types of valves) regardless what a manufacturer claims. In general they are "slow closing" for their first 85% of closure and then that last 15% of closure is considered "extremely fast" as the diaphragm slams closed. Some manufacturers have reduced this to a 90/10% ratio but the slam still occurs for a milisecond that brings the flow of water to a sudden stop causing water hammer.

The valves act just as you describe. They close slow at first, then slap shut.


One of the best ways to prevent water hammer is to insure that ALL the piping within the system is properly designed to keep flow velocities under 5 ft/second.

I thought I did that when I designed the system. I did aspire to not exceed 5ft/per second. Perhaps my dynamic pressure is pushing my GPM higher than I thought. I used the published data from Rainbird to figure the GPM.


A master valve might work as a dampener but you must insure that the master valve closes before the zone valve or the shock wave isn't properly dissipated.

I was thinking the same thing. Unless the MV closed first, I don't think it would help much.


Another trick is to size all zone valves one size larger than needed; i.e. installing 1" valves when only 3/4" valves are required for a zone's GPM.

The JTV-100 is a 1" valve.


You can also run a larger main line than is needed... say 1-1/4" or 1-1/2" when you only need a 1" main line. This slows the water velocity down tremendously.

Good advice! It would have been easy to do when I was installing the system, but hard to do now. I think I considered it, but didn't see any benefit since my POC is all 1". I see the error in that now.


There are just so many factors involved in water hammer. However, it seems (only a guess) that something like 90% of the water hammer questions brought up on this forum are from people that have a POC in a basement and that the original irrigation main line is run a long distance before it exits the basement.

My situation *exactly*. There's about 60 feet of line in the basement prior to it exiting the house.

Thanks,
Joe M.

PurpHaze
04-20-2007, 12:27 AM
My situation *exactly*. There's about 60 feet of line in the basement prior to it exiting the house.

It's Schedule 40 PVC after the backflow preventer.

PVC pipe is "elastic" and can accentuate water hammer. Probably could have used 1-1/4" CL 315 and things would have been a lot different.

All zones hammer.

If the valves have flow controls on them then try closing the valves down a little.

Rotor_Tool
04-20-2007, 12:31 AM
Just to clarify, these JTV valves are assembled in AZ, by domestic labor forces. The only difference is the color of the plastic used on the bonnet.

As far as the water hammer is concerned, you should really take a look at your water velocity. The valves are reverse flow, which is what causes the valve to "slam" shut, this is a safety mechanism to prevent flooding if a valve were to fail.

Mach1
04-20-2007, 01:26 AM
Just to clarify, these JTV valves are assembled in AZ, by domestic labor forces. The only difference is the color of the plastic used on the bonnet.

As far as the water hammer is concerned, you should really take a look at your water velocity. The valves are reverse flow, which is what causes the valve to "slam" shut, this is a safety mechanism to prevent flooding if a valve were to fail.

I bought a couple of extra valves in case I had any failures. I don't want to start a flame war, but it says "assembled in mexico by rainbird" right on the box it came in.

Joe M.

Mach1
04-20-2007, 01:30 AM
PVC pipe is "elastic" and can accentuate water hammer. Probably could have used 1-1/4" CL 315 and things would have been a lot different.

If the valves have flow controls on them then try closing the valves down a little.

Thanks for the reply. This particular valve does not have flow control on it. My best option is probaly going to be adding hammer-arrestor chambers.

Joe M.

PurpHaze
04-20-2007, 09:06 AM
Let us know how things turn out Joe.

Ground Master
04-20-2007, 10:31 AM
I've had good luck with the Rainbird PEB's-they are a slower closing valve.

DanaMac
04-20-2007, 10:33 AM
I've had good luck with the Rainbird PEB's-they are a slower closing valve.

I agree. And the one that causes the most problem with hammering that I've found, is the RB DV-100.

Ground Master
04-20-2007, 10:39 AM
The hunter entry level valves are also slower closing.

Wet_Boots
04-20-2007, 10:55 AM
The Imperial Crown valves could take a special 'slow closing' orifice fitting, to replace the standard one. Surprising that no one else ever picked up on the idea. I'll still give Toro valves props for their slow-closing characteristics.