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SNG

New Member

1

Saturday, June 5th 2010, 6:37pm

Thumping/Knocking Noise in Pipes for a Few Seconds when Valve Opens/Zone Comes on

Hi - We moved into our house 2 years ago. For the first year, the sprinkler system worked without any problems. The next year, the knocking started. Most (but not all) of the time, when a zone comes on and the water starts flowing, there's a loud "Thump thump thump thump" sound that comes from the main sprinkler line from the house, for maybe maybe 2 seconds. After that, it's fine until the next zone starts - then, more thumping. We had a plumber look at our PVB, and it's working fine. We had a sprinkler company check the valves in the irrigation control box and they were fine. Another sprinkler company suggested replacing our lowest sprinkler heads (since our yard is sloped) with heads that have built-in anti-drain valves, so that leaking water from the heads won't cause the pipes to partially fill with air. We tried this, and we still have the thumping. Has anyone heard of this problem, and a way to solve it? Every company we talk to seems baffled. I don't think it's water hammer because that is something that happens when water stops - this happens when the water starts moving.



Our main water line is a 1" copper from the meter. A 3/4" copper tees away toward the sprinkler system, and the tee is just before a PRV on the 1" mainline. I think the static pressure is 90-100 psi from the street, and the PRV reduces the house pressure to 60 or so. However the full pressure goes toward the 3/4" sprinkler line - the plumber said this is how it should be. The sprinkler line goes into a PVB and then splits into 4 zones. Zone 1 is 4 fixed spray heads, zone 2 is 8 fixed spray heads, zone 3 is 4 rotors, and zone 4 is 6 rotors. The thumping is worst when zones 3 and 4 turn on. Zone 4 is the worst.



Any advice is greatly appreciated. We could almost live with the noise, but we're worried the pipes are slowly being damaged.



Thanks,

Steve

Wet_Boots

Supreme Member

Posts: 4,026

Location: Metro NYC

2

Monday, June 7th 2010, 8:46am

You are experiencing an oscillation. New valve diaphragms might cure it. The problem has its basis in a zone's flow being excessive in relation to the supply.

SNG

New Member

3

Monday, August 2nd 2010, 10:40pm

Valve diaphragms did not fix it - Do you think that it could be that the static pressure of 90+ psi is too much for the system? One sprinkler company suggested that this is too much for a sprinkler system to handle, and that I should install a new pressure reducing valve on the irrigation line, to reduce the pressure to more like 75 - 80 psi. I'm about ready to try that, but I don't want to spend hundreds on a plumber if it's just a shot in the dark. Any thoughts?

Wet_Boots

Supreme Member

Posts: 4,026

Location: Metro NYC

4

Tuesday, August 3rd 2010, 7:45am

Is it possible to reduce flow in the zones? Is it possible to add check valves to each individual head? (make and model of head, please) ~ Your problem comes from water that is rushing into an empty zone. Slow down that rush, and your problem goes away.

SNG

New Member

5

Tuesday, August 3rd 2010, 8:43am

I'm not sure the make and model of the existing heads - whoever lived here before installed them. I recently replaced the lowest heads in Zone 3 & 4 with new Hunter rotors with built in anti-drain check valves, thinking that might solve the problem, but it didn't. The front yard has pop-up spray heads, not sure the make.



How could i go about reducing flow in the zones?

Wet_Boots

Supreme Member

Posts: 4,026

Location: Metro NYC

6

Tuesday, August 3rd 2010, 9:05am

Another possibility is to up-size the sprinkler supply, with the idea of reducing the effect of the large amount of water rushing through the supply line. Of course, in copper, this is an expensive solution. You see this phenomenon in systems fed from smaller-diameter plumbing far more often than from larger-diameter plumbing.

-

Of course, the idea of installing a pressure reducer in the sprinkler supply, assuming you can stand to lose the pressure, has value in that a lower supply pressure can't produce the same initial flow that the higher pressure can.

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Beyond anyone's budget, are specialty valves that contain the means to prevent fluctuations. They don't open fully until the downstream pressure has risen to a set point.

-

Reducing flows is as simple as changing nozzles on sprinkler heads. Experiment with a single zone first, that has all check-valve heads.

SNG

New Member

7

Tuesday, August 3rd 2010, 10:57am

Well, there's already a 3/4 inch copper supply line - I'm hesitant to go replacing that unless it's a surefire solution.



What do you think about replacing the valves with ones that have flow control? I've also seen pressure regulators that can be installed on the valves. In your opinion, is it more of an issue of high pressure, or high velocity?

Wet_Boots

Supreme Member

Posts: 4,026

Location: Metro NYC

8

Tuesday, August 3rd 2010, 6:53pm

Flow control valves are a good idea, since they can be throttled down, and that will slow a rush of water. Unfortunately, this isn't an easy problem to deal with, especially since it is mostly the result of poor system design.

hi.todd

Supreme Member

Posts: 412

Location: Houston, Texas

9

Tuesday, August 3rd 2010, 9:11pm

You said that the diaphrams did not fix the problem. What is the valve make and model that you changed the diaphragms? How many diaphragms did you change? Is there a Master Valve you can tell this by the controller? What is the model of the Rotor Heads you are using and what is the nozzle in there? Rotor heads will use more water or Gallons per minute the higher the water pressure. If you have High water pressure and you nozzles would use 2 gallons per minute with 50 PSI they will use 6 gallons per minute at 80 PSI. This is just an example, but you get the idea. If you are exceeding the recommended flow through your pipe size you will get the water hammer. 1 inch pipe should only flow 15 or so gallons off of the top of my head. 3/4 pipe should flow up to 10 gallons per minute off the top of my head. 1/2 inch pioe should flow 5 gallons per minute off the top of my head. Also you don't want the water in the pipe to flow faster than 5 feet per second. This is why the pressure and nozzle selection is so important in how many gallons per minute is flowing through your pipes. The cheapest way to fix it is to buy new rotor heads and use the nozzle that has a chart that can tell you how many gallons per minute are flowing with your high pressure and stay with in you pipe size flow chart recommended flow as I have outlined above. The next is to use flow control valves. You probably need new heads anyway. Unless this all started when you changed the heads or paid somebody to change the heads that did not know what they were doing.

Good Luck :thumbsup: :thumbsup: :thumbsup:
:thumbup: :thumbsup:

SNG

New Member

10

Tuesday, August 3rd 2010, 10:37pm

I found another possible solution online - What do you all think of this idea?



http://www.rilawnsprinklers.com/blog/2009/07/noisy-pipes-when-irrigation-system-is.html



It seems to describe exactly what I'm experiencing. (The paragraph on "System is making a loud noise when the zones are starting, then the noise goes away until the next station/zone starts or only on specific zones.")

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