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Green Sweep
09-16-2004, 07:33 AM
I have a system that we installed 3 years ago that has been experiencing teribble water hammer all summer. The system never did this before. There is a 3/4" copper main line that is T'd inside the house & exits the front & back. There are 2 master valves feeding 1" mainlines which feed 12 zones with 1" laterals (all PVC). All valves & heads are Rain Bird & the system runs @ 100psi. We have already: Replaced both master valve diaphragms, installed 2 water hammer reducers on the copper inside. Neither of these did a damn thing to stop the water hammer. My next 2 options are: Replace all diaphagms (but why? the system is only 3 years old!), Or add SAM fittings to every head to prevent the water from draining. Has anyone out there had similar problems? If so, I'd appreciate your input. This lady has been a saint (I would have been really ticked). She has a newborn baby & has had to listen to an AK-47 in her basement every other day at 6:30 in the morning.

DanaMac
09-16-2004, 09:23 AM
100 psi seems high but if that is the way you designed it for installation, lowering it may affect performance. You could try it though. Put in a PRV (pressure regulating valve) and reduce it to 80 or 90 psi and see if that helps and also allows the zones to function properly.

You also mentioned the valves are Rainbird. I have had many problems with Rainbird DV-100 valves shutting off very fast and creating water hammer when they shut off. I have seen manifolds blow apart due to it, even at 60-70 psi. So I no longer use DV valves. One thing that seemed to help though, is swapping out the top of the valves to make them a flow control top, and then reducing the flow slightly. I have had that work sometimes and not on others. Are the DVs rated for 100 psi? Don't have my specs in front of me.

You might also take apart the PVB or RP and see if anything is damaged inside(check valve) that could be disrupting things. Hope you get it, I hate those nagging ongoing problem jobs.

jerryrwm
09-16-2004, 10:22 AM
The "design" pressure sounds excessively high. Which means that the static pressure must be high also. House sitting at the bottom of a steep hill?

The equipment you are using is fine. The DV valves are rated for 150 psi as are just about every plastic valve on the market. They will as DM said, create water hammer, but so does every valve on the market. The closing time on any valve is mainly dependent on the velocity of water, which is affected by the pressure pushing it. Lower the pressure, slow the water, reduce the water hammer. Good solid cement welds on the fittings reduces manifold blow-outs.

Changing out heads to SAMS will not solve the problem. Sprinkler heads are their own water hammer arrestors. The water hammer problems you are experiencing is between the zone valves and the master valves, and between the master valves and city main.

Sounds like the whole house could use a pressure regulating valve before it enters the house. Set at under 75 psi. Can't think of too many reasons why a residential irrigation system would need to be design for over 60-70 psi.

Also, you may not have sized your water hammer arrestors properly, or you need more. Check manufacturer's spec on the flow/pressure that they are rated for. You may need to add several more along the line.

Jerry

DanaMac
09-16-2004, 10:27 AM
Jerry - I know what your saying, but I have also taken care of the problem by replacing DV valves with other valves - Irritrol or Hunter. I don't see those valves shuting down as fast, causing that hammer problem. They tend to shut down "softer". Maybe not slower.

Green Sweep
09-16-2004, 07:49 PM
Thank you guys for the input, that was exactly what I was looking for. To address the psi issue, most of our systems run on 60 - 70 psi. We do have a few at 100 psi or more & we roll with it. We were thinking of adding a PRV as a last resort. The system runs beautifully now & really did not want to altar that. However, I think that only minor nozzle adjustments would be needed. Jerry, the house sits on top of a hill & I got the SAMS idea because the hammer seems to be loudest on zones along the street at the bottom. I theorized that the water rushing down the hill at that velocity was causing the pipes to really shake. But, if that were the case, the water hammer would not have taken 3 years to start. Also, the pipes are shaking when the valves are opening, not closing. I know this because I ran the system with a 10 second delay between zones while standing at the meter. My last question is why 3 years? If too much pressure is the issue, then why did it take 3 years to start water hammering?

SprinklerGuy
09-16-2004, 09:54 PM
I feel your pain..many times I have asked the question "why?"

At 100psi are your nozzles fogging excessively? I would think they would be...not optimum by any stretch. If it works well at 100psi, I'm guessing it will work even better at 60...unless of course the system wasn't designed properly and you need 100 psi to get the coverage you need.

Which seems a bit funny to me...I don't think heads work better or throw farther at 100psi...they may appear to..but I bet they fog more than they should.

Good luck

Critical Care
09-17-2004, 12:43 AM
I've been using Hunter HPV valves that close slowly to supress water hammer. I wonder if they could solve your problem. I'm a bit curious as to how much water, gpm, you have flowing through the 3/4" copper and into the 1" mains?

Had a slight hammer problem with a large 2" Irritrol "normally open" master valve designed to shut off a field irrigation system whenever the house irrigation was turned on. From reviewing the flow rate specs on the 2" valve I feel that I could have gotten away from the water hammer (perhaps) by downsizing the valve to 1 1/2".

MikeK
09-17-2004, 01:32 AM
Since water hammer is a function of pressure, it's my guess that the high static water pressures are causing the problem. Could it be that the water pressure in your area increased in your area since the system was installed?
Install a pressure regulator and while you are at it, do it in such a way that it regulates your domestic water supply as well as the sprinkler system.
I am guessing that toilet and faucet vlaves do not live to long exposed to 100 PSI.

jerryrwm
09-17-2004, 03:37 AM
I gotta agree with MikeK. The static pressure is extremely high and that diaphragm is fluttering it's a$$ off to open creating the hammer vibrations. I would also guess that the faucets in the house will almost take the glass out of your hand when you open them. And that commode tank probably gets filled pretty quickly too!

I still would recommend a PRV on the service line. Hell they are only about $65.00 for a 1" and time to put it in is minimal.

As for the three year period before it showed up as a problem. What has changed in the area? More houses or added subdivision that might have put in newer distribution lines to the area replacing older and smaller lines. Or maybe the utility district added a pump station or two, or upgraded their pumps? Usually something that happens after a long period of time is more externally caused.

Hope you get it sorted out.

Jerry

Green Sweep
09-17-2004, 01:07 PM
Our plumber is scheduled to install a PRV next week. Will keep you posted.

Ric
09-17-2004, 03:40 PM
Since water hammer is a function of pressure, it's my guess that the high static water pressures are causing the problem. Could it be that the water pressure in your area increased in your area since the system was installed?
Install a pressure regulator and while you are at it, do it in such a way that it regulates your domestic water supply as well as the sprinkler system.
I am guessing that toilet and faucet vlaves do not live to long exposed to 100 PSI.


Mike

Water hammer is a function of velocity not necessarily pressure. Pressure will increase velocity. It is the sudden stop of a high volume of water flowing through pipes that causes an increase in pressure that causes water hammer. If that sudden increase is above the pressure rating of the pipes it will break them. Larger Pipes can flow a larger volume of water at a slower speed. This of course is why we try and size pipe to handle the water volume. Valves that turn off slowly reduce water hammer because they limit the sudden stop in the flow of water.

Once again with out seeing the total system I can only guess at the problem. Since this system was working without Water hammer, Could some one of changed the spray heads to larger volume size? and could the city water pressure of increased over the years? I personal use 1 1/4 mains or bigger on 4 to 6 zone systems. on a 12 zone I think I would want at least a 2" main even if the zones run one at a time. Most 12 zone system I see have a large number of heads.

Green Sweep
09-17-2004, 04:59 PM
Gentlemen,
After reading your input, I had the owner go through the files to see if he documented the pressure during the original installation. He did - 65 PSI!!! That explains everything. This is one of the most rapidly growing communities in Pittsburgh & it makes sense that the water companies are accounting for that. It also gives me a legitimate reason to bill for the time that I have spent looking at this system. Troubleshooting - huh? Sometimes there are simple answers in the office. Thanks so much for all of your help.

Rob

jerryrwm
09-17-2004, 07:31 PM
Once again with out seeing the total system I can only guess at the problem. Since this system was working without Water hammer, Could some one of changed the spray heads to larger volume size? and could the city water pressure of increased over the years? I personal use 1 1/4 mains or bigger on 4 to 6 zone systems. on a 12 zone I think I would want at least a 2" main even if the zones run one at a time. Most 12 zone system I see have a large number of heads.

Not wanting to sound stupid, but could you tell me what the number of zones has to do with the size of the mainline? Especially on a residential or small commercial property.

Pipe sizing is done for one or more of three reasons. (not in any order)
1. For cost - smaller pipe where it can be used lowers materials cost. You could pipe the entire system in 2" pipe and it would work fine, but the added expense would be cost prohibitive.
2. Reduce pressure loss due to friction - larger pipe for larger flows or long lengths of run
3. Reduce velocity and potential damage - larger pipe slows the water reducing the effect of water hammer.

But since most residential systems do not have the available water supply to run multiple zones simultaniously, the need for mainline oversizing is eliminated. Most houses have a meter that will supply 12 - 18 GPM. Friction loss for 11/4" pipe @ 25 gpm is 4.4 approx and the velocity is 2.2 approx. Well within industry standards and manufacturer's recommendations. At 18 GPM it is 3.3 psi loss and 1.2 velocity. There is usually no need to go any larger on the typical residential yard.

Now, the question comes about the number of zones dictating the mainline size. What bearing does this have on the operation of the system?


Just wanting clarification.

Jerry R

Ric
09-17-2004, 10:27 PM
Jerry R

I use 1 1/4 inch and even 1 1/2 pipe for my mains and the start of my laterals for all the reasons you stated. On 4 to 6 zone systems there are generally enough heads to justify the water usage. Laterals are of course down sized to save money as they get further away from the main. Maybe my area has more water available than yours. Because I can install 12, 570's on a zone and get plenty of pressure. I can run 7 to 8 gear-drives on a zone.

12 zone systems in my area are generally large condos or commercial building which once again have many heads. Most of these heads are gear drive and have a large GPM flow. These building also have commercial water supply and can handle 2 inch mains.

In my nursery I use a 2 inch Mains under ground and 1 1/2 laterals on top of the ground. These laterals are being for ever changed or added on to. I have as many as 30 heads on one zone, however I use hydraulic valves which are very slow closing. They also have the advantage of being able to be placed very far from the controller without the need increased wire size. Doesn't matter whether they are 5 or 5,000 feet away, they still use the same size tubing.

Now my business is really landscape install and a retail nursery. However I have a irrigation and pesticide license. I only install irrigation on property That I do the landscaping on. I only do Irrigation repairs for my present customers. So I try and make sure the system I install is over sized and can be added on to.

Critical Care
09-18-2004, 12:55 AM
I think, Ric, it doesn't really matter how many heads you have on a zone, but rather what their total demand is in g.p.m. Some controllers allow for more than one zone to be in operation at once, such as a drip zone to be concurrent with another zone, but still the pipe size is relevant only to the demand that will flow through it. If you can have two 15 gpm zones operating concurrently then for sure you better have a 1 1/2" or 2" main.

Rob, wow... they increased the pressure. I generally see the opposite, especially in areas that have a lot of new growth. And, you know, flows of more than 6 gpm through 3/4" K copper gets into the shaded area with rates over 5' per second. If the irrigation demand is 15 gpm, then the velocity in that 3/4" line is about 11 feet per second (whoa Nelly!), and at 11 feet per second you actually have a pressure loss of about 30 psi. Am I seeing this wrong guys???

jerryrwm
09-18-2004, 02:22 AM
Rob, wow... they increased the pressure. I generally see the opposite, especially in areas that have a lot of new growth. And, you know, flows of more than 6 gpm through 3/4" K copper gets into the shaded area with rates over 5' per second. If the irrigation demand is 15 gpm, then the velocity in that 3/4" line is about 11 feet per second (whoa Nelly!), and at 11 feet per second you actually have a pressure loss of about 30 psi. Am I seeing this wrong guys???

No, that's correct for copper...but velocity in copper pipe or other metal pipe doesn't fall under the 5 fps rule. That 5 fps is for plastic PVC or Poly. Copper pipe joints are typically soldered and therefore stronger than solvent weld joints. And the pressure loss in copper is extremely high. Not as high a friction coefficient as plastic pipe.

Also, velocity really is only a problem when it is in a contained piping, such as between the section valve and the backflow preventor. This is when the piping and fittings have to absorb the shock waves to dissipate the energy. On the lateral side of the valve, the shock waves are quickly dissipated as the water is forced out of the open heads, or drip emitters. On agricultural drip systems they frequently design the lateral headers with velocities of 8 - 10 fps and those lines last for a long time.

Planter
09-18-2004, 02:59 AM
The Hunter Technical Manual lists this formula for water hammer:

P(sub t) = P(sub o) +((V x L x 0.07)/t)


Where:
P(sub t) = the total pressure developed, in psi
P(sub o) = the operating pressure at the time of valve closing, in psi
V = velocity at the time the reduction in velocity occurred, in feet per second
L = Length of straight pipe between source and point where reduction in velocity
occurred, this would be the longest section, in feet (straight pipe means
no tee or ell fittings)
t = seconds during which the velocity was reduced, for example, a valve that closes
in a half second would have a value for “t” of 0.5
0.07 = constant used to convert velocity, length and time into pressure

Critical Care
09-19-2004, 02:34 AM
Uh huh, Planter. I haven't run across that formula, but it adds up. It would be interesting to put some figures into that formula to see what we have. I'm still thinking about L, the length of pipe figure...

And, the 100 psi service pressure surely must be static, the home is on a hill, with 3/4" copper, and who knows how long of a run of that. The dynamic pressure is bound to be considerably lower.

I was also trying to think about what happens when you have a high velocity rate going through 3/4" copper and then into 1" pvc. Does the rate simply drop off while maintaining the constant flow rate of whatever-it-is gallons per minute? Umm... an inverse linear relation to pipe size? Geeze, it's too late for this.