interesting problem with water hammering

I just ran into my old boss. He is now retired, and an avid gardener. He put in a 12-zone automated watering system, and there is a problem in it which is driving him bonkers. I'm posting this because you guys know everything worth knowing.

His water system starts at the meter, then it runs to a tee, and off of one leg goes his entire outside watering network. The other leg of the tee goes to his house. Where the water enters his house, he has a pressure reducing valve. On the outside watering leg, there is a backflow prevention valve to ensure that even in the event of negative city water pressure his gardening water can never wind up in his neighbor's water glass.

At 4AM his watering system turns on. When the first zone valve cuts on, the water pipes *in his house* begin hammering loudly. Eventually it dies down and then the first zone valve cuts off and the second one cuts on, no more problems. But the water hammering wakes him and his family up every morning, and they worry about it damaging their house piping because it sounds so violently loud.

They have had the water department guys out to check his pressure reducing valve, his backflow prevention valve, and the water pressure everywhere, and they say everything checks out OK. He has had two different irrigation consultants come out and other than suggesting things like reprogramming to try a different zone valve to come on first (didn't help) they were similarly unable to come at the root cause of the problem, nor could they suggest a workaround.

I don't really understand the phenomenon of water hammering, but I do understand that it is a pressure oscillation which is characteristic of an underdamped mechanical system. I suggested that he try adding resistance (some kind of flow reducer, maybe a gate valve) or capacitance (one of those bulb thingys) but he is on fire to find the actual root cause and solve it, not just find a workaround. I suggested he try shutting the gate valve, the main water shutoff valve to his house, about 95% tonight to see if the added resistance might do the trick.

Anyone got any bright ideas? This guy is no dummy; he was an engineering manager and has a EE degree from Rensellaer Polytechnic ..

Grant Erwin Kirkland, Washington

underdamped

The only sure way to get rid of 'water hammering' is to install a vertical run of pipe with a cap on the top end. Air trapped in the pipe acts as a cushion and the hammering problem is resolved. Since the hammering occurs on his 'house side' then this 'air trap' needs to be added someplace in that circuit. Most houses less than 20 years old have these air traps already (on both hot and cold circuits).

Or when the valve is opened too quickly, presumably, anything that causes a pressure spike ..

Good site, not very technical, he and I looked it over together.

GWE

It can also happen when opening a valve too rapidly. Think pulse-jet, it's probably the same mechanism. But the fix is to, as someone else said, puta vertical air-filled column to the pipe in question, to absorb the impulses and smooth them out so they can damp down to zero.

You can buy fancy spring-loaded space age water hammer arrestors, or you can make 'em out of 18" of 3/4" pipe and a cap. The latter works great for my house.

Water hammering is usually caused by suddenly shutting off a fast flow. e.g. You open a valve, the water gets to flowing and, especially if the run is long, there is a fair bunch of kinetic energy in the moving water. Now you quickly close the valve and the incompressible water has to stop NOW. So where does all the energy go?

My suggestion is that what is happening is during the off time the water is draining out of the irrigation system. When it first turns on there is very little resistance to flow - just compressing air in the lines and pushing out the nozzles. When the water hits the nozzle(s) there is a sudden dramatic reduction in flow. See above.

The clue that this is correct is that there is no water hammer when the system switches to the second zone since everything has had a chance to fill up.

Suggested cure: Install a bypass valve that, at first turn on, provides a low flow for long enough to fill up the lines then open the main valve.

Ted

When installing new shower valves and new washing machine valves in my house I made up my own water hammer prevention devices. I just used lengths of copper pipe and caps like everyone else does. I told a plumber friend about this cheap fix compared to the ones at the store and he said that the ones I made will eventually become waterlogged and the only fix would be to drain them. In his years being a plumber he had seen this many times. However, the ones I made stopped the water hammer and lasted at least 6 years before I moved. And the ones in my shop have been working for 7 or 8 years so I'm not sure it always happens. ERS

The reason for the fancy commercial ones is two-fold: 1) they will fit in places where several feet of pipe might be a problem, and 2) the air in the home brew version will slowly dissolve in the water, and the thing will stop working. You can always shut off the water & drain the whole system to get air back in, but why bother?

There are two kinds of water hammer. One is the loud bang you get when a pressure pulse is created by a rapidly opening or closing valve (closing is more common). The other is an oscillation in water pressure that can make the pipes moan or in bad cases go bang bang bang as the water pressure bops up & down. This requires flowing water. Imagine blowing over an open soda bottle, only under water. The big spikes can be handled by pre-compressed piston jobs like the Oatey "Quiet Pipes" sold at Home Despot & some hardware stores. However, eventually the pistons can stick, and they won't work well for low pressure fluctuations. They also make water hammer arrestors with a diaphram that are better for stuff like that, and they can't stick. Those you'll need to get from a plumbing supply place, probably special order.

Doug White (who spent several years beta testing the Oatey devices on a house with low water pressure)

Maybe not...

On the cold side, as the cold water sits in the pipe and warms up, air will come out of it and some will be caught in the anti-hammer pipe and keep it nice and full. On the other hand, the hot water will probably have little bubbles of air in it from the water heater which will likewise fill the anti-hammer pipe. This, of course, assumes that water flows past the anti-hammer pipe. So, for best results, tee the anti-hammer pipe off the line before the last valve... (Things get a little more complicated on a vertical pipe where the flow is downward...)

Jerry

I was always told that you want to put the anti-hammer pipe at the top of an inverted U-bend in the pipe. Reasoning being similar, only "amplified" by the U-bend.

Which always left me wondering: What happens with the anti-hammer pipe is completely full of air, and more gets into the system? Sounds like a good recipe for a vapor-lock situation to me...

You have to design your homemade ones to be easily and quickly drained when the hammer starts up again - 1/2" ball shutoff valve on the inlet, 1/2" garden-hose faucet for a drain, and a 1/4" or 3/8" valve on top for air vent is optional but will speed the draining.

Since this is at the laundry a drain is available, though you may have to remove the washer's drain hose and insert the stub garden hose while draining the arrestors.

Home Despot is stocking the Oatey stored air expansion tanks in the

1 and 2 gallon sizes, meant for handling the temperature expansion caused by hot water heaters after a pressure regulator. They are larger than the little inline 'water hammer arrestors', but the stored air bladder also means they shouldn't lose their charge.

But where's the challenge in a store bought solution? ;-)

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A solution to this problem is to put a tire valve on the top to allow air to be pumped back in.

Steve.

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Is the regulator, one of those in-line 8-gpm 25-psi type? If so, they chatter like crazy, on startup. The regulator, should be as close as possible to the outlet of the anti-siphon valve.

My neighbor had the same problem, I ended up curing it by putting a 1'x1' square loop buried in sand, in the pipe. This does two things, (1) breaks up a long straight run, (2) puts some flex in the system.

I have a 6 zone system in the back & a 5 zone in the front. Each circuit has an anti-siphon valve -> regulator -> Y filter. No problems, the Y filter acts like a small accumulator/snubber.

One night when my water softener went off, I thought the house was caving in. Crawled under the house, to find a hanger on a 40' run to the softener, had come loose.

Good to keep in mind, but hasn't happened in the 8 or 10 years so far, so I'm not going to lose sleep over it. Easy enough to fix, as you say. Maybe it's because I seem to drain the house about once a year to add or change something that can't be zoned off.

Thing is, a professional plumber doesn't want callbacks. Not all homeowners are fine with "Yeah, it'll do that every few years, so just drain the pipe and you'll be fine for more years". They just don't want the pipes to knock, they don't want to have to think about why they do or don't. Kinda like going in for a brake job - you get pads and they turn the rotors. The rotors are flat and not grooved (or even lightly grooved) but they turn 'em anyway. Why? They don't want the Soccer Mom coming back to complain, so they'll do un-necessary work (at her expense) to keep her from bothering them.

It's all about expectations. for 50 bucks, or whatever a set of those would cost, I'll make my own.

Maybe it's just my well pump, but I get plenty of air in the water supply as it is. I have a clear hose that I attach to a faucet for filling the fishtanks (beats lugging water around in 5-gallon pails), and I get a _lot_ of bubbles in it, despite having a good connection to the spigot. Maybe the iron filter process dissolves air into the water, or something, but replenishment of air is definately not a problem in my situation.

Right. The gooseneck spigot I mention above does that if you turn both sides on full blast at the same time, which is why I figure it's an oscillation type thing.

I wonder if having a well and pressure tank takes some of that impulse out of the system. Thinking as an electronics tech, it's a big capacitor, but it's on the wrong end of a long inductor, so I'm not sure that the high-frequency dampening will be significant. But yeah, if you put another cap at the delivery end of the system, that makes the system filter the impulses better. pi-filter, effectively. I think. That class was a _long_ time ago.

I remember hearing once that if the valve closed faster than the time it would take a sound-pressure wave to travel the length of the pipe, they would hammer. I don't know how much length of the pipe you'd consider since really, its flowing all the way from the source.

A few years ago we had a "handyman" redo all the bathrooms. A few months after he'd finished and left, I had reason to open one of the walls where he'd moved a toilet from one location to another. He'd dutifully made up air chambers out of a dead leg of copper like what had been at the original location, but apparently not understanding what they were there for, installed each one HORIZONTALLY. Fortunately, we've never had a water hammer problem, so I didn't bother to fix it. But I know where to look if we ever get a problem.

On the subject of washer hoses, I noticed one day that the hot water hose for the washer had a significant bulge right at the bib, so I immediately shut off the water to the washer, and told my wife that she was NOT to use the washer until I could replace the hose that evening. I figured that I'd really dodged a bullet, since my workshop was directly below the laundry room. When I got home that evening with the new (higher quality stainless steel wrapped) hose and went down to my workshop to get some tools, I noticed that there was clear evidence of water on some of my tools (table saw, band saw, etc.). I went upstairs and looked at the hose and discovered that the bulge in the hose was now a jagged hole. My wife and daughter were looking very sheepish. Apparently, despite my very clear warnings that the hose was about to burst, my then college-student daughter insisted that she needed to do a load of laundry right then. Not having any real idea what she was agreeing to, my wife said OK, just one load. The hose burst within minutes of them turning on the water, as I would have predicted. They were expecting a little leak. What they got was a fire hose flood that completely soaked both of them and flooded the workshop before they could get the (many turn) gate valve closed again. They then dried everything out in the laundry room, went down to the workshop and tried to dry everything out down there, hoping that I wouldn't notice. I said a few things about 60 psi water pressure and flow rates, why I had been very explicit about NOT using the washer, and explained how I now had to go down and dismantle the table saw and band saw to get at the water in the crevices before they rusted any more. I think I was very calm, considering.

Once things had settled down, I replaced the laundry gate valves with one of those double ball valves for laundry rooms that allow you to shut off both hot and cold together with a quick push of a lever. Highly recommended. We leave the water off except when we're actually using the washer. Even though we now have the high quality metal braid hoses, I figure they should last forever since they only see pressure for an hour or two a week. If they do have a problem, it will be when someone is there, and the water can be shut off almost immediately.

Also, my wife and daughter listen to me much better when I issue and edict like that (more or less).

The system is hammering because the various valves are slamming shut and causing a shock wave to go through the system. Very simple to fix! Have him pick up a small 2-5 gal. rubber lined pressure tank from a well supplier. Connect it somewhere near the junction with the yard piping. The simpler fix is to put a blind riser on the system, but they tend to waterlog quickly and resume the hammering. Bugs

Repeat after me: Lockout and Tagout procedures. "It's not just for industry anymore!"

If you don't have a real lockout device for something, you put a big note in front of the item, and the note is taped to something really heavy that isn't going to move.

And the tag is so they know what not to do, and to remind them WHY they do not want to do it. Explained in enough detail (the gorier the better) that they will decide not to, and explaining what will happen to someone who ignores the warning and tries it anyway...

And when you add in children or parents with memory issues, it gets even more important. Tell them not to use something, and they forget in 5 minutes. Leave a big note and lock the power cord inside a toolbox, and they remember.

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