Major Water Hammer Issue

[Jedward]

I'm at a loss - I've tried everything I can think of, so its time to turn to the experts. I've attached a rudimentary schematic to help you understand the general layout of things.

My House is up on a hill, so the street (including municipal water) is probably 15-20 vertical feet below the main floor. Water comes into the house from the street to the basement where I have a main shutoff valve. It then goes up to the ceiling of the basement and tees off to the sprinkler shutoff valve in one direction with the other direction going to the pressure reducing valve and then on to all the fixtures in the house (see image)

When I turn ON a sprinkler station (it doesn't matter which one), I get a violent hammer sound coming from the pipe inside the house that feeds the sprinklers. Sometimes its just loud and scary, but in the fall (not sure why it would be worse in Sept-October) it is clearly dangerous because it causes the walls of my house to shake. It only lasts 5 seconds or so. Subsequent valves don't produce the same result, its always just the first one.

Last year I had the hammer arrestor installed, but it didn't help. This spring I had the Pressure Reducing Valve installed (On the line going to the sprinkler valves) and I've tried lowering the pressure, but the hammer always comes back and I can only lower it so much considering that water is already traveling pretty far uphill to get to the yard.

Last year I also put a foam sleeve around the pipe that is hammering, but that hasn't helped. We now have drywall and insulation in the basement, so I'm not able to access any of the interior parts anymore other than the shutoff valves.

I'm not a plumber or an engineer, but my understanding is that hammer usually occurs when a valve is closed - this only happens when the sprinkler valves open which I guess maybe suggests air in the valves? or is it just that the velocity is changing so quickly? I can't really adjust the solenoids on my valves to open slower, can I?

Any help is greatly appreciated. Sprinklers are probably done for the year, but I'd like to have a plan for next year before we get to it.

 

[Terry]

Hammering while using the water is sometimes a loose washer vibrating. What kind of shutoff do you have on the line? Normally on irrigation I would not expect a shutoff to use a rubber washer.

Water hammer when the water shuts off quickly can be helped with a hammer arrestor.

 

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[Jedward]

The shutoff for the sprinklers is a ball valve inside the house. It only happens when turning on the first sprinkler valve (regardless of which one comes first), lasts about 5-7 seconds and stops.

 

[Valveman]

You are probably filling empty sprinkler lines? When the air is pushed out and the water hits the end it bounces back and causes water hammer. Not letting the sprinkler lines drain out will usually stop the hammer. You can put check valves with 1.5 pound springs on each sprinkler to keep the lines from draining out. Makes winterizing harder, but helps with water hammer when the sprinkler valves open.

 

[Tuttles Revenge]

I think the question alluded to in the first 2 replies is:
Does the noise occur when the sprinkler system first starts to use water? - and indication that as Terry mentions, a loose washer or some component is vibrating as the water starts. I would generally describe this as a chattering

or does it occur a few seconds after? as Valveman suggests where the water velocity reaches the end of its run and slams the end of the pipe

or does it occur when the sprinkler system has stopped using water? Which is more a classic water hammer where when a quick acting solenoid valve closes the momentum of the water is slamming the long run of pipe causing water hammer.

 

[Jedward]

Tuttles Revenge - To answer your questions, It is hard to know if it is exactly when it occurs, but it is either right away or within a few seconds after I start the sprinkler station. I suppose I could replace the shutoff ball valve if you think that it could be a loose washer in that valve, but the hammering is really violent and doesn't seem like a loose washer.

Valveman you could very well be right. There is a lot of steep elevation change in my yard, so I wouldn't be at all surprised that water is draining out, leaving a lot of empty lines. So my next question is this: Do I need to put check valves on every sprinkler? Or could I put one on the main branch for each station near the valve box? Or just one check valve on the PVC inlet to the valve box? It might still hammer, but it would be hammering on the PVC outside the house rather than the copper inside the house - correct? Just trying to avoid digging up every single sprinkler head in my complicated yard...

 

[hj]

You probably have a long water line and the sprinkler opens quickly. Because of inertia, the water in the line takes a moment to start moving, in the meantime the pressure in the system drops to ZERO, but then the water gets moving and the "slug" of water hits the system full force and cause the hammer. The cure it to install essentially a hot water expansion tank as an "accumulator" in the cold water line near the sprinkler system, to maintain pressure in the system until things can stabilize.

 

[Valveman]

Tuttles Revenge - To answer your questions, It is hard to know if it is exactly when it occurs, but it is either right away or within a few seconds after I start the sprinkler station. I suppose I could replace the shutoff ball valve if you think that it could be a loose washer in that valve, but the hammering is really violent and doesn't seem like a loose washer.

Valveman you could very well be right. There is a lot of steep elevation change in my yard, so I wouldn't be at all surprised that water is draining out, leaving a lot of empty lines. So my next question is this: Do I need to put check valves on every sprinkler? Or could I put one on the main branch for each station near the valve box? Or just one check valve on the PVC inlet to the valve box? It might still hammer, but it would be hammering on the PVC outside the house rather than the copper inside the house - correct? Just trying to avoid digging up every single sprinkler head in my complicated yard...

Whatever it takes to keep the lines from draining out. May only need check valves on the lowest heads. I don't think a pressure tank will work as a surge or expansion tank, as the pressure will be zero until the lines get re-filled. When the pressure falls below the pre-charge amount of air in the tank the diaphragm will bounce on the bottom of the tank and may make the hammer worse.

 

[Tuttles Revenge]

Tuttles Revenge - To answer your questions, It is hard to know if it is exactly when it occurs, but it is either right away or within a few seconds after I start the sprinkler station. I suppose I could replace the shutoff ball valve if you think that it could be a loose washer in that valve, but the hammering is really violent and doesn't seem like a loose washer.

Valveman you could very well be right. There is a lot of steep elevation change in my yard, so I wouldn't be at all surprised that water is draining out, leaving a lot of empty lines. So my next question is this: Do I need to put check valves on every sprinkler? Or could I put one on the main branch for each station near the valve box? Or just one check valve on the PVC inlet to the valve box? It might still hammer, but it would be hammering on the PVC outside the house rather than the copper inside the house - correct? Just trying to avoid digging up every single sprinkler head in my complicated yard...

Proper diagnostics requires finding out what the problem is before coming up with a solution. I would suggest running a series of tests to determine exactly when the problem occurs and under what set of circumstances. You could replace a myriad of things and one of them could be the problem... or you could replace a bunch of stuff and miss the one item causing the problem.