Water hammer from sprinkler

[JBR]

I have recently installed a sprinkler in the garden which is operated by a built-in PIR sensor and is there to deter cats from doing a whoopsie on my wife's herb garden.

When it operates there is a very audible water hammer knock, presumably because the valve closes instantaneously compared to taps, etc, which close more gradually.

I can live with the sound, but am concerned that repeated water hammer like this might damage some of the pipework or joints. Is this a possibility?

 

[Dan Robinson]

Your wife's herb garden? Not related in any way to your previous attempts at a douche?



I can only imagine the horrors you have afflicted on the water regs with this one

 

[JBR]

Perhaps I made a mistake in asking for this to be moved to the Plumbing forum.

 

[AlanE]

Try one of these on supply side of valve.

http://www.ebay.co.uk/itm/like/3015...1=ICEP3.0.0-L&ff12=67&ff13=80&ff14=108&ff19=0

 

[JBR]

Thank you Alan.
I'm grateful to find there are some helpful people on here.

What I'm most concerned about is that this water hammer might damage pipework or joints. Is that likely?

 

[AlanE]

What I'm most concerned about is that this water hammer might damage pipework or joints. Is that likely?

Depends upon how severe it is but yes possible.

Depends on your layout but a cheaper option would be to join a metre or so of 28mm pipe with blank end. Vertically so that it remains full of air.

 

[TeaTime]

What about installing a globe valve or PRV to reduce the pressure on the line?

 

[JBR]

Thanks again.

Considering the possibility of damage perhaps I should add an arrester or, as TeaTime has suggested, a pressure reducing valve. However, would either of these reduce the water pressure at the sprinkler or the outside tap to which it is attached? If so, the 'reach' of the sprinkler would be reduced and, if the pressure drops too low, it will fail to return across the full arc of coverage (I know because I tried inserting a coiled garden hose between the tap and the sprinkler, although that did stop the hammer!)

 

[AlanE]

Water hammer is the result of shutting the flow too quickly. It creates a shock wave in the water and if the pipes in the house are not securely clipped in place an audible banging results.

A pressure reducing valve might help somehow, I doubt it but it will reduce the effectiveness of the sprinkler. You can get an idea of reducing pressure by partially closing the tap or shut off valve.

Water is incompressible so if you hear several hammer blows it is because the created shock wave is bouncing backwards and forwards in the pipework of property.

A shock arrester has no effect on water flow. It is simply a 'bag of air' that can compress somewhat and adsorb any shock wave in the water. That is why I suggested you try a length of pipe. It too would provide a cushion of air to absorb the shock way.

Only other way would be to slow the action of the valve you are using.

 

[JBR]

Thanks Alan.

I think that the (long) coiled hose was probably acting as a PRV and, of course, that did reduce the pressure.

The noise I hear is just a single knock when the valve closes and, unfortunately, the closure of the valve cannot be slowed as it is either open or closed operated by an electro-magnet and I wouldn't want to start fiddling with it anyway in case I made a mess of it.

No, the best option, I think, is to insert a shock arrester as you suggested. You said 'on the supply side of the valve' which I assume would be somewhere along the pipework leading to the outdoor tap. The nearest I could get to would be under the sink which is about 12 feet from the tap and probably a further 30 or 40 feet from the valve in the sprinkler. Do you think that would be OK?

 

[JBR]

It has occurred to me that it would be easier and perhaps more effective to attach a shock arrester directly to the sprinkler. As you can see from this picture of a similar item to the one I have:

View media item 93332
there is a second attachment point for a hose extension (on the left) where I think the arrester could be fitted. It's just a matter of finding the correct adaptor(s).

 

[AlanE]

Try connecting a length of hose to the second connector and blanking off the far end of it. I might just work and be a cheap fix. Could even use a small fizzy drink bottle at end to blank off hose. That would enable you to use a shorter length of hose but as said it must contain air only.

Come off the connector and loop the second hose upwards. Can go in a circle, not important. What is important is that this extra length of hose contains just air, it must remain free of water or it will cease to work.

 

[JBR]

Thanks. That's a good idea, although I might pass on the pop bottle as my wife would kill me.

 

[JBR]

I thought about getting one of these:

http://www.amazon.co.uk/Arrester-Pr...sbs_diy_1?ie=UTF8&refRID=0085FS5W0PE99ACMG9MA

However, although the main culprit causing water hammer is the garden cat repeller, there is also a water hammer when the washing machine is running (although much less loud) and also when turning off a quarter-turn tap on the sink (although I've asked my wife to turn it off more slowly!).
Could anyone advise me the best location for this shock arrester to help with all causes of water hammer?

 

[TeaTime]

Have you checked what your incoming water pressure?
Perhaps that can be reduced if it's very high.