Water hammer (new washer-dryer)

The new washer-dryer causes fairly loud water hammer every few minutes when drying (I haven't any noticed noise when washing, but it probably only cuts on and off a couple of times over the whole programme).
I've seen water hammer suppressors that fit between the appliance hose & the connector:
<https://www.screwfix.com/p/sioux-chief-dw660-h-water-hammer-arrestor-bsp-connection/9813r
but I don't have room for one of those under the kitchen sink, especially since I think it has to be installed pointing up.
There's also the freestanding kind:
<https://www.screwfix.com/p/sioux-chief-dw660-2j-water-hammer-arrestor-bsp/1492r
which says "single-appliance", but I would have room to fit that to the cold water supply running through the crawl space under the dining room to the kitchen, & only one appliance is causing hammer. That one says 1/2" BSP, so I guess the installation method is to cut a gap of the right size into the water pipe & fit a tee with a 1/2" BSP pointing up --- is that right?
I'm also thinking of trying some more "improvised" measures first, such as wrapping the pipe in rubber (old bike inner tube) & clamping around that to a joist --- is that realistically likely to make a difference? (The pipes below floor level are already covered with insulation & expanding foam.)
Thanks.
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Could one of your appliance hoses be a little too elastic?
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On 25/03/2020 15:15:44, John wrote:

I would have thought quite the opposite.
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No - a soft pipe acts as a rebound.. I notice at home if I leave my garden gose attached - but turned off at the nozzle, hammer is very much a problem.
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On 2020-03-26, John wrote:

I checked the hose & it's the least elastic appliance hose I've ever seen. Anyway, I looked at the in-line water hammer arrestor again & the orientation doesn't seem to matter (there's a piston in the leg) so I've ordered one to try.
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It can be any hose.
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wrote:

AIUI the piston separates the water from the air 'cushion'. A diaphragm does much the same thing. Again AIUI, if the two aren't separated, the air in the 'cushion' slowly dissolves in the water and eventually disappears, allowing the hammer to return.
On that basis, I would think that anyone with an unvented water system and expansion vessel would be protected against hammer.
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Chris

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Wee would there be hammer when its drying, surely you might expect it when wetting!
Brian
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Brian Gaff wrote:

condenser dryer
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On 2020-03-25, Andy Burns wrote:

Yes. (I probably should have clarified that to start with, but all the washer-dryers that I've seen use condensers to the washer drain rather than a big air vent.)
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Does the washer drain go into a standpipe or direct into the waste system? The former is usually more satisfactory.
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Is the main advantage of condenser driers that they don't need to vent a lot of hot air to the outside, or is there any other advantage? I find that they do not do such a good job: the clothes are often very hot but still nowhere near dry at the end of a long drying cycle, and they are also very creased.
The best driers I used were laundrette-style ones at my university hall of residence, which used gas burners rather than electric elements to heat the air, and left clothes dry and yet not creased.
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I suspect that’s a washer/dryer issue rather than a condenser dryer issue. Tumble dryer drums are normally a lot larger than washing machine drums to allow plenty of air to circulate. Not possible with a washer dryer so you can’t effectively dry a full washer load.

More to do with the size of the drum and air flow than the heat source.
Tim
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The drums are smaller than most ordinary tumble driers I am familiar with, so you cannot dry as much washing at a time - you really do have to avoid over-filling them. I find my condenser drier useful (we have no space for a separate one), but mainly to finish off drying laundry that has mostly-dried outside or in a room with a running dehumidifier. But it does work fine on small-enough loads.
#Paul
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On 2020-03-26, Roger Hayter wrote:

It used to go into a standpipe. Then we had the kitchen renovated & the same washer-dryer went into a combined sink trap & waste manifold under the sink. Then we replaced the washer-dryer (still going into the combined waste) & the water hammer started. But I don't see what the output of the appliance has to do with water hammer in the supply pipes.
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Is the "Condenser" water cooled?
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I was caught out by that. We'd just moved into a new house and the house already had a washing machine (without tumble drier). We were planning to do some building work in the room that had the washing machine, so we got the removal men to put our own washer/drier in the garage near a water supply and drain, so we could use it as a drier or as a second washing machine in the meantime.
The first time I came to use it, I plugged it into the mains but didn't connect it to the water supply because I was only going to use it as a tumble drier. And it faffed around for ages, lazily tumbling the clothes every few seconds but without ever getting to the point where blower fan started running. After about half an hour, it displayed an error code which was not one of the codes that was listed in the manual (don't you just *love* undocumented error codes).
Then it dawned on me: being a condensing drier it probably needed a water supply even when working as a drier. As soon as I connected the hose and turned it on, the drier worked as normal.
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Worth checking to see if your cold water system might have an air filled dead leg somewhere.
We fitted a surestop valve once but every time it was actuated it caused an almighty bang through the pipework. I was quite worried that it would push apart pipe fittings such was its strength.
Turned out we had a redundant cold feed in the loft to an old shower that must have the accumulated air. Removing it cured the hammer.
Tim
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On 2020-03-26, Tim+ wrote:

...

That's interesting. There is a dead leg under the kitchen floor (the appliances used to be on the other side), but the old washer-dryer didn't cause water hammer after the renovation. But from what I've read on the www, adding a pipe with air in it is supposed to be a way to *reduce* water hammer (the air cushion absorbs the sudden pressure changes).
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It can work both ways depending on resonance I believe. Certainly the dead leg was the cause of our troubles.
Tim
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