Dishwasher waste fitted correctly?

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Hi experts,

What happens if a dishwasher is fitted into a waste pipe with nowhere for air to get in?

My plumber removed a sink but left the dishwasher draining into the sink waste, which looks something like this:
http://www.diy.com/diy/jsp/bq/nav.j...cificationsSpecificProductType=other_fittings

With the sink in place, the dishwasher waste could breathe out the plughole in the sink, but now there is a cap in place of the sink and I'm wondering if I'll have problems with siphoning and air locks.

Any advice appreciated.

Thanks,
Chris
 
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You won't have any problems as the water is pumped away and there will be a vent somewhere along the drain line.

Andy
 
Great, thanks Andy. Dishwasher is running now, glad to hear there shouldn't be any problems.

Cheers,
Chris
 
You won't have any problems as the water is pumped away and there will be a vent somewhere along the drain line.

Andy

Andy - this is the new setup I've got:

dishwasher-1.jpg


When the washing machine drains it empties into the sink. It only gets about an inch high and it drains away quite quickly after the pump stops. The waste hose from the washing machine is attached to a spigot on the sink waste and rises up above the level of the u-bend before going back down to the washing machine so I'm assuming nothing drains back from the sink.

The only part that breathes is the sink - could a lack of air in the system slow it up or should the communal soil stack be enough (I'm in a flat, second floor of three)?

Thanks for your input!

Cheers,
Chris
 
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If washing machine is filling the sink then the water isn't getting away quickly enough. Either badly fitted pipework or possibly partial blockage in the pipes. Does the dishwasher waste go straight into the stack or does sink waste join it before it gets to the stack?
 
If washing machine is filling the sink then the water isn't getting away quickly enough. Either badly fitted pipework or possibly partial blockage in the pipes. Does the dishwasher waste go straight into the stack or does sink waste join it before it gets to the stack?

I don't actually know. The stack is in the corner of the kitchen behind the kitchen units and both sink and dishwasher wastes disappear behind the units before they get to the stack.
 
Afraid you may have to either live with it or do some further investigation behind the cupboards..... ;) Possible it may reduce to a 32mm pipe prior to reaching the stack, 32mm simply cannot cope with washing machine emptying.
 
Afraid you may have to either live with it or do some further investigation behind the cupboards..... ;) Possible it may reduce to a 32mm pipe prior to reaching the stack, 32mm simply cannot cope with washing machine emptying.

The washing machine waste was hooked into a 32mm waste originally, as in the top of it was open and the hose just dangled down into it, if you know what I mean. Now the sink shares this 32mm waste which admittedly is probably too small but if the washing machine managed to discharge into it before then why is it having trouble now? I can live with it, and putting the plug in the sink prevents the discharge, I just worried that there was something more seriously wrong.
 
Possible someone had made a 32mm standpipe, (not aware of a 'ready made' version in 32mm, for the simple reason 32mm cant cope with a W/M discharge), and I assume the discharge would have started to fill the vertical section before the head of water increased the pressure and forced the water to flow in the right direction. Maybe more luck than judgement it didnt flood over the top. :eek:

Now the washing machine is discharging into the sink trap it the water will take the path of least resistance, in this case coming up into the sink as opposed to draining away immediately. It may simply be there is now more resistance in the waste due to an elbow being fitted where there wasnt before that is now restricting the outflow from the sink.
 
Thanks Hugh, this sounds like a reasonable explanation of what's happening. I was also surprised that the sink/dishwasher had 45mm but the washing machine had 32mm. I guess because there are both a sink and a dishwasher, compared to just a washing machine. It's also possible there was some DIY done on the plumbing before I bought the flat. The plumbing certainly wasn't "tidy" when I inherited it :)

In the new install, the plumber has installed a flexible hose (the extendable bendable type) from the sink trap to the 32mm waste pipe. I'm assuming this will create additional resistance for the water.

My thoughts were to go back to a standpipe configuration but from your comments I'm thinking this will be a bad idea!
 
I (personally) dont like the flexi waste, too many ridges and troughs for crud to collect in. :( How much pipework is done in 40mm (1 1/2")? For these appliances it really should be 40mm (if not 50mm for part of the way).
 
dishwasher-1.jpg


Here, everything from the dishwasher to the stack is 40mm, everything else is 32mm.
 
In that case then i'd upgrade the rest to 40mm. Cant understand why your plumber has run part in 32mm, especially with a washing machine connected for the very reasons you are now experiencing.... Get rid of that flexi at the same time! ;)
 
The 32mm pipe has been in place since the flat was built and the washing machine has always discharged into it. It mostly runs behind the cabinets in the cupboard, so it's not easy to upgrade it.

As to why this was installed this way to begin with, I suspect the sink/dishwasher were (at some point before I bought the flat) swapped with the washing machine, and I have only just swapped the sink back, which would explain why the pipe diameters are all wrong.
 

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