Bath drainage

[thornton_chris]

I've recently turned my bath through 180 degrees so that the taps are at the opposite end.

This means that I had to extend the drainage pipe so that it runs the length of the bath.

I'm also putting a power shower above the bath and am worried that it won't be able to drain the water away quick enough when using the shower.

Is there anything I can do to increase drainage?

The U-bend and all drainage pipe work is new so there are no blocks. My new pipework still runs downhill but only slightly. Is it just a case of increasing the slop on the pipe or are there any plumbing tricks that I should be aware of?

Any help would be much appreciated.

Many thanks,

Chris

[Andy]

The only thing I can think of that would help, maybe, is the siphon effect, but paradoxicaly you may need a smaller bore tube to make that work ( no air can be present in the siphoning part of the drain tube. Might be difficult to make work, certainly if you're only having a shower. I imagine the big difficulty would be that the outflow rate would have to match the shower inflow rate, which might be impossible to achieve. Usually siphons are used where the outflow and inflow automatically are the same becasue the outflow rate determines the inflow!

Andy.

[Roger Mills]

You need to get as much fall as you can, and have as smooth a path as possible to the stack - for example, using sweep bends rather than elbows. Is it feasible to raise the bath a bit - maybe put it on a plinth - to get more fall?

It's not a disaster if it can't keep up with the shower flow - your feet will just get an extra wash as you shower!

[David Hansen]

On 9 Nov 2006 06:00:16 -0800 someone who may be thornton [e-mail] wrote this:-

Most unlikely. You can easily test it though. Work out how much water fills the bath and then time how long it takes to drain. You will probably find this is much faster then the shower can put water in the bath.

That's probably good.

Assuming you have single stack drainage there are maximum slopes for pipes, related to the diameter of the pipe and length of run. These maximum slopes are to prevent the trap being siphoned out.

There are also maximum lengths of run and you have just added 1.5m to the length of run.

[Roger Mills]

Are these just recommendations, or mandatory? Where are they documented?

[David Hansen]

On Thu, 9 Nov 2006 17:04:56 -0000 someone who may be "Roger Mills" wrote this:-

The latter. It is one of the things the Building Control official will check. You do get one of these to check every new connection to the drains...

Probably in a British Standard. They should also be available in various books on the subject. Personally, I have a piece of paper by one of the manufacturers which has the information.

[Phil L]

the bath will never fill up while taking a shower, try it now with both taps at full pressure and the plug out....even with very high pressure it will take an age to come even close to halfway up the bath, there's no shower on the market that can deliver that kind of volume of water

the slope on most drains is only 1:40 and even if the pipe is level it will still find the lowest point which is obvioulsy the outlet, faster than it can fill up