Internal cistern overflow to drain

[Tim S]

Hi,

One more logistical wibble:

Have an islanded bathroom - no external walls. Obviously bog cistern needs an overflow.

I've seen, in commercial buildings, enclosed overflows to drains with a little window in front, basically:

3x4" window;

Big pipe (or funnel) in base of enclosed space

22mm pipe in the top, end hanging over funnel.

Thus the overflow goes straight down a drain pipe, but there is a visual guide if the overflow is in use.

Anyone know where to get one?

I guess I could make one to, with a bit of clear tube inserted into 40mm waste pipe with a 22mm overflow into the top.

But I'm curious about the ones I've seen...

[Steve Walker]

Or just change the mechanism to one with a much neater internal overflow. Any overflow goes into the toilet pan and drains away, the continuous flow is visible in the pan.

SteveW

[The Medway Handyman]

Oh no it doesn't!

All the new bog siphons I've seen have an internal overflow e.g. if the fill valve fails, water overflows into the WC pan.

Usually reported by the punter as 'toilet won't stop flushing', I can either tell them 'adjust the fill valve to reduce the cistern level' or 'I can sort that for you, it will be £30'.

:-)

[Heliotrope Smith]

The clear tundish and flush pipe clamp can be got from most plumbers merchants.

Far better surely to fit a siphon with internal overflow.

[Tim S]

Heliotrope Smith coughed up some electrons that declared:

"tundish" - the magic word. Never heard it before, but now it makes sense, finding many examples on the web. I reckon what I saw was a white tundish, that simply had a window set into the cistern enclosure fascia, so more custom, than an actual part (the actual part being inside).

Thanks.

Probably... For some reason I have never questioned the possibility that these existed (sheltered life )

But, yes, I shall ask in the shop...

Cheers

Tim

[John Rumm]

You get them any place you need an air break as a well - like on pressure release valves on unvented hot water cylinders.

Most modern designs that use a flap valve rather than a traditional syphon are like this now...

[ARWadsworth]

You would have loved the overflow I saw at work last week. It went staight down to the pan and was hammered flat to allow the toilet seat to be lowered.

Adam

[Tim S]

ARWadsworth coughed up some electrons that declared:

I've seen that too...

[The Medway Handyman]

...and me! Seems common in pubs.

[The Medway Handyman]

Spawn of the Devil, no good will ever come of them...

Syphons are simple & uncomplicated, there was no need to 'improve' them.

I don't think I've come across a syphon recently that *didn't* have an internal overflow.

Or is is Siphon?

[Owain]

I've seen one of them too.

Owain

[Matty F]

OK, explain the essential parts of a syphon cistern and exactly how they work!

[YAPH]

It's simply a matter of geometry. If the syphon valve is short enough that the top of the inverted 'U' is below the level at which water leaks out of the cistern by other orifices (why do they have that dip in the rim of the back wall of the cistern?!) then it will act as an internal overflow. You can readily get (IIRC) 8" and 9.5" syphons, and I've seen shorter.

[<me9]

I've assumed it's to let air in when you flush.

With internal overflows the air can't enter via the overflow during a flush.

[The Medway Handyman]

Simplicity itself.

A siphon is an inverted 'U' one end of which connects to the WC pan, t'other end is open & about 10mm above the cistern base. Obviously the water level inside & outside the siphon is the same.

In the base of this end is a plastic diaphram on a grid acting as a flap valve. When you flush the bog the diaphram lifts water over the 'U' bend and starts the siphon which continues until its pulled almost all the water out of the cistern & air breaks the siphon.

The diaphram is then pushed down by a spring allowing water back into the siphon, ready to start again.

Essential parts; 1 x plastic diaphram, 1 x spring, 1 x linkage to flush handle. Complete list of possible faults; linkage comes off, diaphram splits.

Nice picky.

Why would you want to 'improve' something that simple?

[Dave Liquorice]

Spring? I thought i was just weight of the frame/diaphragm, link and arm= that just pushed it down. Mind you I've never had need to take one apart= as they are so reliable so there could be a spring in there but I doubt =

it.

Beacuse compared to the drop flap type they are complicated to make/assemble and use more materials? Why spend =A35 on manufacture when= you could spend =A33 and charge the same for the product... The fact the dro= p flap type are less reliable and lead to wasted water isn't relevant.

[PeterC]

Or, in mine, the diaphragm stiffened and didn't really 'flap'.

[Heliotrope Smith]

Spring? I thought i was just weight of the frame/diaphragm, link and arm that just pushed it down. Mind you I've never had need to take one apart as they are so reliable so there could be a spring in there but I doubt it.

Very common for modern plastic siphons to be spring assisted. Still find the occaisional older types with lead weights to push the diaphragm down.

Beacuse compared to the drop flap type they are complicated to make/assemble and use more materials? Why spend £5 on manufacture when you could spend £3 and charge the same for the product... The fact the drop flap type are less reliable and lead to wasted water isn't relevant.

[YAPH]

Bring back the bell syphon, I say.

Seriously: no sheets of polythene in inaccessible places to pack up, no washers to let by when they cease being 101% perfect. Made of modern materials (rather than cast iron!) and with perhaps a bit of smarts to make them easier to flush and perhaps some sort of dual-flush arrangement and I reckon they'd be the nearest to the ideal flush valve you could get.

[The Medway Handyman]

There has been a spring in the last two dozen or so I've changed.

Drop flap types have chains, floats to ensure they close & are a right PITA to adjust properly. Much more complicated than a siphon.