Syphon with a built in overflow???

[gcol]

I just bought one of these http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=100996&ts=22667&id=44047 cause it mentioned it had an internal overflow. I thought about removing the old overflow pipe from the cistern. However, am I reading it right? I can't see where or how water rising in the cistern will get to a point where it starts coming through the syphon and into the pan. Do these syphons really have a built in overflow? And if so, how the blazes do they work?
Cheers.

 

[fitz1]

yes they work. they tend to have a hole above natural water level.

 

[JohnD]

Are you sure that's the right one? It looks like an ordinary syphon and the description does not mention it. Perhaps the description was wrong?

This sort has an internal overflow:

and
flapper - my favourite

 

[gcol]

I can't see a hole anywhere but the screwfix description mentions an "internal overflow".

 

[bster]

I think the water travels within the syphon not from outside, so when the water level rises above normal it simply spills over the syphons internal weir and into the pan.

 

[chr15]

You're dead right bster,the only thing that makes it an internal overflow is the shortness of the main column so when the water rises it simply spills over the top of the weir and back down into the pan.

 

[bster]

yeah another thlng right

and a customer thought i was the company's heating expert today!

so i feel good for once!

 

[gcol]

Ah, nice one guys - I feel better about fitting it now.

 

[Softus]

Do these syphons really have a built in overflow?

All syphons have a built-in overflow, but it depends on the height of the cistern, and the handle hole (and any cosmetically blanked holes) whether the syphon will internally overflow before the level reaches another outlet.

 

[gcol]

Hmmm now you have me worried Softus.

 

[gcol]

So just to clarify, this syphon which "facilitates internal overflow" will not allow water tp pass through it in an overflow situation until the water level rises above the top of the bend in the syphon (where the blue cap is)? Is that right? If so, I'm gonna need a different syphon.

 

[chr15]

Thats correct-the water level on the outside of the syphon is the water level on the inside of the syphon-usually an internal one-as they are called,has got a much shorter column so therefore would overflow back into the pan before reaching the floatvalve or handle hole. It looks the same as a regular syphon but is just a lot shorter and stubby looking,as Softus mentioned earlier,all the syphons are internal overflow it just depends on where the water within it is allowed to rise up to.Hope this helps. Chris

 

[gcol]

Yes it does, thanks.
So are those flapper units any good? Does the flap/bung bit not drop down mid flush?

 

[bab]

Just wondering why you require an internal over flow ? The flap type will be a better option as the only type of true syphon that will overflow internally on a standard cistern is a 6ltr flush wich is a reduced design flush 4 your pan. it will be either 7.5 or 9 ltr flush. new 6 ltr pans have a reduced water content allowing a reduced flush content to remove solids. Fitting a 6 ltr syphon to a w/c designed to flush 9 or 7.5 can cause solids to remain. if the flap type is too short u can extend the overflow up to the existing overflow height, U also need a very good seal on your donnut washer with a flap type.

 

[JohnD]

Yes it does, thanks.
So are those flapper units any good? Does the flap/bung bit not drop down mid flush?

1) Yes

2) No, it floats, so it only drops down when (almost) all the water is gone. When the cistern refills on a closed flapper, the water pressure holds it down and pushing against its seal.