On Thu, 15 Oct 2009 06:43:37 -0700 (PDT), Andy Dingley wrote:

On 15 Oct, 14:08, Tim W wrote:

The only question I have is will they really cope with a wedged lump of bog
paper and 4l of water travelling down the pipe after a bog blockage as
that's quite a lot of suction and air volume?

The HepVO will open during the flush with a mighty rushing wind
through the basin, then close afterwards. HepVOs make excellent AAVs.

Sadly they make poor waste traps. In particular, any sort of foreign
bodies down the basin waste will cause problems. Things that a bottle
trap would happily flush through, or hold onto without problem, will
cause a HepVO to start jamming open. There's no "dead space" in a
HepVO, as there is with a bottle trap, so the smallest particles will
tend to start accumulating blockage-builders - in particular,
washbasin hair.

Personally I'd be very reluctant to use HepVOs again.

The sink on which I fitted one has all sorts of junk down it and hasn't had
a problem for ~7 years, although I can see that something stuck in the trap
would leave it 'open'.
Bottle traps etc. syphon and can lose water due to the wind causing
oscillations and evaporation; also string/fabric/hair can syphon off water
by capillary action.

On balance, I'd rather have HepVO, especially for low throughputs where a
trap might hold muck that putrifies.
Disadvantage: any object accidentally dropped in (earing, false tooth)
ain't gonna be there!
--
Peter.
The head of a pin will hold more angels if
it's been flattened with an angel-grinder.