On Mon, 04 Sep 2006 23:11:48 +0100 someone who may be "Dave Plowman
(News)" wrote this:-
There's a cast iron drain vent on the front of my house - just above an
inspection cover - which has started to pong a bit sometimes. It's a sort
of horizontal grill on top of the pipe about 3 ft above ground level. I
assume there should be some form of valve in it since there's no water
flow to keep a u- bend full? And this has failed?
As has been said, this is almost certainly a vent for the
interceptor trap that is below the inspection cover. I take it your
house was built before say the late 1950s.
There should be a flap behind the grille to stop air being pushed
out of the grille but allow air to be drawn in. However these never
lasted very long and if still present has probably rusted up in a
semi-open position.
The bad news is that if the vent has started to pong then the reason
for the pong is almost certainly a blocked interceptor trap. Heavy
material in the bottom of the manhole will be rotting slowly and
giving off fumes, lighter material will be flowing through the
partially blocked manhole and out through the rodding eye above the
interceptor trap.
To sort this out:
1) remove the inspection cover. You should find a partly full
manhole.
2) see if you can see the chain that should be holding the stopper
for the rodding eye. This chain should be fixed to the top of the
wall of the chamber above the rodding eye.
3) pull the chain up. With luck the stopper will come up and the
manhole empty. If it doesn't then either the chain is not connected
to the stopper, which is now blocking the interceptor trap, or there
is no stopper.
4) check for the stopper with the aid of a probe. Your hand is best
for this. If you find it lift it up and listen to the sound of the
chamber emptying, otherwise there isn't one.
5) if there isn't a stopper rod through the rodding eye, which
should be just above water level, to the main sewer, just to clear
anything that may be partly blocking this run.
6) put a plunger on the end of a rod and feel for the channel at the
bottom of the manhole. This channel runs from where the pipe comes
in down to mouth of the interceptor trap, which is at/near the
outlet side.
7) when the plunger is in the interceptor trap plunge sharply a
couple of times. With luck there will be a gurgle and the level of
liquid in the manhole will go down.
8) clean the rods and manhole.
9) clean yourself.
10) have a few drinks.
After a suitable amount of relaxation, if you have the stopper
fasten it with a bit of nylon rope so that it cannot fall into the
interceptor trap and put it back in the rodding eye. If you don't
have the stopper then cement in something like a piece of slate into
the rodding eye. This can be smashed if necessary to rod through.
If you wish to keep the relic of a not too bright drainage system
then it might be worth trying to get the flap working or replace it.
The idea was that air would flow in through the flap and out of the
top of the soil pipe, thus keeping the air in your drains fresh.
Some people remove the air vents, but this should only really be
done after the interceptor trap is removed. An alternative is to
leave the rodding eye open, so that fresh air from the sewer flows
through your soil pipe, as it would do in a modern drainage system.
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54