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?
Dunno much about underground drains...
Is the cast iron vent like a soil stack? is it against the wall?
If it is, then it seems that it's snapped off or been taken down in the past and not replaced, it should be about 2ft past the gutter, to avoid pongs coming through the bedroom windows.
If it's not then I've no idea what you're talking about, any chance of a photo or a sketch?
I remember seeing the sort of thing Dave is describing as a child living in London (Fulham - not a million miles from Dave). Definately purpose designed rather than sawn off soil pipes. Look a little like periscopes with a grill on the front.
I also assummed they were some sort of drain vent, but i've no idea how they work/ed
The message from snipped-for-privacy@o2.co.uk contains these words:
I always thought they were cellar ventilation.
Drain vents for interceptor traps. Manhole near road has what is effectively a U bend in it to isolate air movement to and from main sewer. Rodding eye (plugged) above u bend usually. Vent allows free passage of waste without air movement problems.
I have such a manhole and the vent was there but has been removed, requiring a vent pipe further back.
On Mon, 04 Sep 2006 23:11:48 +0100 someone who may be "Dave Plowman (News)" wrote this:-
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.
In the days when a trap (which regularly blocked) was fitted between the public sewer and private drains it was common to fit an air inlet (with a mica flap to prevent exit of smells) near it and a stench pipe at the head of the drain. If the building is pre-war, this may be the case.
I've got one. The grille has a flap behind it which in theory only lets air in, but in practice the flap is permanently held in the open position by 100 years worth of cobwebs. The flap looks like glass or something similar, so it might not be obvious without careful inspacetion. The vent is right next to the living room window, but it's never smelt. Neither has the manhole it vents, whenever I've had the cover off.
I suggest you open the manhole and check all is clean and well in there. You might find it's backed up, or has done so at some stage in the past and needs hosing down.
[snip instructions which I've locked]
Thanks David - I'd no idea what was down there never having looked. The one blockage we've had in 30 years was sorted via the inspection hatch at the back. I've got a shared drain with next door and they've recently got a baby - the blockage was caused by baby wipes.
Think I'll have words. ;-)
On Tue, 05 Sep 2006 23:13:53 +0100 someone who may be "Dave Plowman (News)" wrote this:-
Borrow a book on drains from the library. A good one will have diagrams of such systems. The diagrams are useful in understanding what can go wrong with them. Look for descriptions of two-pipe drainage systems as these are generally fitted with interceptor traps.
Shared drains were a common feature in ye olden days, because it reduced the costs builders had to pay by halving the number of connections to the main drain.
Baby wipes, if necessary at all, should be put in rubbish bins.
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