"Set Square" wrote in message
...
In an earlier contribution to this discussion,
andrewpreece wrote:

I'm not sure about the meaning of a test I did. First, let me explain
that my grey/rain water
all empties into a gully on the side of my house. I think it empties
into a salt-glazed sewer pipe.
The sewer pipe is buried under a concrete ledge running along the
side of my house.

After about 8 feet horizontally a soil pipe from the upstairs loo
enters the same concrete ledge, and joins the same sewer pipe, i.e.
my sewage and rainwater all empty into the same pipe. Just before the
sewer pipe reaches the road there is an inspection chamber, and
whilst looking in there for a completely separate reason, I rashly
decided to do a leak test.

I bunged up the sewer pipe in the inspection pit, then went to the
gully and ran water into it until it
filled up the ceramic pipe draining the gully to the lip. The water
level then dropped two inches in some 40 seconds or so, then dropped
much more slowly. I repeated the test and listened for what I could
hear along the route of the sewer pipe, and distinctly heard water
gurging for 40 seconds where the soil pipe enters the concrete ledge.

Sorry to bang on in such detail, but my question is, would you folks
expect the ( unseen ) join between a soil pipe and a sewer pipe to be
airtight, or is it arranged so that flowing water coming down the
soil pipe negotiates the join ok, but standing water being pushed
back up a few inches
above that join will leak out?

Do I have a problem, or am I meddling with stuff I don't understand?
:-)

Andy.


Is it possible that you trapped some air in the pipe - which subsequently
gurgled out, causing the water level to fall? If so, you may not have a
leak
at all.

Although I'm not by any means an expert, my impression is that leak tests
are normally performed by bunging up *both* ends of a pipe and then
pressurising it with air - and measuring the pressure drop over a
specified
time.
--
Cheers,
Set Square

It is possible some air was trapped I suppose, but the sound I heard was
trickling,
definitely water on the go. At any rate, no air would have been trapped in
the soil pipe,
as of course it opens to the air at the eaves via the stench pipe.

Also, I repeated the test three times, with identical trickling noises, and
a fall of the free
surface of the water by about 2" over about 40 seconds, whereupon it slowed
to less
than an inch over 5 minutes.

I cannot perform an air pressure test without much ado, but if you say that
a sewer pipe
should be able to pass an air leak ( when stopped up at the ends ) then I
reckon I've
definitely got a problem. I wasn't sure if a metal soil pipe-to-glazed sewer
pipe connection
had to be air tight or merely be able to take a vertical fall of water
without leaking ( in the
same way a roof is waterproof but not watertight ).

thanks,

Andy.