My weird sink drain

Improper vent installation.



"AES" wrote in message
...
| This is totally OT for this group -- except the group
contains a lot of
| obviously clever people who are professionally interested
in aerodynamic
| and fluid flows and pressures, pipes, valves, and the
like, and maybe
| someone will be entertained by the following odd bathroom
sink behavior.
|
| Our newly remodeled bathroom has a circular glass
above-counter sink
| like a hemispherical glass salad bowl, about 18" in
diameter at the top
| and 7" deep, with a push down-pop up drain plug in the
bottom center,
| and a pretty high capacity faucet above it. Standard
elbow fitting and
| drain pipe going into the wall underneath the sink and
counter top.
|
| With the drain open, turn the faucet on full force: water
gets dumped
| into the sink considerable faster than it can drain out
and the water
| level in the sink rises rapidly up to the rim, on the
verge of
| overflowing, in 20 or 30 seconds.
|
| At the last second turn the faucet part way off -- down to
roughly 50%
| of full flow, more or less -- then trim the flow until
inflow rate just
| equals outflow, so the water level stays just 1/4 inch or
so below the
| rim. Then leave it in this steady-state condition, and
wait.
|
| For approximately *eight minutes* (by the watch) the
resulting situation
| remains perfectly stable, with water level hovering just
below the
| overflow point. Then, all of sudden, water level starts
dropping.
|
| Turn faucet back up to full flow. Water level continues
dropping, keeps
| dropping faster in fact, until sink is essentially empty,
and the full
| force input that initially caused the sink to fill now
roars down the
| drain with only 1/2' or so of water swirling around the
drain in the
| bottom. This continues as long as I want to watch.
|
| This doesn't seem to result from just blowing some
temporary clog out of
| the drain: I've repeated it three times, several hours
apart, with
| essentially identical behavior.
|
| I'm at a loss to explain how it happens, except to
hypothesize that
| maybe there's some point underground and quite a ways
further down the
| drain where the drain pipe has a long slow rise, then a
drop, and in
| some way the initial slower flow has to fill the rising
section until a
| siphon action gets going over the top?
|
| That doesn't really sound persuasive, however. Anyone
have any other
| ideas?