Re: Toilet sucks in child

Date:         27 Jan 97 02:45:57 
From:         "john r." <john@guava.demon.co.uk>
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Vaccume Toilets, some horrible facts.

They are a pain in the backside, particularly for us poor people who
have to maintain them.

The 747-400 has four systems, the 767 three, each with 3 or 4 toilets.
If the loads are light a 747 may fly with one system out but never with
two missing, so a fix is a must. This is not as rare as you might think
and its very galling for us to have an otherwise fit plane dead with
such a snag.
On the Boeing system differential pressure is the driving force and
sends the 'goods' down to the holding tanks at the rear of the aircraft.
For ground and low level operation, up to 14k ft, there is a powerfull
fan system to provide suction.
When you hit the button a small squirt of water comes in at the top of
the bowl, if needed the blower cuts in and a gate valve opens for a few
seconds and woosh, the supersonic turd is on its way, or not as the case
may be.
Electronic sensors cut the toilet operation when the relevant tanks are
full.

Failure modes are many and varied, stuck open gate valves are not common
but it looks like that is what happened to the little girl, somthing can
also fall in and jam open the valve.
The pipes can block and it can take ages to locate the blockage, days in
one case recently. Often they are caused by those little pots
of facial cream from the goody bags they giveaway up front. If the upper
deck are blocked, opening the pipes on the main deck can result in
gallons of you know what all over the place.
Difusers that spread the goods around in the tank as they arrive have a
habit of breaking free and blocking the pipe to the dump valve, at the
bottom. The inlet pipe has to come off for a top dump, you hope the tank
is not too full ! Also some hero has to reach inside and try to hook up
the offending diffuser.
The dump valve release cables break, the valves freeze up, both cases
the freight floor has to come up, now we have a quick lifting panel with
slack screws but it was not this way at first.
The fans die somtimes but you can fly this way, just keep the seatbelt
signs on a bit longer untill diff pressure is strong enough.
The fan relays somtimes short and put 115v onto the tank electronic
boxes and kill two on one side, the relays are carefully hidden down a
hole but at least its a clean job.

Now you see why we hate working on them, remember there are all the
diseases of the world in those pipes. One day Boeing will get around to
fully developing the system !
We all have fund of stories about the system to relate to the squeamish,
over dinner.
Me, I do my best not to go at all when I am flying, well maybe a crafty
pee. I might get my own back.

Tootle pip !
--
  _J_O_H_N____R_E_L_P_H____________   john@guava.demon.co.uk