I wish to know if there is anything on the market similar to this: a
valve for holding in liquid until a container is near perfectly upside
down. Here is a scenario: a cap that would go on a milk jug so that
the milk only comes out when the jug is almost exactly upside down (as
opposed to tilted a little). In essence, I need a type of valve that
could work in the previous example to open only when it is almost
exaclty inverted. Otherwise, it is water tight. The valve must be
simple and cheap and keep all fluid inside the container up until the
jug is almost exactly inverted. Also, the valve must be able to be
re-used over and over with no pieces that need to be replaced each
time.
The valve (and not the method of affixing it to, or on, the jug) is my
main concern.  Please don't hesitate to ask clarifying questions.
Thanks!

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Clarification of Question by puravida77-ga on 09 Oct 2002 06:01 PDT

great questions..
It will be a five gallon jug with five gallons of water in it (plus or
minus a few onces I am sure).
The valve should allow all the water to flow out once it is perfectly
inverted. As opposed to open, but close once a certain amount of water
has left the jug (and hence left less weight on the valve). It is okay
for the valve to close if moved to an off angle once it has already
opened due to being put in the right angle (I can't foresee a user
wanting to stop the flow and remove the jug once they have started). A
spring valve could be a possibility provding it is cheap and keeps it
water tight before inverted, and can be used over and over. Might be
interesting if some type of float system could work.

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Clarification of Question by puravida77-ga on 05 Nov 2002 18:39 PST

I ended up finding the solution here: 
at the bottom left of the page.

It's called the "EZ-Load No-Splash"

http://www.waterstill.com/Water%20Crock%20Accessories.htm

Is the container always of the same volume? Is the liquid always of
the same density (eg, is it always water?) Is the initial volume of
the liquid always the same? Once the valve is open do you want the
valve to remain open irespective of the attitude (angle) of the
container or do you want the valve to close again if the container is
tilted off vertical again?

I'm thinking along the lines of a spring operated valve which once the
full weight of the liquid comes to bear, the force of the spring
keeping the valve closed is overcome and hence opens onto a latch
which keeps it open. This would only work however if you wanted an
'once open always open' type valve.

Also, what sort of size container are you thinking about - Baby
beaker? Water cooler?

I had a need for a very similiar valve when I was trying to find
effective ways to remove sediment from beer, however my valve had to
close again whenever a small deviation from vertical was made.  After
many clumsy attempts at a mechanical gravity valve I found a simple,
effective, cheap solution by building a simple mercury switch and
attaching it to cheap off the shelf electric consumer sprinkler
valves.  When vertical, the mercury comleted a circuit between two
contacts and closed a 50 cent relay connected to a 5 dollar radioshack
dc power supply that switched 20 cheap sprinkler valves to allow
sediment to flow out of inverted bottles. To stop the flow, rotate the
bottle rack with the mercury switch on the end.  Worked like a charm,
cheap, reliable, scalable, and easy to implement-no precision
machining or anything, didn't even have to tweak the switch, worked
first try (although that may have been luck).  If it turns out to be a
little too touchy it would be easy to add some capacitance to the
circuit to prevent shut offs when the water is being dumped.
- -------------------------------- -  ---  /
                                          /
+ -----\         /---------------- +  ---/
       ||------||                     valve
       ||      ||
       \|      |/
cont->  +__/\__+  <- contact
        
        switch-- ridge in middle to help mercury flatten 
        touching both contacts, if not vert, mercury balls
        up and no circuit exists.

I realized I miss read your need for a shutoff after x amount of water
has been dumped, hopefully this will calrify, I think the same idea
would work, you could easily build oscilatory circuit that shut off
valve after a certian amount of time had elapsed, chances are if the
water is being dumped into similiar containers or is subject to no
back pressure, you could obtain very accurate filling volumes with a
timed circuit, if the backpressure/flowrate is going to be variable
then a ballcock type float switch inside the big jug (look inside your
toliet:) set up in an AND circuit w/ the mercury switch could provide
the desired effect strictly based on volume rather than time.

Hi,

Try shopping for one of those nice thingamjigs they use on the booze
bottles in bars, they come in various forms, some of which might just
do what you want!

(Seems the question has expired, so I guess I'll have to go without
those 7 bucks ;)

A-)