Sorry Peggie, I seem to have lost you somewhere along the line.
Two topics, duck bill valves and o-rings. Very different things, indeed.
A "duck bill valve" is a type of valve like a "ball valve", "globe valve",
"check valve", etc. I'm not personally familiar with "joker valves" but my
comments regarding probable causes of leaks when the attaching screws are
"over tightened" is still a viable probability. At least as I visualize a
joker valve.
My comments regarding o-ring was in response to a comment of yours that
either said or implied that over tightening screws on an o-ring seal would
cause leakage. Obviously one should never "over tighten" any screws but the
probable failure in an o-ring seal situation is stripped or broken screws
and not leakage. An o-ring seal will be designed to have the flanges fully
closed when assembled.
BF


"Peggie Hall" wrote in message
news
BF wrote:
I've never seen a joker valve (lots of duck bills though).

Hmmmm....we may be talking about the same part, but Jabsco,
Wilcox-Crittenden, Groco and Jabsco all call it a joker valve in their
exploded parts views. The only mfr who calls 'em duckbills is SeaLand.


From my
visualization of your description what is probably happening when you
over-tighten the screws is not puckering of the sealing surface...

Yes, it is a puckering of single piece of rubber (the flange on the
joker valve) between the flange on the on discharge fitting and the pump
body. If over-tightened screws are backed out a bit within a short
period of time, the rubber regains its shape and seals the leak...but if
the screws remain too tight long enough, they deform the rubber
permanently...the only fix is a new joker valve.

but
deformation of the flanges between the screw points causing a reduction
in
pressure between the two flange surfaces.

Huh????

O-rings seals, when properly designed and manufactured should be
assembled
with their flanges in contact with each other, ie bottomed out.
Obviously
referring to face seals here and not radial o-ring seals.

I think you just WAY over-complicated something that's really very
simple... All we're talking about here is two pieces of hardware
(usually hard PVC, but can be bronze on older toilets) with a flat piece
of rubber between 'em, held together by 2 or 4 screws.

You can see the parts in question in the exploded drawing of the Groco
Headmate he
http://www.groco.net/images/toilets/...-SM/HF-pg2.jpg (click
on the drawing to enlarge it to a readable size)... parts #14 (discharge
fitting connector) and 4 (pump body) with part #16 (joker valve) between
'em). It's the same on all toilets, and you can see by also going to
the drawing for the Raritan PH II he
http://www.raritaneng.com/pdf_files/...Ephiiv0303.pdf

--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"

http://www.seaworthy.com/store/custo...0&cat=6&page=1

http://shop.sailboatowners.com/books...ku=90&cat=1304