elmo said...

The use of O'rings is not flawed.

The use of the wrong sized ones is.

Most Orings used are 1.25mm - 1.5mm cross section do not cover the thread entry properly.

It's not a tough issue to resolve.

have to disagree...compressing an o ring between 2 flat surfaces (one of which is spinning) is not the right application or use of an o ring...although it works in a fashion

snides8 said...

elmo said...

The use of O'rings is not flawed.

The use of the wrong sized ones is.

Most Orings used are 1.25mm - 1.5mm cross section do not cover the thread entry properly.

It's not a tough issue to resolve.

have to disagree...compressing an o ring between 2 flat surfaces (one of which is spinning) is not the right application or use of an o ring...although it works in a fashion

Speaking as a "Gasket" manufacturer using a flat gasket on a rotating surface is none to good either in fact with the introduction of sand it is worse.

The "O"ring as you say is not ideal but it does have the benefits of point loading which can give a better seal.

The big problem is that the sizes of the "O"rings generally used are to small and that they barely cover the groove which is the start of the thread (no the top of the hole is not a smooth faces some people may believe).

By increasing the OD of the oring, you get a larger contact area, a correctly chosen "O"ring cross section will also allow the "O"ring to seal on the outside of the hole as well as the bottom face of the hole. I had to do this after I had a vent hole redone with a Helicoil (metal thread repacement) which requires a bigger hole to be made, since using the larger "O"rings I get a definitive pressure change (hissing air) when I open the vent after a session.

Sand in the hole can still allow (within reason) the plug to seal, but will be detrimental to the life of the seal.

Plug "O"rings and gaskets should be checked and replaced regularly, as Steve said they rotating action of the plug is not what a "O"ring is originally designed for and IT WILL WEAR.
If you are a gorilla who thinks the bung should be tightened to such a load that it pokes out the bottom of the board then yours should be checked and replaced more frequently. Sand will also wear away at the "O"ring.

Do not blame the manufacturers of your board because you don't check your kit properly.

hello mr evil,
i am allways suss of water leaks, as a plumber i see a few of them, especially on worn o rings,! as a back up i allways keep some blutack with the vent screws (for my old fashioned bung boards) which i squeeze over the top of the vent once its screwed in place,as an added barrier to water.

jp747 said...

....am as forgetfull as a drunk if excited..i've done stupid things like going zipping along the water only to forget the fin cover was still attached(my mate did this one stunt too) and the usual something's missing-where's my harness?!?but i should start doing that by taping the vent with a colored tape once in a while to remind me to close...

he he... I've done all those once or twice
"I've done all the dumb things". I now religiously double check the vent before going on the water and I haven't missed it for years.

snides8 said...

snides8 said...
[
the fact remains if you, for example, screw your bung in to the board when the temperature is 20deg and you leave it in and the temp goes up to 40 then the volume of air within the board will double thus creating a lot of expansion force inside the board.

ok nobody picked up on it!
note the use of the word VOLUME no mention of the word 'pressure' see
'charles law'......

well I thought Nebs picked up on it when he posted this.

And if the temperature ever hits 0 then you get a division by zero error and the universe explodes... let alone negative temperatures

The real physics is as follows:

PV = nRT (en.wikipedia.org/wiki/Ideal_gas_law)
Pressure x volume = number of gas molecules x Some constant x temperature

Temperature is in kelvin.

So the difference in pressure between 20 degrees C and 40 degrees C is around 6.4%, assuming your board doesn't expand due to temperature (which it will, so the difference in pressure will be less)

Question. On it seems a normal !? 40 degree Day in Perth, Do you store your Board, Strap so Up, to let moisture evaporate,(which may have accumulated) or strap side down? And could this method if used, help dry the board out?

ps.after i sail i bring board home wash down.let to dry over night and then remove plug.and store plug in your favourite place. Before i sail i inspect plug hole for sand etc. i then wet plug washer with a bit of spit! which allows O ring to bed better when tightening not to tight.

any thoughts?

OK Snides, I've googled Charles law, and re-read your post.

I guess I assumed a couple of things, which was probably silly of me.

You are perfectly correct if:
You live in a really really cold pocket of WA with a temperature of 20 kelvin. I'm not sure how you breathe at that temperature, because nitrogen isn't a gas anymore.
And I'm dying to see your board that somehow keeps a constant pressure by varying its volume. Maybe it's a windglider?

Sorry for jumping to conclusions before, I really should be a bit more careful.

evlPanda said...

Yes, you must have a mantra before you hit the water. Bung: check, harness: check, car keys: check.

Question: Why not a one way valve instead of the bung?

that'll be a good idea self-regulating valve, funny how you blokes call a vent plug a bung wow nebs and decrep did you ever wanna be professor of sciences in your past life? concise down to the last letter explanations

555 said...

A self regulating valve eh... maybe something made out of goretex that lets air through but not water??

Carbonart fit them as standard equipment.

Never bother with a vent screw, or bung ever again. Plus, you can't ever forget to do it up if you never have to undo it.

Price is the issue.. it's cheaper to fit a screw than a goretex vent.

true regarding price..better a dry board than a waterlogged one if ever vent's forgotten kinda not worth the risk in my forgetfull doings

My o-ring is water tight although i occasionaly hear air vigorously escaping

No. On second thoughts, I just got a mental picture of sailing along and looking down and seeing stribos sphincter winking back at me from where the vent plug should be.
Not a pretty sight.
Better try something else.

lol

hardpole said...

The idea of a one way valve (bike valve etc...) is no good becase I imagine sometimes the air goes out (as it heats) and then it needs to go back in (when it cools overnight)

>>>>>

So why does it need to go back in ?????????
A slight +ve air pressure on the outside of the board, shouldn't do any harm, after all it's designed to handle the riders weight squashing it against the water surface. A much greater force.

elmo said...

For the same reason it needs to go out. remember Ye olde Prof Jullius Sumner-Miller experiments.

Admittedly the shape of the board makes it more resistant to compression than expansion

Absolute rubbish, it needs to go out so the board doesn't blow up like a balloon, the tensile strength of styrofoam is almost zero.
All the internal air will concentrate at any weak point.
The stiffness of the sandwich skin isn't a lot of help here, especially on the flat area of the bottom. It only has to release a few mm at first, but once a bit of air is between the bottom skin and the core, sailing action will "pump" that air into the adjacent skin core junction, increasing the delam. It doesn't need much difference in pressure to do this.
But reverse the pressure and it's a very different situation. I vacuum my skins on at half an atmosphere, you'd be lucky to get a tenth of an atmosphere due to internal cooling contraction.

Arlo said...

Has anybody come up with any visual reminders for tightening the vent screw? I was thinking about something along the lines of disc lock cord you attach onto the brake lever of a motorbike, or something that goes into the mastrack that you can screw it into.

I simply follow a routine,choose what fin to use on the day and while i have the screw driver in hand do up my vent screw,after sailing it's the reverse loosen vent screw then remove the fin.