How to determine O-ring size

[mickelsen]

This is a newbie question. How do you determine the right size of O-ring to use for the end caps in you WTC. I have pieces of polycarbonate that are 2"od and varies between 1 7/8" and 1 55/64"id and 2 1/4"od and varies between 2 1/8" and 2 7/64"id. I want to make a mating bulkhead that will connect the two together without leaking but be disconnectable like an endcap. I don't know how to figure out what size of rubber O-rings to use on each side. Can someone tell me how you decide what sizes to use to make endcaps watertight but still removable?
Thanks,

[T. Schulte]

Mark, Happy Holidays from Colorado. In Denver we have a source for O-rings and any other type of seal you might need like pushrods. or prop shafts. They also have a size chart that will give you all the info you need for the depth of the O-ring groove and dimensions of yor end cap and poly-carb tube. www.rocketseals.com on their search engine type in "size chart" it will give you standard and metric options. These are a great bunch of people, always had time to answer my questions. Hope this helps. Ted Schulte Westminster, CO.

[Subculture]

Bloody imperial measurements, why can't you guys get with the metric system like the rest of the known universe!!

Rant over.

This is one of those areas of submarine design where it really pays dividends to know exactly what you're doing. It's not hard, but there quite a few things you need to study to ensure you have a successful result.

Read this guide-

http://www.jameswalker.biz/docs/jwco/o_rings_full_doc.pdf

Very useful document that. To simplify things a bit, you will be wanting nitrile o-rings (Buna-n in U.S speak), no higher than 80 shore, preferably 60-70 shore and about 1/8"-3/16" thick. Look carefully at the sections which deal with tolerances. Get it wrong and you'll end up with either a leaky cylinder or an endcap that is too tight. Fortunately our application is quite undemanding, so you should be okay.

[T. Schulte]

One of the brands out ther is Parker O-rings. They have a handbook in pdf format www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf IT's not for the faint of heart. You need a degree to understand some of the contents,but I managed to get through it. That's where you'll find all the measurments for what you're doing. I was in error when I said this info was on the Rocket site. Sorry... Ted
P.S. As for that crack about the metric system. Don't worry it will never catch on! We don't want to be like the rest of the Universe any way. This is THE UNITED STATES OF AMERICA !!!

[He Who Shall Not Be Named]

And ... just where did we get the imperial system of measurements again, Andy?

David,

[Albion]

And ... just where did we get the imperial system of measurements again, Andy?

David,

Yes, and even we gave up and went metric, but maybe because one our boys had the idea, (see john Wilkins)

http://en.wikipedia.org/wiki/Metric_system

Vive la Brits

[He Who Shall Not Be Named]

Well then, why did you go to all the trouble to kick the Nazi's ass off the island if you go metric anyway. What's wrong with you people!?...

[Subculture]

Why did you go to all the trouble of kicking our arses out of it in 1776?

[He Who Shall Not Be Named]

Touché.

David,

[Outrider]

Re: John Wilkins. You forgot to include the rest of the story... "The idea of a metric system has been attributed to John Wilkins, first secretary of the Royal Society of London in 1668. The idea did not catch on, and England continued with its existing system of various weights and measures." It took the Revolutionary French to adapt the idea to their own purposes. Like many things from that radical movement, adoption of the metric system did not go smoothly, even in La France. Under Napoleon, the French reverted to their old ways, and they did not resume use of the metric system until 1837.

Don't go short selling the U.S. on metrication. (Who knew there was such a word?) The U.S. adopted the metric system in 1866 in that the government mandated acceptance of the system without making its use mandatory. (The US was also an original signatory to the relevant international treaty, as well. Note that the UK did not sign up to this one right away. http://www.bipm.org/en/convention/me...seventeen.html) But without mandatory use, and a functional, if obscure, system of weights and measures in place, it's no wonder we've been so slow to get around to it.

And don't forget that there are some decidedly non-metric systems that work just fine and won't be changing, such as the nautical mile, and the system of degrees that measure latitude and longitude that we use in aviation and at sea.

Though the Brits have more fully adopted the metric system, I'm not taking any grief from them on our lack of "progress" as long as they continue to weight themselves in "stones" and post their speed limits in good old miles per hour. Besides, they still haven't figured out how to drive on the right side of the road. And even though everybody gets bulk soda and wine in metric units, there's still the pint, which I shall be having at the appropriate time.

[Subculture]

I'll be the first to agree that we have a very strange mix of measurements. Some of these have been pointed out. We still refer to miles, and measure fuel consumption in miles per gallon, our gallon being larger than the U.S gallon, just to confuse things a little more.

When we refer to our cars engine capacity however, you'll get a blank look here if you refer to cubic inches. Here, engine capacity is referred to in cubic centimetres or litres.

In engineering terms however, it's much better to adopt a single system- results in less screw-ups. The metric system is totally logical, and very easy to understand. Converting from dimensions to weight to volume to pressure etc. is straightforward.

As someone who was brought up understanding both systems of measurement, I'm able to appreciate the difference. I only work in imperial when forced to.

I've noticed that colleagues in their twenties have no idea about imperial measurement, which suggests it's no longer taught in schools.

[Outrider]

Though American, I've spent much time overseas, starting in Okinawa when I was nine years old. I remember buying cleats in a Japanese store based on the length of my foot in centimeters. How easy was that? I was hooked for life. Metric tools are great for the same reason. Was that a 5/16 or 1/4 inch wrench? Millimeters make more sense than fractions when you're working on a dirty piece of equipment in an uncomfortable position hoping you won't strip something or rip the skin off your fingers. I'm happy to use the metric system where it makes sense to do so.

[T. Schulte]

Way off topic !!! Sorry, my fault. Never again. T.S.
How about those O-rings?

[He Who Shall Not Be Named]

F all of ya! ... the Imperial system dies with me, damit!

David,

[Outrider]

Way off topic !!! Sorry, my fault. Never again. T.S.
How about those O-rings?

Point taken and nicely put.

Let me try to make a connection, though. It seems like it would be a lot easier to buy O-rings if they were sized in metric units in all three dimensions. (At least some) bearings are done this way. For a proper fitting O-ring, inner and outer diameter matter, as do thickness. Three fractional measurements in small sizes could make my head hurt...

My limited experience with the O-rings in SubDrivers seems to confirm this point. Get the O-ring wrong and your electronics get wet. Get the electronics wet and you have an expensive, inoperable mess. It may be a mess you can't even find. Watertight integrity checks make a lot of economic sense.