O-Rings - What kind is best to use in a WTC?

[mickelsen]

Can anyone advise me as to what kind of O-ring is best to use for the end caps in a WTC? I went to McMaster-Carr and there are about a thousand different kinds available and I have no idea what would be best. Can anybody tell me what is usually used by knowledgeable sub builders?

Thanks in advance.
Mark

[anonymous]

Hi Mark,

Have a look at

Hi Mark,

Have a look at www.pressureseal.com
Go to the catalog section, O ring section, and find the design guide. It will give you everything you probably need to know for O ring seals. Don't worry about swelling allowances - you are using water.

For large diameter WTC use , you may find that making your own O rings (O ring cord cut slantwise and cyanoed? may be more easily adapted to your designs.

IMHO don't use O rings for rotating shafts (too much friction in our submarines) use Simmering oil seals.

Again IMHO bellows do a a better job for servo push rods.

Suggest you also search this board for "WTC" to get other people's ideas.

David

[mickelsen]

Hi David,

Thanks for your most

Hi David,

Thanks for your most informative reply. I hadn't thought of making my own o-rings. That may be just the ticket.

I agree with you about the Simmering oil seals but I haven't been able to find a source for them here in the USA. Do you know of a source where I can get them?

Thanks again,
Mark

[anonymous]

Hi Mark,

Yes, if you have

Hi Mark,

Yes, if you have access to the full range of O rings and you can machine slots i.e you have access to a lathe then the approach in the design guide is good.

My WTC, which is stil going strong after several years (with the original home made O rings) , was not made on this basis. It uses radial seals. You can make a sandwich of several polycarbonate disks with one of the disks of smaller diameter to form a slot for the O ring. Stick the disks together when you made the O rings and you can push the assembly fairly easily into the outer tube.

It is a a bit of a trial and error process and I would now prefer to use my, recently purchased, Taig (Peatol in the UK) lathe instead.

As I recall this topic is discussed elsewhere in the forums and is the approach I think Fung Pang used, as well.

Have a look at the Simmerit web site for US stockists. I have found them excellent but expensive (£2 to 3 in the UK).

You may find other and cheaper sources since they are are just an oil seal with a rubber lip which moves on the shaft. A spring keeps the rubber lip in gentle contact with the shaft. Don't run the shaft at too high a speed ie use a reduction gear from the motor and you will have a gas tight , thoroughly reliable seal available off the shelf.

David

[anonymous]

Sorry it is Simrit of

Sorry it is Simrit of course!

www.simrit.com

David

[mickelsen]

Thanks again, David. I appreciate

Thanks again, David. I appreciate your help.

I looked on the Simrit website but couldn't find any US distributors. I have a friend in the UK that is willing to order some for me, but if I didn't have to bother him it would be better.

I don't have a lathe. I wish I did but it's not in the budget right now (and probably not for a long time), but Fung Pang describes a method using a jig and a Dremel drill press, which I do have. We'll see how good it works for me.

Mark

[anonymous]

That's good . I think

That's good . I think you will find the non-lathe approach is fine - it just takes longer!

I'm still using my original WTC made this way 5 years on.

I think Jim Butt did a nice article in the SCR also on WTC's - sorry I can't remember the issue.

If you can't find a Simrit distributor, I suggest you look to US made oil seal suppliers. Maybe try your local car parts distributor also. The only problem is that we only need a small diameter shaft (say 1/4")

BTW the inspiration for the oil seal idea is from Norbert Bruggen's book Model Submarine Technology.

You could of course buy the whole WTC ready made - but modellers need challenges

David

[mickelsen]

Hi again,

I have a related

Hi again,

I have a related question concerning o-rings. I had always assumed that the groove that you cut for the o-ring to sit in is best cut with a circular cross section. As I have been reading some of this information I've gotten some indication that it is better to have a rectangular cross section. Would anyone like to comment on what is the best shape for the groove?

Thanks again,
Mark

[crazy ivan]

Mark,

One resource for O-ring info

Mark,

One resource for O-ring info (and probably more than you would ever want to know) can be found at This Website.

[anonymous]

Nice information site also, Ivan!

I

Nice information site also, Ivan!

I think it has to be rectangular to allow the ring to be squashed,

David