Welding Tips and Tricks

Are the bane of my existence. My only problem child consumable. I keep pulling them off other back caps when they need to be replaced. Looked for the size online but wasn’t able to find anything. Anybody know the size/specs for the 9/20 back cap o-rings for CK torches so I can just buy a bag of them for a few dollars??

I just use O-rings from my Harbor Freight box kit. The Viton and HNBR work well. Their nitrile ones suck.

Silicone o-rings work better, last longer, jump higher and wear capes under their dailies

I've never replaced a back cap o-ring in my life. That's only on weldcraft torches because that's all I've ever owned. But I can't imagine what you can do to make one of them leak.

I would say go to a hydraulic shop and find out what R size they are.


Most of the hydraulic shops I've dealt with have a o ring size gauge alot like a jewelers ring guage. Just a tapered pin with many flat spots on it for the various sizes.


Not sure if it can be bought or of they had them custom made.

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BugHunter wrote:I've never replaced a back cap o-ring in my life. That's only on weldcraft torches because that's all I've ever owned. But I can't imagine what you can do to make one of them leak.

With both of my CK 20s, the o-ring stays lodged in the end of the torch every time I remove the back cap. This causes the o-ring to grate against the threads with each journey to and fro, and eventually tears them up pretty good. I may try using just a tiny bit of high temp grease to see if that helps any.

I'm a bit surprised no one else has this issue.

The o-rings may be 009s based on my crude measurements. Bag of 25 of those (high temp, as well) is $3 from McMaster. CK does sell replacements...'I think for $2 per O-ring

Spartan wrote:

BugHunter wrote:I've never replaced a back cap o-ring in my life. That's only on weldcraft torches because that's all I've ever owned. But I can't imagine what you can do to make one of them leak.

With both of my CK 20s, the o-ring stays lodged in the end of the torch every time I remove the back cap. This causes the o-ring to grate against the threads with each journey to and fro, and eventually tears them up pretty good. I may try using just a tiny bit of high temp grease to see if that helps any.

I'm a bit surprised no one else has this issue.

The o-rings may be 009s based on my crude measurements. Bag of 25 of those (high temp, as well) is $3 from McMaster. CK does sell replacements...'I think for $2 per O-ring

i would speak to CK about that issue.

What does the inside of the torch look like at the rear? That o-ring needs to climb up over about a mile of threads to leave that groove cut in the cap. Seems to me there's got to be something wrong with the bore at the rear of the torch.

I find with the o rings if I out them in dry they stick a little bit. If I lick my finger and wet them ever so slightly they don't stick.

graphite might be a good choice for lube as well

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BugHunter wrote:What does the inside of the torch look like at the rear? That o-ring needs to climb up over about a mile of threads to leave that groove cut in the cap. Seems to me there's got to be something wrong with the bore at the rear of the torch.

I'll snap a pic next time I'm at the shop. I think the rubber in there is just a bit too tight.

Is there a burr on the torch bore from the parting operation ( dead insert ) ?

I would use an alcohol soaked q-tip, to clean the inside rear of the torch. Then apply a light greasy lube to the O-ring. Personally, my first choice is DC4 (Dow Corning#4) compound. Very useful stuff to have around a shop.

How often are you taking out your back cap? I only loosen mine to change tungsten. But I don’t take it all the way out.

VA-Sawyer wrote:I would use an alcohol soaked q-tip, to clean the inside rear of the torch. Then apply a light greasy lube to the O-ring. Personally, my first choice is DC4 (Dow Corning#4) compound. Very useful stuff to have around a shop.

That's exactly what I'm going to try. I do think it is an oddity with those torches though. Only happens with my CK 20s.

Poland308 wrote:How often are you taking out your back cap? I only loosen mine to change tungsten. But I don’t take it all the way out.

Not often at all. Pretty much only when I need to actually change the back caps. I loosen the back cap and front load everything when swapping tungstens, collets, etc.

I guess I don’t change my back cap. I just run the stubby flat one. I cut all my tungsten in half and point both ends. I do keep a different torch head a 26 with a long cap on it for heavy work, but I just change the whole torch.

Poland308 wrote:I guess I don’t change my back cap. I just run the stubby flat one. I cut all my tungsten in half and point both ends. I do keep a different torch head a 26 with a long cap on it for heavy work, but I just change the whole torch.

I do the same with the tungstens, but have to use the medium back cap with the half tungstens due to my stubby GL setup. That's probably my rig 90% of the time. Only shift to the button back cap when space is a concern, and the long back cap when welding thicker AL.

On my setup about the biggest issue I have is the collet will set in place collapsed. At that point, I can't even pull the tungsten out the front because it won't expand enough to let the paint through. So I have to remove the back cap to remove and resharpen. Happens all the time. After a gazillion times now, I've still never replaced an o-ring. And I would say that includes 12-15 torches over the years.

I would probably either replace the torch (or be ready to) or take one of those fiber wheels and deburr the rear of that bore where the o-ring sits. Even if you ever so slightly bell-mouth the back of the torch, it's probably still fine as long as that surface is smooth and doesn't try to hang on to the o-ring when you remove the cap. And it goes without saying the lube idea above is a must. I have Dow food-grade grease here as well as some DuPont Teflon-Silicone spray that's simply awesome lube. I use it in locks (doors) and it lasts a decade keeping tumblers and mechanisms working nicer'n new. I might have to get some of the stuff recommended above next time I order from McMaster or MSC.

I had exactly the same problem first time I stripped my CK20, hadn't even used it yet.
Just stuck a cheap back cap out of one of those multi accessory kits in from rapid welding and never had the problem again.

Hello,
I've read this topic after searching the same information and here is what I've found:
https://do-it-up.com/stuff/welding/tig/ ... es/orings/
I don't know if the dimensions are exact, I've ordered 2 types of o'rings for a WP-20 and will try them.

Hope it'll help some people in the future !

I've received the O'rings I ordered on Aliexpress in this shop (not affiliated, feel free to order where you want):
https://www.aliexpress.com/item/1005003 ... pt=glo2fra

I've chosen 2 types:
OD 8mm ID 4mm (CS 2.0mm)
OD 9mm ID 5mm (CS 2.0mm)

Until now I've just tried the first ones and it works with no problem. I've just added some high quality silicon grease (Loctite 8104) on the ring and that's perfect.
I'll try the OD9mm later...