[MarkL]

I was using a pyrex gas lens to weld aluminum today, started having problems that seemed like shielding. I've used this lens for awhile and it's always worked fine. Long story short, I discovered that by switching from the pyrex gas lens to a regular gas lens with alumina cup, it worked fine. I've examined the pyrex setup closely and don't see anything wrong, so I'm curious if there's any way to diagnose a problem like this, or if I should just surrender and throw it out and forget about it. Here's the lenses that work and don't work, this is reproducible so it's definitely something to do with the pyrex lens setup:

Radnor alumina gas lens: works
USAweld alumina gas lens: works
USAweld pyrex gas lens: doesn't work

[exnailpounder]

I was using a pyrex gas lens to weld aluminum today, started having problems that seemed like shielding. I've used this lens for awhile and it's always worked fine. Long story short, I discovered that by switching from the pyrex gas lens to a regular gas lens with alumina cup, it worked fine. I've examined the pyrex setup closely and don't see anything wrong, so I'm curious if there's any way to diagnose a problem like this, or if I should just surrender and throw it out and forget about it. Here's the lenses that work and don't work, this is reproducible so it's definitely something to do with the pyrex lens setup:

Radnor alumina gas lens: works
USAweld alumina gas lens: works
USAweld pyrex gas lens: doesn't work

I wonder if you heated up the O-ring(s) and brittled them and now you're drawing in some air? Your torch gets damned hot welding AC so you might have shrunk those rings. Just a thought.

[MarkL]

I wonder if you heated up the O-ring(s) and brittled them and now you're drawing in some air? Your torch gets damned hot welding AC so you might have shrunk those rings. Just a thought.

That's a good idea and I have an extra o-ring. It did not seem brittle at all, but it's easy to swap so I'll try that.

This is an unusual lens because it's in two parts. There's a generic body, and then different sized ends that thread on.

[cj737]

As a point of clarification, the Pyrex is the cup, the lens is separate. Pyrex cups depend upon O-rings to seal and hold them in place. The O-ring is the first likely culprit, the insulator the next. Because you shove the Pyrex down and it's only held by friction, it's imperative you get a firm seal and firmly pressed against the correct insulator. Alumina cups usually screw on toe collet body/gas lens and thus seal better.

[MarkL]

... The O-ring is the first likely culprit, the insulator the next. Because you shove the Pyrex down and it's only held by friction, it's imperative you get a firm seal and firmly pressed against the correct insulator. Alumina cups usually screw on toe collet body/gas lens and thus seal better.

I'm glad you mention this, it's always been a bit of a mystery to me. Is the contact surface between the insulator and pyrex really a potential source of air leaking? Looking at the body of the lens, there is one seal where the threads go into the torch body, and another seal where the pyrex contacts the oring. But that trapped space between the oring and the threads doesn't have access to the passageway where gas flows. Or is it possible that air makes its way through those threads and into the gas stream? It seems like wishful thinking on the designer's part if they imagine the insulator can seal against the pyrex. Maybe at such low flows and pressures, that is good enough.

[cj737]

Im not a fan of that insulator/cup personally. And whenever you install that pyrex cup, moisten the o-ring (make sure your collet body is cold before you slip your tongue over that ) then press the Pyrex on. If you don't feel some tension, the o-ring needs replacement.

I've toyed with CK gas lenses and other brands. I've settled on Miller lenses because they have a slot for an o-ring, they have a larger surface area than the CKs, and work well for sealing Pyrex cups. I use Pyrex often (always on aluminum) and with CroMo and SS, so I needed to find a solution that worked for me.

As to the comment about gas flow/pressure, I use a Pyrex cup sealed with an o-ring when I use a Fupa 12 and run 25 CFH, so that's not "low" pressure by any means. The o-ring either seals or it doesn't.

[MarkL]

And whenever you install that pyrex cup, moisten the o-ring (make sure your collet body is cold before you slip your tongue over that ) then press the Pyrex on. If you don't feel some tension, the o-ring needs replacement.

I use my little finger to moisten it, that finger is expendable.

I've settled on Miller lenses because they have a slot for an o-ring, they have a larger surface area than the CKs, and work well for sealing Pyrex cups. I use Pyrex often (always on aluminum) and with CroMo and SS, so I needed to find a solution that worked for me.

I can't find a pyrex cup made by weldcraft or miller. Where do you get those?

[cj737]

I only use the Miller lenses, but I use Furick's Pyrex cups. The #8 is quite handy and the #5 is great for tight ally. The Fupa (12) just plain rocks on stainless. All these rely on the Miller lens as it has an o-ring band. You can get them thru Mike's website.