Welding/cutting torch packing seals.
#1
I'm working on cleaning up my Harris torches for my full size oxy/acet set. They were getting pretty oxidized and cruddy looking after all this time (purchased in 1985) and needed rebuilding anyway. O-rings and valve stem seals (packing) were getting stiff and hard to move. I bought rebuild kits (o-rings & washers) but they don't include new seals/packing for the valve stems. To get those you have to buy new stem and handle "assemblies".
Wanting to get this done quickly I did buy new valve assemblies.

But it bugs the daylight out of me to just throw away the original valves. I'm thinking of taking them apart and making my own new packings from some PFTE (Teflon) rod that McMaster sells for ~ $2.00 per foot. Just to have an extra set of valves on hand - in case...

Just curious if anyone else has been there, done that and maybe has any tips for success? I'm assuming reaming the ID for a close fit to the stem is job #1.
Willie
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#2
I recommend talking with the repair techs at your local welding supply.  This is something they probably do on a daily basis.
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#3
Last time I did that (several years ago) was when my acetylene regulator started creeping on me. Went over there to pick up a couple of regulator rebuild kits. Nope. They don't (WON'T) sell parts. They send everything out for repair and then charge you 75% of what it would cost to buy new regulators. As far as I know most LWS won't sell gas control parts because of the liability, which is understandable I suppose.

Even the places that do sell parts online and offer rebuild services, only sell valve assemblies as far as I know. The parts breakdown from Harris only shows them as an assembly. Since they are a SOB to get apart without damaging the stems I doubt any of those places are going to put the time and effort into making their own seals/packing. Not to mention the liability. I did have them apart to clean and lube them once before when they started to stiffen up. But the packing have gotten to where they are rock hard now. No idea what material the originals are made of.

The assemblies aren't all that expensive (~ $16 - $18 each) to replace which I'm doing anyway. But since I can afford to take my time with the old parts, I thought why not give it a go? Only problem is I've never tried machining PFTE before.  Sweat
Willie
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#4
What are you using as “lube” ?

My understanding is that no oils are allowed anywhere near oxygen valves, hose couplers and regulators.
Andrew Mawson, proud to be a member of MetalworkingFun Forum since Oct 2013.
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#5
(09-06-2019, 01:31 AM)awemawson Wrote: What are you using as “lube” ?

My understanding is that no oils are allowed anywhere near oxygen valves, hose couplers and regulators.

Right you are Andrew. Hydrocarbon (petroleum) based oils should never be used around oxygen. It is a fuel source that can be ignited quite easily when impacted with oxygen. Bad ju-ju.

Instead I am using Krytox which is a fluorinated synthetic grease that is inflammable, chemically inert, and safe for use in oxygen systems. I believe it is commonly used in the aerospace industry among others due to it's resistance to both gaseous and liquid oxygen. I can tell you Krytox is extremely expensive though. But when nothing else will do...

I also used it when I rebuilt my regulators. I only wipe enough on to put a 'sheen' on the surface of seals & slip rings before assembly. You certainly don't want to glob it on. I have a .5 oz (14.8 ml) syringe of it that would last me several hundred lifetimes. But that was the smallest amount I could buy.
Willie
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#6
The Teflon that McMaster sells is quite hard. I have some, and while it machines fairly well, it's not soft, like Delrin.

I would think that you would want something softer for the packing, to kind of "squish" around the stem as you tighten the packing nut.
Full of ideas, but slow to produce parts
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#7
(09-07-2019, 07:59 AM)rleete Wrote: The Teflon that McMaster sells is quite hard.  I have some, and while it machines fairly well, it's not soft, like Delrin.

I would think that you would want something softer for the packing, to kind of "squish" around the stem as you tighten the packing nut.

There are different grades of Teflon and McMaster carries some of them.  You may want to consider Durable PFA.  Just a thought.
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#8
(09-07-2019, 07:59 AM)rleete Wrote: The Teflon that McMaster sells is quite hard.  I have some, and while it machines fairly well, it's not soft, like Delrin.

I would think that you would want something softer for the packing, to kind of "squish" around the stem as you tighten the packing nut.

You must have a different flavor of Teflon. Delrin hardness (McMaster): Rockwell R120-R122 (Hard)
1/2" PTFE rod (McMaster): Durometer 50D-65D (Medium Soft)

The real fly in the ointment though is that Delrin is flammable and is non-self extinguishing. It doesn't stop burning until available oxygen is used up or removed. Note in the description - "Must not (be) used for Oxygen service."

.pdf   Valve Seat Material guide.pdf (Size: 88.76 KB / Downloads: 1)
Willie
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#9
(09-07-2019, 10:12 AM)Dr Stan Wrote: There are different grades of Teflon and McMaster carries some of them.  You may want to consider Durable PFA.  Just a thought.

Thanks Stan but...

1/2" PTFE rod ~ $2.56 per ft.

1/2" Durable PFA rod ~ $56.92 per ft. Happyno
Willie
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#10
YOUZER! Jawdrop
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