How to identify two-stage regulator

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I'm trying to determine if these old regulators are single or two-stage.  I posted pics a few days ago and am considering getting them rebuilt, but I know the cost will come close to just buying a new set.  These seem to be in decent shape (dirty though), and if they are two-stage it might be more worthwhile to refurb them.It appears that single-stage regulators have a flat back and two-stage ones have a longer back, like these.  I'm not sure if that is the best way to verify though, and I haven't been able to find anything about these particular ones on the web.Here are pics of the oxygen regulator.Thanks. Attached ImagesHobart Handler 210Lincoln AC-225Smith Torches/Regs
Reply:Looks like a single-stage based on comparing to the Seal Seat catalog.Since it's rebuild bait, take it apart and have a look. Remove that back cap and if there is no diaphragm, than it's a single diaphragm therefore single stage. You can back off the t-handle too and open the other side.  Explore! Taking apart old equipment is a great way to see how it works.
Reply:I don't know the exact parts terminology, but a two-stage regulator houses two separate pressure springs. Therefore, a two-stage regulator will often have a long bulky barrel, or else the regulator's back will show some evidence of having a fixed first-stage regulator spring housing and its cap.I would say that the pictured Smith regulator is single stage, its two-stage counterpart would have a "capped bump" below center, where a bulky primary regulator section is located. Anyway, why the  rebuild? If Smith is clean, doesn't leak and doesn't creep, put it to work.Good LuckLast edited by denrep; 06-14-2011 at 06:19 PM.
Reply:Good idea.  I've been tempted a couple of times to pressurize it, but due to the grease in the t-handle and diaphragm I'm not going to risk it.  I'll open it up and take a look.Thanks.Hobart Handler 210Lincoln AC-225Smith Torches/Regs
Reply:Denrep, my post crossed yours so in response, I was tempted to just try it, but the threads on the oxygen regulator adjusting screw are worn and someone in the past has caked heavy grease in there presumably to help take out some of the slop.  I've cleaned up this area somewhat, but I don't have any way to know how much is inside.  I know that area is not pressurized directly, but again I'm just not sure how safe it would be.  My guess is that it would work fine, and it's apparently been used in its current greasy state, so it would "probably" be OK.Thanks.Hobart Handler 210Lincoln AC-225Smith Torches/Regs
Reply:I don't know if I've ever seen a regulator with worn out threads, somebody must have actually backed the handle off every day.  In the regulator game it's one strike and you're out. Myself, I'd write it off.Good Luck
Reply:Yeah, that was my take on it too.  The acetylene screw is perfect, but for some reason the oxy one is visibly worn (looks like a tapered thread at this point).  I may take it apart out of curiosity, but I'm leaning more toward not putting any money into them.Hobart Handler 210Lincoln AC-225Smith Torches/Regs
Reply:I went ahead and took the oxy regulator apart, and now it's more clear why the adjusting screw is worn.  The spring it's pushing is really massive (can't begin to compress it by hand), probably 3/16 or 1/4 inch diameter steel.  The soft brass threads are pushed over, maybe just from over-tightening, but it's easy to see that they would naturally deform over time.There is just one large diaphragm, so single-stage.  The internals don't look too bad, so I'm sure it could be rebuilt, but I'll have to think about it still considering the cost versus new.The knurled fitting on the back seems to be a pressure-relief vent/valve, so I'm assuming it's a safety feature.  Looks like it might tend to blow out that direction.  I noticed my other (cheap) HF regulators have this also.Hobart Handler 210Lincoln AC-225Smith Torches/Regs
Reply:Originally Posted by thomasalva. . . now it's more clear why the adjusting screw is worn.  The spring it's pushing is really massive (can't begin to compress it by hand), probably 3/16 or 1/4 inch diameter steel.  The soft brass threads are pushed over. . .