Acetylene regulator

You didn't get any other replies, probably because most folks would be afraid to give advice on this one. This situation is potentially so dangerous that they probably don't want to get involved. I know I wouldn't unless I say this: Either throw the regulator away immediately or take it and the tank to your welding supplier for advice. I assume that you must have been using the tank on its side to need to ask this question.
Pete Stanaitis -----------------------
Rob wrote:

How do you figure that? An MC tank is barely larger than a propane torch tank and only holds 10cf in the standard fill. Hard to imagine much of anything so dangerous that one would be afraid to give advice. (Lack of a round tuit is the reason for my delay) Hard to imagine much danger, period.
I used to own a compressed gas distributorship. Does that count?
Bad assumption. Especially on MC and E tanks, too rapid a withdrawal will cause acetone carryover. In any event, I've never had any problems operating an MC tank on its side and firing either a Prest-o-lite or a mini oxyacetyelene torch, both low demand applications. Too little acetone too tightly bound to matter much.
You didn't say how much the pressure is varying. Aged regulator needle valve seats (neoprene or equiv) will get soft. This results in the needle sticking, increasing the force needed to unseat the needle. The result can be pressure pulsations instead of smooth linear regulation. The seat has to be resistant to acetone because the acetylene is saturated in acetone vapor when it exits the tank.
I've seen otherwise OK regulators that would pulse when the tank was almost empty. If that's the case here then your regulator might be OK.
NO, bad threads are not involved. No CGA gas fitting relies on the threads for sealing. The seal is a metal-to-metal joint and the threaded nut simply provides the force necessary to hold the two mating parts together. Only a snug fit is needed. If you're having trouble holding the tank then you're tightening WAY too tight.
The tank fitting has a concave spherical mating surface and the spud (the part screwed into the regulator, also called the nipple) has a mating convex surface. Both must be clean, smooth and symmetrical to achieve a seal. Inspect both for burrs, dirt, digs and warpage. If you tighten the nut finger-tight and then spin the regulator back and forth a little, you should see a continuous shiny band of bright brass on both the tank and spud. If you don't see these shiny rings then one or both mating surfaces probably have been damaged, either from dropping or overtightening.
Given how cheap MC regulators are, I'd not spend much time on this. Do just enough to verify that the tank valve's mating surface is OK, then toss the regulator and get another one.
John -- John De Armond See my website for my current email address

Answering "how do you figure that?" A friend of mine brought a failed acetylene regulator to a meeting a couple of years ago. He told about how quickly the regulator caught on fire and how hard it was to get to the valve that was in the middle of the fire. Acetylene is one of the most dangerous flammable gases I know about. And you certainly don't want a regulator to tell you that you've got 15 psi when it's really 40!
Pete Stanaitis -----------------------------
Ne>

I wasn't running the tank on its side, I was transporting it on its side and only waited for about an hour before attempting to use it. This is a little peanut rig that I bought new and hadn't used for several years. It worked fine the last time I used it. I guess I'll take it in.
Thanks, Rob