fly2low Posted July 23, 2018 Report Share Posted July 23, 2018 I have a 20 or 30 gal lp tank mounted between the frame rails of my RV. I need to disconnect the pressure regulator and solenoid from the tank - address a small leak. I am not sure of the thread direction into the tank. Is it counter threaded like smaller LP tanks, or "Righty Tighty"/normal. Tried moderate pressure in both directions without movement. Quote Link to comment Share on other sites More sharing options...
fly2low Posted July 23, 2018 Author Report Share Posted July 23, 2018 It is a Manchester tank. Can't get to their web site Quote Link to comment Share on other sites More sharing options...
Kirk W Posted July 23, 2018 Report Share Posted July 23, 2018 (edited) CAll combustible gas fittings are left-hand thread. Edited July 24, 2018 by Kirk Wood Quote Link to comment Share on other sites More sharing options...
fly2low Posted July 23, 2018 Author Report Share Posted July 23, 2018 thought so but did not want to lean into it until I confirmed thanks Quote Link to comment Share on other sites More sharing options...
fly2low Posted July 23, 2018 Author Report Share Posted July 23, 2018 fixed Quote Link to comment Share on other sites More sharing options...
Kirk W Posted July 23, 2018 Report Share Posted July 23, 2018 10 hours ago, fly2low said: fixed 👍 😀 Quote Link to comment Share on other sites More sharing options...
Dutch_12078 Posted July 23, 2018 Report Share Posted July 23, 2018 17 hours ago, Kirk Wood said: All combustible gas fittings are left-hand thread. I think that's a bit confusing, Kirk. POL fittings are left-hand thread, but ACME fittings are right-hand, as are the standard black pipe and flare fittings commonly used for combustible gases. Off hand, POL fittings are the only ones I can think of that are left-hand threaded. Are there others? Quote Link to comment Share on other sites More sharing options...
GeorgiaHybrid Posted July 23, 2018 Report Share Posted July 23, 2018 (edited) acetylene tanks for one have left handed threads. Here is an excerpt from an esab handbook: All CGA standard connections for oxygen and for oil- free inert gases carry right-hand threads; all CGA standard connections for acetylene, other fuel gases, and for gases which may have been compressed through oil-lubricated compressors carry left-hand threads except for the CGA 300 acetylene cylinder/regulator connection, and the two cylinder/regulator connections used with small acetylene cylinders. Left-hand threads are always indicated by a groove cut in the middle of the connection nut or in the hex section adjacent to the connection thread. All of the larger acetylene tanks use a CGA 510 fitting Edited July 23, 2018 by GeorgiaHybrid Quote Link to comment Share on other sites More sharing options...
Dutch_12078 Posted July 24, 2018 Report Share Posted July 24, 2018 Thanks for the info, GH, but that doesn't explain why all the non-POL LP fittings used in RV's are right-hand thread including the ACME fitting on DOT cylinders and the fill valve fitting on ASME tanks. Check these common RV parts out: https://www.etrailer.com/faq-common-rv-propane-fittings.aspx Quote Link to comment Share on other sites More sharing options...
Lou Schneider Posted July 24, 2018 Report Share Posted July 24, 2018 (edited) ACME fittings are only used on propane tanks so there's no possibility of connecting them to another type of tank. POL fittings are the same diameter as those used on oxygen and non-flammable tanks. The left hand thread is to avoid getting the flammable and non-flammable connections confused. Edited July 24, 2018 by Lou Schneider Quote Link to comment Share on other sites More sharing options...
Dutch_12078 Posted July 24, 2018 Report Share Posted July 24, 2018 Agreed, Lou, and as far as I can see, those are the only unique fittings commonly used for RV's. I could also include the unique fitting used for the disposable cylinders used on grills, lanterns, etc., I suppose, but those are right-hand threaded as well. I still haven't seen anything to indicate that "All combustible gas fittings are left-hand thread.", at least when it comes to RV use. The POL is still the only LH fitting I'm aware of. Quote Link to comment Share on other sites More sharing options...
Kirk W Posted July 24, 2018 Report Share Posted July 24, 2018 9 hours ago, Dutch_12078 said: I still haven't seen anything to indicate that "All combustible gas fittings are left-hand thread.", at least when it comes to RV use. The POL is still the only LH fitting I'm aware of. I suppose I should have narrowed it to the conversation I was addressing. In the context of the question asked, the answer was correct, but only there. Quote Link to comment Share on other sites More sharing options...
Dutch_12078 Posted July 24, 2018 Report Share Posted July 24, 2018 15 minutes ago, Kirk Wood said: I suppose I should have narrowed it to the conversation I was addressing. In the context of the question asked, the answer was correct, but only there. That would have helped clarify your comment, but note that the POL is the only left-hand fitting, even in that narrow context. Even the valve itself is right-hand threaded where it screws into the tank. I'd hate to see someone damage an LP tank or fittings thinking they're all left-hand thread. Quote Link to comment Share on other sites More sharing options...
Ray,IN Posted July 27, 2018 Report Share Posted July 27, 2018 I just had the fill valve replaced on our 41G ASME propane tank, the valve has right-hand threads where it screws into the tank. When deciding whether you are working with left or right-hand threads, look at any exposed threads. The threads that slope towards the tank are pulling the fitting into the hole. Quote Link to comment Share on other sites More sharing options...
Hot Rod Posted August 13, 2018 Report Share Posted August 13, 2018 (edited) Right hand ACME connections are fill only connections. Left hand connections for propane and other fuel gasses are only on withdrawal connections, or connections that are used for both. The only exception to that rule are portable DOT cylinders (like your 20# and 30# cylinders) that have the newer hand tight plastic connectors for RV and grill use. Kirk is correct that all fuel gas withdrawal connections are supposed to be left hand threaded to avoid dangerous mixups. The government figured our a few decades ago that the average idiot with a gas grill had no idea what a left thread is at all or how to use it, and we had do dumb down national fuel gas standards for said idiots. And that last comment is NOT intended for anyone on this forum, as a former long time propane professional, I'm talking about the dangerous idiots I met on the job who tried to blow themselves up on a regular basis. Folks on this forum have the good sense to ask questions. Edited August 13, 2018 by Hot Rod clarity Quote Link to comment Share on other sites More sharing options...
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