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Gas Fittings

Submitted: Thursday, Mar 03, 2005 at 09:15

Alan S (NSW)

Hi,
I'm just curious and I am sure someone out there knows the answer. Why do gas fittings have an opposite screw thread? It makes no sense to me.

A few weeks ago I saw a guy at the camping spot next to me trying to unscrew his gas bottle with a wrench but he was putting pressure on the wrong direction, this could be dangerous....
ThreadID: 20927 Replies: 5
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AnswerID: 100949   Submitted: Thursday, Mar 03, 2005 at 09:40

Member - 'Lucy' replied:



Primarily so you can't accidentally connect the gas bottle to anything else, and cause a 'fubar cloud' as Truckster would so eloquently put it.

This also fits the dangerous category.

LPG ( whatever variety) is for LPG thingo's only.

It's not pretty
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Reply 1 of 5
AnswerID: 100951   Submitted: Thursday, Mar 03, 2005 at 10:02

Member - Sand Man (SA) replied:

Only some do Alan.

To complicate things even further, different brands (primus, companion, etc.) not only have a left, or right hand thread, but also male, or female fittings.
(e.g. the thread is on the inside, rather than the outside of the fitting)

Although one can buy adapters to convert from one type to the other, it does make life more complicated.

I think its a conspiracy by the different manufacturers, who "force" their format onto us as a "standard" fitting. Problem is, it's only a standard companion, or Primus fitting, rather than a universal one.

Even further, some gas bottles use POL fittings. (like the common backyard barbecue, for instance) instead of the 3/8" fitting, more common on smaller size gas bottles.

The POL fitting is only of one type and yes, you guessed it, it's a LEFT hand thread,
which gets back to your original question:- why?

bleepe, I'm buggered if I know.
Now I wanna know why too!

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Reply 2 of 5
AnswerID: 100954   Submitted: Thursday, Mar 03, 2005 at 10:48

Tuco replied:

Traditionally, and for safety reasons, flamable gases (LPG, acetylene, hydrogen, etc) use left hand threads while non flamable (oxygen, nitrogen, compressed air, etc) use right hand threads. Because of this safety factor it is impossible to install fittings to the wrong cylinder - eg in an oxy/acetylene set where there is one left hand and one right hand thread.

This has been the Australian standard for many years.

Then along comes "Primus" with their right hand threads on LPG cylinders - which goes against the safety standard! I have no idea how they were permitted to use the incorrect right hand threads on LPG equipment.

All other manufacturers, to the best of my knowledge, use the "Companion" left hand thread or the POL left hand thread for all LPG cylinder fittings.
Reply 3 of 5
FollowupID: 359055   Submitted: Thursday, Mar 03, 2005 at 19:27

Ray Bates posted:

I'm glad that someone agrees with me in stating that oxygen is a non flammable gas. Millions of people believe that it is flammable
FollowUp 1 of 2
FollowupID: 359073   Submitted: Thursday, Mar 03, 2005 at 20:57

Tuco posted:

Hi Ray - 40 years ago when in high school - we were taught that oxygen itself is a non flamable gas that SUPPORTS burning.

In the absense of oxygen - the flamable gases wont burn either.

LOL - some of my grey matter must have absorbed that insignificant bit of information!
FollowUp 2 of 2
AnswerID: 101022   Submitted: Thursday, Mar 03, 2005 at 19:23

Ray Bates replied:

Yes Primus do have to be different. I have noticed that some of their bottle are fitted with female threads. I believe they must be Americans
Reply 4 of 5
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AnswerID: 101191   Submitted: Saturday, Mar 05, 2005 at 01:17

Stuart replied:

Just to make life a little easier, if you look at the fittings you will notice that nearly all left hand thread fittings have a notch around the circumference. It takes the guess work put of it.
Reply 5 of 5

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