Gas Fittings

Submitted: Thursday, Mar 03, 2005 at 10:15
ThreadID: 20927 Views:15737 Replies:5 FollowUps:2
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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....
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Reply By: Member - 'Lucy' - Thursday, Mar 03, 2005 at 10:40

Thursday, Mar 03, 2005 at 10:40
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.

AnswerID: 100949

Reply By: Member - Sand Man (SA) - Thursday, Mar 03, 2005 at 11:02

Thursday, Mar 03, 2005 at 11:02
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!

I'm diagonally parked in a parallel Universe!

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AnswerID: 100951

Reply By: Tuco - Thursday, Mar 03, 2005 at 11:48

Thursday, Mar 03, 2005 at 11:48
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.
AnswerID: 100954

Follow Up By: Ray Bates - Thursday, Mar 03, 2005 at 20:27

Thursday, Mar 03, 2005 at 20:27
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
FollowupID: 359055

Follow Up By: Tuco - Thursday, Mar 03, 2005 at 21:57

Thursday, Mar 03, 2005 at 21:57
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!
FollowupID: 359073

Reply By: Ray Bates - Thursday, Mar 03, 2005 at 20:23

Thursday, Mar 03, 2005 at 20:23
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
AnswerID: 101022

Reply By: Stuart - Saturday, Mar 05, 2005 at 02:17

Saturday, Mar 05, 2005 at 02:17
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.
AnswerID: 101191

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