View Full Version here: : Why Left Hand Thread
Hi guys, just a question, what if ever is the reason for the thread on a gas bottle to be left hand thread. :shrug:
Every time i hook it up i wonder, why :shrug:
09-07-2012, 09:17 PM
I imagine it is so the less mentally endowed among us cannot inadvertently screw an incorrect fitting to a gas bottle.
09-07-2012, 09:33 PM
Probably to ensure that you don't connect a combustable gas to an oxygen or air hose / fitting. This obviously would have a high probability of rendering your person in a slightly less than salubrious state.
09-07-2012, 09:36 PM
Going from memory at uni
left hand thread was for flammable gases and right hand for inert or oxidising gases. But that was 30 yrs ago:sadeyes:
09-07-2012, 09:43 PM
It is still so, prescribed by an Australian Standard, AS2473
I asked the same question to Monte Wilson several years back.
Monte's family is steeped in the bottled gas business.
The answer was so that fuel gas and oxygen bottles would not get mixed up.
09-07-2012, 10:14 PM
Yes, hydrogen and acetylene are also LH thread. In fact thread types and sizes are so arranged that one cannot connect any gas by mistake, even if it is nominally safe. So nitrogen, argon and carbon dioxide are different and gaseous CO2 is different from liquid take-off CO2. And of course cylinders are colour coded.
The left hand thread connections are all made of brass (I think) because the metal is too soft to produce a spark which could ignite flammable gas.
So with a left hand thread you cannot attach a steel connection - which should all be right hand threads so this cannot happen.
Ah, Gary you are getting closer, that dose make some sense of it.
Thanks guys for your responses
10-07-2012, 01:28 AM
You memory is intact, still applies.
10-07-2012, 11:52 AM
You all seem to have got the correct answer
Here is another LH/RH regulation that few of you will know
We have a dual water system fresh/recycled. The tap fittings for the recycled are all LH (unless you are a naughty boy and change them). So you don't fill the caravan with recycled water? However I believe the recycled water is probably safer than most other countries mains.
The problem is the LH fittings are many times the price of RH fittings (supply and demand) and the tap handle is removeable. These removeable tap handles I believe are made from gold judging by the price and if you leave them on the tap they disappear over night.
Well Barry I did not know that either, i expect there are many of these different threaded items around all for their specific reasons.
10-07-2012, 02:27 PM
I'll have to agree, the oxygen is pretty much what causes flammable substanes to be flammable. LPG (C1 - C4 Hydrocarbons) is Really nasty when it burns, wouldn't want to mistake it with something inert.
Well there ya go, one learns something new every day.
10-07-2012, 08:41 PM
Left hand threads on acetylene (fuel gas) are lefthand thread and is made from brass and all fittings are made from brass. If the fittings where made from copper the acetylene will react with copper to form copper acetylide and is potentially dangerous more so than acetylene
Quote from wikipedia
Copper(I) acetylide, or cuprous acetylide, is an inorganic chemical compound with the formula Cu2C2. It is a heat and shock sensitive high explosive, more sensitive than silver acetylide.
Copper acetylide can form inside pipes made of copper or an alloy with high copper content, which may result in violent explosion. This was found to be the cause of explosions in acetylene plants, and led to abandonment of copper as a construction material in such plants. Copper catalysts used in petrochemistry can also possess a degree of risk under certain conditions.
Teacher mode off
10-07-2012, 08:51 PM
What about LH threads on the LH wheels of Isuzu trucks whilst we are on the subject.
I wonder what is considered high?
Brass has 50 - 90% copper depending on the alloy...
10-07-2012, 09:17 PM
Simon I believe the mixture as to be below 70% copper
Now Kev, that is a good point, my brother a truck like you say, and he tried in vain to loosen the nuts only to find that he was going the wrong way.
11-07-2012, 08:56 AM
So that they do not loosen whilst travelling.
Oh, and it is not just Isuzu trucks.
That may be so, but only a few vehicles have LH threads, while most are RH, and they don't seem to loosen whilst traveling. :shrug:
11-07-2012, 02:58 PM
I think you'll find quite a lot of vehicles have LH threads on that side Leon. Seems to be mandatory over a certain tonnage or type of vehicle. Only one I ever drove at work was a Mazda T3500. Running empty it had horrible vibration due to the harder springs, probably the reason for the LH threads as a bit of fretting of the locking surface could make them loose enough to start spinning off. Just a guess.
11-07-2012, 03:54 PM
LH threads were on cars up til' the 50's. The car wheels after that era were designed to "spring lock" the nuts. That is why cars are all RH threads now.
Truck wheels are heavier and it can still be successful but various country legislation demands the additional safety of LH threads.
OK that is cool, just wondered.
11-07-2012, 09:00 PM
Thanks for the replies
Its all clear.
12-07-2012, 09:23 AM
Left hand threads on car wheels probably save a lot of lives in the early days. The natural flexing of the wheels, that were supported by the studs only, meant that there was a tendancy to slowly undo the nuts on that side if they in any way loosened if the thread was RH when the car was travelling forward and once it started it would only be a couple of miles before the wheel came off.
12-07-2012, 10:13 AM
Some more info Leon,
Large vehicles are subject to high temperatures on the wheel hubs. This can loosen the nuts. LH threads are self tightening (due to precession.)
Race cars often have the two different threads as well.
Sometimes after changing a wheel, and even though the nuts are tightened, they will loosen after 150 Klms. Usually after long periods of heavy braking.
Early cars were prone to losing wheels, until manufacturers installed LH threads. There were many fatalities from those accidents in the early days.
12-07-2012, 10:38 AM
My Honda CX500 m/cycle had a left handed bolt holding the fan blade onto the end of the crankshaft. As it is self tightening, the fan blade would never work its way off.
12-07-2012, 11:24 AM
I like that precession explanation. That is exactly what causes the orbital creep of the wheel stud on the nut and wheel as the load application changes while the wheel rotates.
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