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When using acetylene, I know that it is important not to exceed the recommendedmaximumdraw off rate, but how do I know what this should be? Due to the special type of cylinder used to store acetylene, it is very important to ensure that the correct size of cylinder is selected for the process and never exceed the maximum draw off rate. Information about the recommended draw off rate is provided by the nozzle supplier but your gas supplier can also advise on this if necessary. Information about these recommendations is shown below.*
How important is it to purge the system before lighting up? This is the most important safety step. The system should be purged before every use, regardless of when it was last used. This is done by opening the acetylene cylinder and torch valve and adjusting the regulator to the correct pressure for the type of nozzle fitted. Allow the gas to flow while you’re setting the pressure but only in a well-ventilated area. This ensures the correct pressure when the system is in use and, more importantly, all the air has been purged out of the system. Next,
close the torch valve and the cylinder
is ready for use. The purging procedure should also be carried out on the oxygen cylinder.
Can you explain the reason why connections on an acetylene system always have a left-hand thread? This is for safety reasons. All flammable gases are connected using a nut with a left-hand thread and non-flammable gases are connected using a nut with a right-hand thread. This is to prevent the user from connecting the wrong equipment to the wrong cylinder.
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Paul Kendrick, Welding Applications Specialist at Air Products, offers some important safety advice for welders, when using acetylene and oxygen.
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EXPERT
* CYLINDER SIZE
10 LITRE CYLINDER
30 LITRE CYLINDER
50 LITRE CYLINDER
51 LITRE CYLINDER
58 LITRE CYLINDER
CYLINDER VOLUME M3
1.50 5.45 7.80 9.40 8.54
MAXIMUM CONSTANT WITHDRAWAL RATE M3
/HR 0.21 0.78 1.11 1.34 1.22
I occasionally use propane gas instead of acetylene, is it ok to use the same spark lighter for both? No, this is not recommended. When using any flammable gas, the lighting up process is high-risk and needs to be performed carefully, using the correct equipment. Both propane and propylene are less easily ignited than acetylene and a closed-cup spark lighter is usually preferred, which allows gas to build up in the cup, when igniting the gas. Acetylene has a much broader flammability range and is therefore much easier to ignite, so an open spark lighter should be used. Using the wrong spark lighter to ignite acetylene could cause an explosion in the cup or even a flash back. ■
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