In this instalment of Shop Class we’re continuing to draw on technical expertise from a variety of sources. They include Cal Shaw, a welding instructor who teaches at SIAST’s Palliser Campus, published text books and other training material. In this segment we’ll provide some basic tips on how to safely set up an oxyacetylene system in your shop.
After you’ve done your homework and decided what size of gas cylinders you need and you’ve purchased the appropriate torch kit to go with them, here is a step-by- step look at how to assemble everything.
First, give the gas cylinders a final inspection to make sure they weren’t damaged while bringing them home. Then firmly secure them in place. If you are permanently mounting them in one position inside the farm shop, make sure they are secured to a wall, post or other solidly-fixed object with a chain or strap to prevent them from being knocked over. A more practical installation is to secure them into a special hand cart designed to allow them to be wheeled to any location they’re needed.
But don’t just grab any old wheeled trolley and press it into service for this job. Carts used to carry gas cylinders must be very sturdy and stable. Special cylinder carts are designed so they cannot be easily knocked over.
A proper cart isn’t just to make sure you don’t scratch the paint on the cylinders. A hard blow to an acetylene cylinder can create a very dangerous situation. If the cylinder dents, it can create a pocket where the gas can collect outside the protection of the porous filler material and acetone that fills the cylinder along with the fuel gas (see last issue’s instalment for more on this). A damaged cylinder is an extreme explosion risk and should be immediately removed from service. And if a cylinder is ever knocked over or struck by another object that causes the valve to break off the top, you’ve just created an unmanned rocket that will use your shop for a launch pad.
Always use cylinders in an upright position only. Acetylene cylinders also contain acetone which can be forced out through the torch when the tank is lying horizontally. If an acetylene tank has been laid horizontally, even for a short time, let it stand for at least an hour before removing any gas from it. That will ensure no acetone escapes when you open the valve.
Once the cylinders are securely in place and settled, it’s time for the regulators to go on. But first, open (or “crack”) the valves momentarily to blow any debris out (although some sources discourage this and recommend using a clean, lint-free cloth to wipe them instead). If you use the “cracking” method, open and close the cylinder valves quickly, but do it carefully. Make sure you stand away from the expeled gas and don’t do this in the presence of any flame or fire hazard.
Be sure to look at the label on a cylinder to determine what it contains, don’t rely on its colour as an indicator. Oxygen cylinders are often green while acetylene is associated with black, but not always. Gas distributors are free to use any colour they like.
As a standard safety precaution to avoid mixing gases, fuel cylinders, like acetylene, use an opposite left-hand thread, while oxygen cylinders have a right-hand thread. This ensures the regulators go on the proper tanks. Use a properly-sized, open-end wrench, not an adjustable one, to tighten the regulators onto the tanks and not round off the connectors.
PURGE THE LINES
After installing flashback arrestors to the regulators, connect the hoses. But before connecting the torch, the lines should be purged. To do that, gently open the tank valve (always open tank valves slowly when regulators are attached, and ensure the regulator valves are closed by turning the adjuster counter-clockwise to prevent damage to the line pressure gauge), then briefly open the regulator valve by turning it clockwise. It, too, should be gently opened and closed.
Again, be careful to prevent a fire risk when allowing gases to escape. As a rule, hoses should be purged 10 seconds for every 100 feet of hose. Use the green hose to connect to the oxygen cylinder and the red one for acetylene.
Now attach the torch. All the left-hand-thread nuts used to connect the fuel (acetylene) line will have grooves in them to further help prevent confusing them with the oxygen connection.
CHECK FOR LEAKS
Before using any new cylinder or new part in the system, check all the connections for leaks. To do that, apply a little non-petroleumbased soap and water solution to each one. Then slowly build the line up to working pressure. If there is a leak, you’ll see bubbles at the problem connection. Shut off the gas flow, reconnect the joint and test again. Never use petroleumbased liquid for this job. And, need I say it, never use a cigarette lighter or other flame source either.
A final word about opening cylinder valves, be sure you do it correctly. There are two different types of valves in common usage. Oxygen tanks use a double-seated valve that can be opened by hand without a wrench. This type of valve must be opened all the way and set to avoid leaks. Never use it in the part-open position. Acetylene cylinder valves are different and should only be opened one to one-and-a-half turns. No more. Some types need to be opened with a wrench. If so, leave the wrench attached in case the system needs to be quickly shut down.