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How To Cut With Oxyacetylene, Part 2

If you don’t already have an oxyacetylene system in your farm shop, here is a look at what you need to know before the spending money to buy one. In this segment we’re drawing 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, training material and Jennifer Fabian, an Occupational Health and Safety official, to help you make the right choices.


First, you need to decide if you want to use acetylene as the fuel gas in your system. You do have other options. MAPP and propane can also do the job, just not as efficiently as acetylene. These other fuels have a lower flame temperature, which means you may be limited in the maximum thickness of steel you can cut. Although they will likely handle any job around the farm without any trouble, you’ll just need to move the torch a little slower when cutting. And you may have better access to these other fuels, saving time and effort each time a cylinder needs refilling.

You also need to decide which gas you’ll be using before buying the torch kit. Different fuel gases require dedicated torches that are designed specifically for them. Don’t try and use an incorrect fuel gas-torch combination.


You’ll find a lot of different torch models to choose from. Prices can range from a few hundred to a few thousand dollars. You won’t need to spend top dollar on a torch kit for just occasional use. The expensive systems are generally designed for professional applications that see a lot of demanding use.

If you decide to go with acetylene, get a cylinder with enough capacity for the jobs you need to do. In most cases, you can only rent gas cylinders and distributors offer several sizes. When you buy your torch system, you’ll find out what gas flow rate you need for various jobs. Each torch manufacturer provides a chart with their kits that explains what tip and pressure setting combinations are required for cutting different thicknesses. The charts also specify the corresponding rate of acetylene and oxygen flow needed from the cylinders in litres per minute.

Why is knowing the flow rate important? Because you can only safely draw 1/7 of the vol- ume out of an acetylene tank per hour. If the tank capacity is too small for the work you’re doing, you will exceed its capacity.

To understand the significance of that, you need to know an acetylene tank is not a hollow cylinder. It is filled with a porous substance that is saturated with acetone. This allows acetylene to be stored at high pressures that would otherwise cause it to explode. It cannot be safely stored above 15 PSI without acetone. Normal cylinder pressures are approximately 240 PSI in a medium sized tank

When removing acetylene from the cylinder, it requires time to separate from the acetone and flow out properly. Drawing it out too quickly will pull out some acetone. Aside from causing trouble in the torch, the reduced acetone volume remaining in the cylinder may be inadequate to keep the acetylene stable. This is also the reason acetylene cylinders can only be used in the upright position. Laying them horizontally when the valve is open allows the acetone to flow out with the gas.


Having the gas cylinders mobile in a shop makes them convenient to use, so they are best mounted on a wheeled cart. But don’t just buy any cheap hand-truck version and expect it to work. Dedicated gas cylinder carts are designed to be extremely stable, preventing them from falling over. If an acetylene cylinder falls and dents, it becomes dangerous. If a dent creates a gap between the cylinder wall and the porous filling, it can allow pure acetylene to accumulate unprotected at

Prices can range from a few hundred to a few thousand dollars. You won’t need to spend top dollar on a torch kit for just occasional use.

high pressure. It then becomes sensitive to shocks which could cause it to explode.


When storing tanks unused for any length of time, remove the regulators and install the screw-on valve caps. They protect the valves from accidental damage, which can cause leaks. Acetylene can be explosive in the atmosphere at concentrations ranging from as low as two per cent to as high as 80. So you don’t want any small, undetected leaks.

That brings up another requirement. If you have paid employees working in your farm shop, you’ll need to provide them with information about what dangerous chemicals stored there and how to react in an emergency, in accordance with federal WHIMIS regulations.

According to Jennifer Fabian, director of safety services for Occupational Health and Safety in Saskatchewan, farmers are not exempt from these regulations.

Everyone with an oxyacetylene system will have to transport gas cylinders at some time. So here are some musts to ensure the job is done safely.

1) Gas cylinders are never completely empty, so always be alert to the risk of leakage. To minimize the risk, never transport them in a closed area, like a car trunk, and never in the passenger compartment. On a hot, sunny day, keeping a cylinder in a trunk or inside a vehicle can raise its temperature to a dangerous level creating an explosion risk.

And they also have a duty to provide adequate training to employees using oxyacetylene systems.

The same is likely to be the case in other provinces, too. “We’re all pretty much consistent in our approach,” she says. For more information on farm

2) Cylinders should always be firmly secured and, ideally, transported in an upright position. Ensure the safety cap over the valve is in place. If you’ve transported an acetylene cylinder horizontally, stand it upright and allow at least one hour to pass before trying to draw any gas from it.

3) After loading a cylinder in a vehicle, take a direct route home. Don’t make any side trips or unnecessary stops. Unload it as soon as you get there.

owners’ safety obligations in Saskatchewan, see www.lrws.

Next issue we’ll look at how to put an oxyacetylene system together the right way.


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About the author


Scott Garvey

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.



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