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February 10, 2020

What is Gas Welding?

Welding is a method of joining metal parts and structures by fusion with or without the use of a welding rod. Every airplane depends on welding for adding strength to some parts of its structure.

Aircraft mechanics master the use of welding apparatuses for heating and tacking.

Two general types of welding are gas and electric.

Gas welding is generally used more in the construction and maintenance of aircrafts.

What is a Fuel Gas Cylinder Welding System?

Gas welding using oxygen and acetylene tanks is generally known as a fuel gas cylinder welding system. Other fuel gases besides acetylene are also used for different types of welding, but the oxyacetylene welding system is the most common.

Components of a Portable Oxyacetylene Welding System

A portable oxyacetylene welding system has the following components:

  • Cart: used to carry the cylinders around and prevent them from tipping over
  • Cylinders: one for oxygen and one for acetylene
  • Regulators: used to control the flow of gas from the cylinders
  • Hoses: used to connect the regulators to the torch
  • Torch: used for controlling the flame for welding

Oxygen Cylinder

Note that the oxygen cylinders have about 2200 psi pressure when they’re full. They’re a potential bomb. If not handled properly, they can be extremely dangerous.

Acetylene Cylinder

Acetylene cylinders contain liquid acetone and acetylene. Acetone absorbs 25 times its own weight in acetylene, making the acetylene stable in the cylinder.

Why should it be used standing upright?

If the cylinder is laid down and the acetylene is attempted to be drawn off, it will pull off liquid acetone and this will likely result in a fire. For the same reason, it is advised to keep the acetylene cylinder standing for at least an hour before any acetylene is drawn from it.

Securing the gas cylinders

Install oxygen and acetylene tanks in position. Secure the cylinders to the cart firmly using a chain or any other locking mechanism to prevent the cylinders from tipping over and being damaged while in use.

Safety cap

The top cylinder valve is covered with a safety cap, which must be on when the cylinder isn't in use. Also, make sure that the safety cap is on anytime the cylinder is moved or handled.

To prepare the oxyacetylene welding system, remove the safety caps off the cylinders.

Preparing the regulators

The next step is to put the regulators onto the cylinder valves.

Open the cylinder valve for an instant to blow any dirt or other foreign material out of the valve before putting the regulator on the cylinder valve.

Inspect the oxygen regulator. Make sure that the seat of the regulator is clean and free of dirt and damage.

Seat the regulator on the valve correctly. Otherwise, it will create a leak and may even be dangerous.

Secure/turn the regulator knob enough to prevent any leakage.

Do not apply oil for securing/seating the regulator.

Oil in the presence of high-pressure oxygen can be explosive. This can damage the regulator and may cause fire or explosion.

Repeat the process for the acetylene tank by removing the safety cap and preparing it for putting the regulator on.

Open the cylinder valve for an instant to clear the cylinder. Make sure that the valve doesn't have any foreign material in it.

Fuel gas cylinders like acetylene have left-hand threads, so they cannot be attached to a non-fuel gas cylinder like the oxygen tank.


Make sure that the hoses are clean and free of foreign material and damage.

Oxygen hoses are always green and are attached to the oxygen regulator.

Acetylene hoses are generally red. The acetylene hose nut will be left-handed too. It is also left-handed where it fits onto the torch.

What would happen if there was some foreign material and you inadvertently went ahead and connected the hose?

This can potentially cause the material to be blown into the regulator and damage the calibration on the regulator.

Connect the hose to the torch

Install the oxygen hose onto the torch. It has right-handed threads, whereas the acetylene hose has left-handed threads, so it will never be possible to connect to the wrong hose.

Tighten the hoses enough to prevent any leakages on the torch. Tightening the hose too much may damage the seat and pull threads out of the nut.

Make sure that the torch valves are off. Check the adjusting screws on the regulator and make sure that they don't have any tension in them. Then, open the cylinders and apply the pressure to the regulator.

If you watch the gauge carefully, the pressure gauge will come up slowly.

It’s important to open the cylinder slowly so the calibration of the gauge isn't damaged.

Open the oxygen cylinder all the way. It should be tight against the upper seat.

Because it is a high-pressure valve, it has a double seat in it. It will leak if you don't open the oxygen tank all the way.

The regulator gauge on the right-hand side will show the pressure rising; this is the cylinder pressure gauge. The one on the left doesn't have pressure until you turn the adjusting screws on the regulator.

Next, do the same for the acetylene cylinder.

Open acetylene cylinder to the point where you can offer unrestricted flow.

Turn on the acetylene cylinder slowly and let the pressure come up. Open the acetylene at about 1/4 to 1/2 of the turn, not all the way.

Why does acetylene only have to open a quarter to a half?

Acetylene is the fuel gas here, it’s important that you can turn it off in case of fire. If it's opened too much, you may not be able to turn it off quickly.

Check the cylinders to make sure the regulators are showing the correct values in the cylinder and torch gauges.

Adjust the regulator of the oxygen tank to adjust the working cylinder gauge to the desired pressure.

Do the same for the acetylene regulator. Acetylene is not used at or above 15 psi. It is usually indicated by a red line following the 15 psi on the regulator gauge. Using more than 15 psi may cause an explosion.

Inspect for leakages using soapy water

At this point, soapy water may be used to inspect for leaks.

Check all connections in the system. Tighten any connections where leaks are found and recheck to make sure it isn't leaking anymore.

The complete operation takes 5 - 10 minutes if there are no problems.

If you don't fix the leak, you will waste fuel gas, and it can lead to other dangerous complications.

Finally, inspect the torch.

Now you are ready to weld.

Does this need to be checked every day?

Check when you undo a hose or take off a regulator which needs to be reinstalled or replaced.

The torch manufacturer may recommend values for the working pressures of both oxygen and acetylene, for instance, 4 psi for oxygen and 4 psi for acetylene.

Using the fuel gas welding system

Turn on some acetylene by rotating the knob on the torch; light it with a striker.

A match is never used to light the torch. When the acetylene flows from the tip, it accumulates and if you light it using a match, you will get flash flame for an instant, and it's possible to be burned badly.

Next, turn on the oxygen.

Preparation for shutting system down

Turn off the oxygen valve first, then the acetylene valve.

When the cylinder valve is closed, open the torch valves and allow the pressure to bleed off the system.

The pressure on both gauges of the oxygen valve regulator will drop to zero. Repeat the process for acetylene.

Remove the regulator. This will ease the diaphragm and allows the regulator to stay in calibration.

The system is now ready for storage. It is completely shut down.

Acorn Welding is your one-stop shop for quality aircraft exhaust and engine mounts. Serving customers around the world, we are Canada's largest aircraft exhaust and engine mounts repair company and the world's largest radial and vintage aircraft exhaust repair company. Contact Acorn Welding today regarding any inquiries you may have.