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Oxy-Acetylene Cutting Torch Pressure Settings & Chart

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April 9, 2024

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One of the most widely used cutting tools is the oxy-fuel or oxy-acetylene cutting torch, commonly referred to as the blow torch. Using a cutting torch is easy in theory. Many people find it difficult to use, let alone make a good cut.

It’s the reason it’s so crucial to have the right settings. Most of them have no idea about the proper settings, particularly the working pressure. That is why the work they make is of poor quality.

Summary

The best pressure settings depend on the thickness of the metal that you’re working with. For example, for a metal that has a thickness of 0.125 inches, the pressure will be 20/25 oxygen (PSIG) and 35 Acetylene (PSIG). The description outlines some general recommendations not meant to replace the manufacturer’s recommendations.

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Oxy-Acetylene Cutting Torch Pressure Settings & Chart

Take a look at the oxy-acetylene pressure settings chart to understand what your torch should at for the most optimal results.

Multi-hole cutting

Fuel gas

The recommended setting is for the fuel gas regulator to be set at 10 PSIG and the oxygen regulator at 45 PSIG. This recommendation applies when cutting less than 1.5-inch steel using propane, propylene, or natural gas.

Oxy-Acetylene

The recommended setting for multi-hole cutting is the oxygen regulator at 40 PSIG, with the acetylene regulator setting at 10 PSIG. As with the previous recommendation, this applies to cutting less than 1.5 inches thick steel. The cutting tip oxy acetylene pressure will depend on the size. The manufacturer’s recommendations should always be followed.

Single-hole welding and brazing

Start looking for the stamped single-hole tip to see what number it has. Both the fuel-gas regulator and the oxygen regulator should have the indicated setting. This recommendation is not the case for injector-style options.

If you see that the tip has the number “5” on it, that is the number at which both the oxygen and fuel gas pressure should be set.

Unlike the portable blow torch, these different components must be correctly set up. Doing so ensures a proper operation that can result in quality work. It also minimizes the risks of accidents, especially flashbacks and explosions.

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Here are the important steps to follow when setting up an oxy-acetylene torch:

How To Set Up An Oxy Acetylene Cutting Torch Pressure

1. Ensure that the cylinders or tanks containing the two gases are properly secured and in an upright position.
   Use a cylinder cart if available. Ensure that they are properly fastened or chained to a sturdy place like a beam or wall. They should never be knocked down during operation or when not in use.
2. Remove any coverings placed on the valve of the cylinder or tank.
   But if protective covers were not used, remove any dust or debris that has settled inside the valves. It can cause the torch to malfunction. To do so, stand away from the valve’s opening or outlet (preferably on its opposite side). Turn the valve quickly about a quarter of the way and immediately close it. This quick release of gas will immediately blow away the dust or debris.
3. Connect the regulators to the valves but confirm that they have the same threads.
   If not, use an adaptor to connect them. They must have a completely tight and secure fit for safety and proper monitoring of the pressure settings. Manually screw them by hand as tight as possible, and use a wrench with a fixed opening to finish tightening them.
4. Attach the proper hoses if they are not connected to the respective regulators.If you have already used them before, connect them to the same tanks as before. The standard practice is to use green hoses for oxygen and red hoses for acetylene. Never apply any oil, grease, or any form of lubricant to the hoses. Especially make sure not to apply it on its ends.
5. Connect the torch handle to both of the hoses.Once securely attached, install the torch to the handle and manually tighten the nut. Check the valves on both the torch and its handle, as they must be closed before opening the valves of both cylinders.
6. Turn the valve of the oxygen tank or cylinder until it is fully open.Locate the regulator’s adjusting screw and turn it clockwise until the gauge shows that the pressure being released is between 40 to 60 psi.
7. For the acetylene cylinder, do a counterclockwise turn for the valve. Turn it only a quarter of the way.Turn the adjusting screw on the regulator until it releases gas, and the gauge shows 10 psi.
8. Find the oxygen valve and open it slightly to allow it to start flowing.Do the same for the acetylene valve but do not open it by more than 45 degrees or a 1/8 turn.
9. Do a leak test.Coat the valves and connections between the cylinder, hose, and regulators with a leak-test solution or a thin paste. It can be made by dissolving Ivory soap and using a clean brush for its application. A leak is present if you see any small bubbles on the coated surfaces after letting the solution sit for a few minutes.
10. If leaks are present, you must retighten or reattach connections first and do another leak test before lighting the torch.
11. Once no more leaks are present, follow the manufacturer’s instructions to light it up.

Remember to watch the flame as you use it. If it goes out as you’re working, stop and simply relight it. This occurrence is known as a backfire, and it happens when the torch itself and the metal being cut get into direct contact.

How to Light It

Lighting an acetylene torch is fairly easy, but you must follow the correct steps to do so. This mainly involves tinkering with the two valves of the cutting torch to get the right kind of flame. Also, make sure that both regulators show the right amounts of psi before lighting.

The following steps are the standard procedures but always check with the manufacturer for specific instructions:

1. Open the acetylene valve with a half-turn first before using friction or spark lighter to create a flame coming from the torch. Never use a match. There should be a one-inch gap between the tip of the torch and the flame coming out of the lighter.
   
   Using a match to light is risky. You may accidentally burn yourself once the flame comes out. Some also come with ignition devices, so manually lighting them up with a lighter is unnecessary.

2. Black smoke or soot may come out together with the flame. Wait until it disappears before slowly opening the oxygen valve. It being released will remove any yellow sections on the flame, which is essential for a neutral flame.
3. Adjust both valves to achieve a neutral flame. It must have a small, whitish or bright blue center and is clearly shaped like a cone.

When lighting it, make sure that the tip faces away from people or any flammable object to avoid any accident.

Tip Sizes & Tricks

Choosing the right tip size for your cutting torch will mainly depend on the thickness of the metal and the application. For instance, sheet metal will have very different requirements from thicker pieces. The different tips serve the same purpose. You must choose the correct tip to make it easier to achieve a quality result on the metal.

Each manufacturer has its recommendations for tip or nozzle sizes that depend on the thickness of the plate or metal. They also have different means of classifying the different tip sizes, but the standard practice is assigning a number. A low number indicates a small tip size, while a high number indicates a large tip size.

The thicker the metal, the bigger the nozzle or tip size will generally be required. This means a thin plate requires a tip with a small nozzle to make a precision cut. This kind of tip is insufficient for cutting through thick metal.

Tips for general use have more sizes available. This variation allows them to go through metals of varying thickness, from ¼ of an inch and up to 12 inches thick. Specialized tips have more limited sizes. Examples include angular ones.

Note that bigger tips with larger nozzle sizes will require more oxygen and acetylene to create a neutral flame and a slower speed to cut through metal cleanly.

How to Use It

To use it for cutting after setting up the equipment according to the outlined guide, pre-heat the metal. It is done in preparation for cutting. Do not press the lever when doing so, as the flame present is only hot enough for pre-heating. It’s not hot enough for cutting.

Do so at one of the edges or ends of the cut to be made, preferably at the most difficult section to cut. This will soften the metal to make it easier to do the work. Keep an eye on the pre-heated metal. Stop when the metal surface shows a bright cherry red color. This color indicates that the metal is ready for cutting.

Once the metal is soft enough, slowly press the lever to produce a suitable flame. Start at the pre-heated edge. Check if a cut has been made. Slowly make your way to the other edge of the metal at a consistent speed, and follow the mark you made on the metal.

Keep in mind that the metals are still hot afterward. Let them cool before touching them, even with gloved hands. Also, never lay down a lit-up torch on any surface. 

What is the Ratio Between the Two Gases?

A neutral flame is produced when a 1:1 ratio between the two gases. You need this kind of flame if you want a quality cut without affecting the metal’s properties. This is because equal amounts of these gases will produce carbon dioxide, which acts as a shielding gas. It then prevents the oxidation of the metal and gives you a clean cut.

Working Pressure – What Do You Set it At?

There should be equal amounts of acetylene and oxygen to produce a neutral flame. You must observe the right pressure settings when working with this piece of equipment. It will depend on the work that you’re doing. Note that the ratio of oxygen is different from the pressure required. This means that the two should not have equal psi readings, which is very important.

In general, oxygen must have a higher pressure setting for the tool to work optimally. The actual cutting torch setting will depend on the tip used and manufacturer recommendations. But as a rule, more pressure for both gas is needed for bigger-sized cutting tips. It makes sense, as it requires more power to work on thicker pieces of metal.

Suppose the recommended working pressure settings are not indicated. Safe numbers are 40 psi for oxygen and 10 psi for acetylene, regardless of tip size. Simply adjust them until you get a neutral flame. Pay close attention to the pressure to prevent it from exceeding the limit. Ensure that you check to see if the manufacturer has indicated anything specific regarding the two types of gas pressure. When that’s the case, those settings should always be followed.

What is the Maximum Working Pressure?

The maximum working pressure for acetylene gas when using a cutting torch is 15 psi or 103.4 kPa. If the pressure goes beyond that, it gets unstable and becomes dangerous. It is a flammable gas. When it becomes unstable, it is at risk of spontaneously combusting. Raw gas can cause an explosion even with a slight shock.

Fortunately, this risk is minimized because it is stored inside cylinders or tanks and is dissolved in acetone. Liquid acetone stabilizes this gas to prevent it from combusting. Also, the cylinders themselves are laced with acetone. It makes it possible to transport or move around the gas tank or cylinder safely.

If the acetylene pressure exceeds 15 psi, it will use up the acetone present in the cylinder to be stable. While it has a positive effect on acetylene, acetone negatively affects the components of your system. It can cause damage or deterioration to any plastic or rubber parts, affecting the quality of the work. This will eventually cause the regulator to fail, stopping the entire system. This failure is a sign that the acetone present is nearly depleted. What mostly remains in the cylinder is dangerous raw acetylene.

The worst-case scenario is that the rubber hose will deteriorate before the regulator fails because it has drawn up so much acetone. And when this happens, an explosion is likely to occur.

What Do You Turn Off First?

Turning off the cutting torch should follow the right order for safe operation, particularly involving oxygen and acetylene. However, this is a point of contention for many. Some believe that the acetylene valve must be switched off first, while others advocate turning off the oxygen supply first.

The consensus among manufacturers is that the oxygen should be switched off first. Follow it by switching off the acetylene, not the other way around. This allows any soot that settled on the torch to be blown away by the acetylene. A buildup of soot can prevent the fuel valve from properly being sealed off, causing it to leak.

This method also allows you to see if any leaking is present before you completely switch off the cylinders. If there is a leak, a small flame will remain after turning off both gases. Detecting a possible leak is crucial to avoiding an explosion.

Interchanging them is possible, but hearing a loud bang is more likely if you switch off acetylene before oxygen. This pop indicates a mini-flashback. When this happens, you must immediately turn off the oxygen. Even mini-flashbacks can be potentially dangerous.

We hope this article has helped you!

FAQ

What are the two types of cutting torches?

There are both oxy-acetylene torches or blow torches and plasma cutter torches in the market. Both have their pros and cons and qualities that make them unique. Electrical energy is added to neutral gas in a plasma cutter, and ignition comes from mixing an electrode and a nozzle.

The result is plasma gas used to cut through metal and other substances. Plasma cutters can cut through more metals than other types of torches. They can even prove to be more accurate in cutting. It doesn’t require preheating and thus saves on time too.
In an oxy-acetylene torch, oxygen and fuel gas are used to heat the metal to a certain ignition temperature. That is when the cutting can begin. While oxy torches have the advantage of being portable, they cannot cut through certain metals. These include:

• copper
• stainless steel
• and aluminum.

They do not oxidize easily.

Can you use propane?

If you’re thinking, “can you use any other gas in your store when you run out of acetylene?” Here’s your answer. You can use propane in your torch and even find that it’s cheaper to use than acetylene. But if you want something that burns quickly, acetylene is hotter than propane and can be more effective for your task. But keep in mind that you will have to wait longer for the flame to ignite the metal as propane has less heating power. As well as this, propane will not be able to weld certain metals because it cannot be made to turn into a neutral flame.

What should it be set at?

If you’re multi-hole cutting, you need the oxygen set at 40psi and the fuel at 10psi. Always check your equipment manual before you set your torch. Acetylene pressure must not exceed 9psi unless the tool is designed for it. It’s also dangerous to use acetylene above 15 psi as it becomes spontaneous and highly combustible in this setting.

Here’s a crucial question, especially when you’re just getting started with your blow torch. You will need expert guidance and safety procedures to handle the torch correctly. Here’s the full procedure below.