Everyone in the HVAC/R trade uses some form of torch to braze or solder alloys together. So what is the proper way to handle an oxyacetylene torch? Turns out, there’s more than one right answer. Depending on which torch rig you use, the manufacturer’s manuals for operation may vary. 

Everyone (hopefully) knows a neutral flame on a torch tip is suitable for most applications. Sometimes a carburizing flame is useful for reducing oxidation. The only flame we all should avoid is the oxidizing flame. However, in order to achieve the correct flame, a technician must fully understand the type of torch tip they are using, and the application for which the torch is being used.

For example, a “rosebud” tip is a (often) a large high BTU tip, and may be too large for most residential applications. A lot of technicians will attempt to lower the fuel and oxygen pressures feeding the tip to reduce the temperature. However, the tip begins to starve due to a lack of adequate fuel/oxygen mixing, and the flame will back into the torch tip and coat the inside with a carbon coating, which can damage the tip and torch over time. On the other hand, a torch that is too small will never get hot enough for an application outside its design parameters.

So what tips are best? At what pressures must tips be set? There are many answers to these questions, and they all depend on the brand of equipment you use, and the application in which you work.

I had the opportunity to speak to Tim Thibodeaux from the Service Dept. at Victor Technologies, and with Matt Foster from Uniweld Products, Inc. Both confirmed that pressures are tip specific, and operating procedures are brand-dependent. For example, many technicians have been taught to shut off the FUEL first when shutting down the torch, but this contradicts manufacturer instructions.    

Uniweld states in their operation manual to shut off the OXYGEN first at the torch when following proper shutdown procedures. This is done to prevent flashback, or backfire. 

Uniweld Shut-down Prodedure

Victor Shut-Down Procedure

Victor, too, requires the operator to shut off the OXYGEN first at the tip, then the operator may shut off the fuel valve. The reasoning remains the same: to prevent backfire/flashback. So where does this “Shut off the fuel first” myth come from? Turns out, it’s been taught that way for decades, but not without reason.

I had the opportunity to speak with HVAC/R Training Legend Bill Johnson, one of the original authors of the Refrigeration and Air Conditioning Technologies (RACT) Manual, and we spoke extensively on the topic. The RACT Manual offers an alternative method of shutting down the torch rig. The textbook teaches to shut the FUEL off at the torch first. 

“Shut off the fuel gas (acetylene) valve at the torch first”
Refrigeration and Air Conditioning Technologies (8th Edition)

I asked Bill Johnson why that was, and he explained it was a way of protecting the technician over the tool. Starve the flame of its fuel first, and eliminate the flame right away. Also, this was the way he had been taught many years ago, and the first edition of the RACT Manual was published in 1987. Perhaps there was once a manufacturer operation manual that specified the “fuel off first ” method, but the procedures have since changed. This method is not without merit, as its intentions are pure.

With the proper PPE and setup procedures, following the manufacturers’ approved operation instructions should be standard across the trade. Some would argue that shutting the oxygen off first can cause the little carbon “bunnies” that are created when the acetylene pressure is low enough. This is easily rectified by changing the way you setup the torch to begin with keeping acetylene pressure at the tip specified level.

Uniweld Tip 17-1

Matt Foster from Uniweld mentioned several operating tips for torch tips and setting a flame. The most common torch tip he finds most technicians use is the Type 17-1, and is good for pipes with an inside diameter of up to 1”. The manufacturer’s design operating pressures for this tip is 5 acetylene/5 oxygen. Another common tip is the Rosebud Type 28-2; its operating pressures are 5-7acetylene/5-8 oxygen, and it is good for pipes with an inside diameter of up to 1-5/8”.    (Caveat: According to Matt, these published operating pressures may be even higher, as torch tip engineering changes over time, and the current catalog has not yet been updated. Therefore, when in doubt, take a look at the spec sheet that comes with the torch tip, or call the manufacturer to clear things up).

The Uniweld welding/brazing tip rated operating pressures can be found in their catalog here. The Victor welding/brazing tip rated operating pressure can be found here. As you can see, there is no one right answer when it comes to setting regulator pressure at the tanks. In schools, it is often taught to set fuel to 5psig at the regulator, and oxy at 10psig at the regulator. Some say the pressures should be the same at the regulator. The purpose for the pressure specifications is to ensure proper mixing of the gasses for the best quality flame, and to protect the torch rig from damage and compromised safety functions. So the answer to how to set your oxyacetylene regulator pressures is: it depends!

In other words…RTFM! (Read the FANTASTIC Manual) Hopefully, this clears up any confusion about torch rig operation and setup/shutdown procedures. Remember to ALWAYS wear proper PPE when dealing with any flame (eye protection, gloves, etc, and avoid polyester clothing), and follow industry best practices regarding safety.

— Kaleb