The last step in lighting a positive-pressure oxyacetylene cutting torch involves

The last step in lighting a positive-pressure oxyacetylene cutting torch involves

• A. Opening the torch acetylene valve to approximately 1/16 to 1/8 turn
• B. Turning on the acetylene until most the smoke clears from the flame
• C. Opening the cutting oxygen valve and adjusting the working pressure to obtain neutral preheat flames
• D. None of the above

Answer: (C)

The key idea is to finalize the flame by balancing the fuel and the oxidizer so you have a neutral preheat flame before starting to cut. In a positive‑pressure oxyacetylene torch, the cutting oxygen valve controls the oxygen used for both preheating and cutting. Opening that valve and setting the pressures so that the flame is neutral—neither too fuel rich nor too oxygen rich—gives you clean heat for preheating the steel and prepares you to start the cut safely. A neutral flame has a well-defined inner cone and a balanced color, which minimizes carbon buildup and ensures consistent heat. The other steps you might perform earlier—like opening the acetylene valve a bit to light the torch or waiting for smoke to clear—are part of lighting, but they don’t guarantee the correct, controlled preheat flame.

The key idea is to finalize the flame by balancing the fuel and the oxidizer so you have a neutral preheat flame before starting to cut. In a positive‑pressure oxyacetylene torch, the cutting oxygen valve controls the oxygen used for both preheating and cutting. Opening that valve and setting the pressures so that the flame is neutral—neither too fuel rich nor too oxygen rich—gives you clean heat for preheating the steel and prepares you to start the cut safely. A neutral flame has a well-defined inner cone and a balanced color, which minimizes carbon buildup and ensures consistent heat.

The other steps you might perform earlier—like opening the acetylene valve a bit to light the torch or waiting for smoke to clear—are part of lighting, but they don’t guarantee the correct, controlled preheat flame.