What should the pressure of acetylene gas be when actually welding?

The optimum pressure for acetylene gas when welding is generally around 5 psi. This pressure is considered ideal because it allows for a stable flame that is necessary for effective welding. At this pressure, the gas provides a sufficiently hot and controllable flame while minimizing the risk of flashback, which can occur if the pressure is too high.

Additionally, operating at around 5 psi ensures that the acetylene remains in a dissolved state within the cylinder, preventing it from becoming unstable. Higher pressures can lead to an incomplete combustion and a less efficient welding process, potentially affecting the quality of the weld joint. Therefore, maintaining the pressure around 5 psi is crucial for achieving optimal welding results.