Backing channel pressure regulation

When welding with backing gas, you have to regulate the pressure in the pipe so that the root bead is formed cleanly. Too much pressure blows up the weld, too little pressure lets it sag or sink. So you need a regulator valve that keeps the gas pressure constant, and you have to adjust the pressure to the pipe diameter and wall thickness. If you don't get that under control, you'll get pores, cracks, or an uneven weld shape. Just set the pressure so that the root is fully penetrated from the inside without the weld bulging.