and tighten the left-hand nut. Connect the oxygen pressure  regulator to the oxygen cylinder and tighten the right-hand  nut. The connection fittings are brass and do not require a lot  of torque to prevent them from leaking. At this time, check  to ensure the adjusting screw on each pressure regulator is  backed out by turning counterclockwise until it turns freely.  Connect the red hose with the left-hand threads to the  acetylene pressure regulator and the green hose with the  right-hand threads to the oxygen pressure regulator. This  is the location, between the regulator and hose, in which  flashback arrestors should be installed. Again, because the  fittings are brass and easily damaged, tighten only enough  to prevent leakage.  Stand off to the side away from the face of the gauges. Now,  very slowly open the oxygen cylinder valve and read the  cylinder gauge to check the contents in the tank. The oxygen  cylinder shutoff valve has a double seat valve and should be  opened fully against its stop to seat the valve and prevent a  leak. The acetylene cylinder shutoff valve should be slowly  opened just enough to get the cylinder pressure reading on  the regulator and then one half of a turn more. This allows a  quick shutoff, if needed.  NOTE: As a recommended safety practice, the cylinders  should not be depleted in content below 20 psi. This prevents  the possible reverse flow of gas from the opposite tank. Both hoses should be blown out before attaching to the torch.  This is accomplished for each cylinder by turning the pressure  adjusting screw in (clockwise) until the gas escapes, and then  quickly backing the screw out (counterclockwise) to shut  off the flow. This should be done in a well ventilated open  space, free from sparks, flames, or other sources of ignition.  Connect the red hose with the left-hand thread connector  nut to the left-hand thread fitting on the torch. Connect the  green hose with the right-hand thread connector nut to the  right-hand thread fitting on the torch. Close the valves on the  torch handle and check all connections for leaks as follows: NOTE: Acetylene is limited to a maximum continuous  withdrawal rate of one-seventh of the cylinder’s rated  capacity when full. For example, an acetylene cylinder that  has a capacity of 330 cubic feet has a maximum withdrawal  of 47 cubic feet per hour. This is determined by dividing 330  The following provides some recommended procedures to  guard against overheating and flashbacks: All fuel cylinders have a limited capacity to deliver gas to  the tip. That capacity is further limited by the gas contents  remaining in the cylinder and the temperature of the cylinder. Starvation occurs if torch tips are operated at less than  the required volume of gas, leading to tip overheating  and possible flashbacks. Incorrect tip size and  obstructed tip orifices can also cause overheating and/or  flashback conditions.  Welding tips have one hole and cutting tips have a number  of holes. The cutting tip has one large hole in the center for  the cutting oxygen and a number of smaller holes around  it that supply fuel, gas, and oxygen for the preheating  flame. The selection of the tip size is very important, not  only for the quality of the weld and/or the efficiency of the  cutting process, but for the overall operation of the welding  equipment and safety of the personnel using it.  Welding and cutting tips are available in a variety of sizes  for almost any job, and are identified by number. The higher  the number is, the bigger the hole in the tip is allowing more  heat to be directed onto the metal and allowing thicker metal  to be welded or cut. •  A general tightening of all connections should fix the  leak. Repeat a check of the system.  •  If a leak is still indicated by a loss in working pressure,  a mixture of soapy water on all the connections reveals  the source of the leak. Never check for a leak with a  flame because a serious explosion could occur. Select the Tip Size Hoses Connecting Torch •  Turn in the adjusting screw on the oxygen pressure  regulator until the working pressure indicates 10 psi.  Turn in the adjusting screw on the acetylene pressure  regulator until the working pressure indicates 5 psi. •  Back out both adjusting screws on the regulators and  verify that the working pressure remains steady. If it  drops and pressure is lost, a leak is indicated between  the regulator and the torch. •  Refer to the manufacturer’s recommendations for tip  size based on the metal’s thickness. •  Use the recommended gas pressure settings for the tip  size being used. •  Provide the correct volume of gas as recommended  for each tip size. •  Do not use an excessively long hose, one with multiple  splices, or one that may be too small in diameter and  restrict the flow of gas.  5-11