Suppose we have a gas installation at 6 bars of pressure we have coupled a rotameter with a regulation tap , or a flow regulator with a Bourdon type meter.(non a pressure regulator)

When the solenoid valve on the winder closes, the entire length of tubing between the flow control valve and the winder is charged to the line pressure, and by experience we know that the pressure required in that section of pipe for 15 liters per minute of Flow rate is normally 0.4 bar.

Therefore at the initial time of the welding there is an excess flow rate and an undesirable consumption which will be equal to the volume inside the pipe multiplied by the difference between 0.4 bar And line pressure, in this case are 5.4 bar above atmospheric pressure. An 8mm diameter inner tube has a capacity of 50 cm3 per meter, with 20 meters in length being 1,000 cm3, or one liter, if we load it with 5.4 bars we have 5.4 liters at atmospheric pressure, each time We make a seam  WE TAKE ALMOST FIVE LITERS AND HALF OF GAS.

When  more longer and bigger the section of pipeline  ,  will be worse ….

The  shorter and frequent are the  seams , also worse …