Pneumatic cut-off valve of the pipe line of direction is what

What is the direction of pipe line of pneumatic cut-off valve system, the measurement of pipe jacking, before work should be dug pipe jacking pits, and then drew the ground pneumatic cut-off valve control pipe line to the pit wall and the piling nailed the midline, calibration line direction. When the center line of pipe jacking measurement, first in the tension between the two middle nail a thin line, online hang two pendant, two vertical ball attachment for pneumatic cut-off valve control direction of pipe line. To ensure the accuracy of the midline measurement, the distance between the two vertical lines as far away as possible. A wooden ruler in tube front horizontal, feet long is equal to or slightly less than pipe diameter, leveling of it with the level. Close to the two vertical line a thin line, extending to pipe the front-end wooden ruler, to see if it just by wooden ruler midpoint. The deviation shall not be more than 1. 5 cm, if excessive, should correct the position of the pipe.