| 摘要 |
PURPOSE:To adjust the pressure in a vacuum tank automatically and finely to a desired value by providing a constant throttle at the intake side of the vacuum tank and adjusting the discharge side with a variable-conductance valve having a special shape. CONSTITUTION:A variable-leak valve 5 set to allow gas of a constant quantity to flow into a tank from a gas cylinder 4 is connected to the intake side pipe of a vacuum tank 1, and a variable-conductance valve 6 as a discharge valve and a vacuum pump 2 are connected to the discharge side pipe. When the piston valve 13 of the variable valve 6 retreats from a valve seat by means of a drive motor, the cross-sectional area of a key-type passage (a1, a2, a3) formed by the conical piston peripheral surface and the cone-shaped surface of the valve seat tends to increase gradually. It was found that the gas flow through such a fluid passage was nearly proportional to the piston displacement within a certain range of the piston stroke. Therefore, the degree of vacuum in the vacuum tank 1 can be automatically adjusted and maintained at a desired value by finaly adjusting the displacement quantity of the piston by means of the PID control of the drive motor. |
