| AVS 56th International Symposium & Exhibition | |
| Vacuum Technology | Tuesday Sessions |
| Session VT-TuP |
| Session: | Vacuum Technology Posters and Student-Built Vacuum Systems Poster Competition |
| Presenter: | K. Arai, NMIJ/AIST, Japan |
| Authors: | K. Arai, NMIJ/AIST, Japan T. Tomita, NMIJ/AIST, Japan H. Akimichi, NMIJ/AIST, Japan M. Hirata, NMIJ/AIST, Japan |
| Correspondent: | Click to Email |
A static expansion system generates standard pressures for the calibration of a spinning rotor gauge and a capacitance diaphragm gauge. Valves are important parts for the system. All metal pneumatic valves are used for an automatic operation. However, the pneumatic valve closes so rapidly (<1 s) that the undesirable differential pressure between both sides of the valve is seemed to be induced by pushing gas. In order to clarify it, a test system consists of 45 m chamber and 3000ml chamber connected by the pneumatic valve was set up. The 13 Pa of differential pressure at the 100 kPa of line pressure was generated by closing the valve. The pressure decreased to 1.5 Pa by elongating the valve closing time, 150 s, by the control of the flow rate of the pneumatic line. However, the repeatability of the valve closing was not sufficient.
Pulse motor driven all metal valve was developed: (1) The motor drive part is attached to a commercial available valve, (2) A valve stem is driven by the pulse motor via a torque-limiter, springs, and a valve shaft, (3) The valve shaft position at closing the valve is always same by using the position sensor, (4) Springs are used to close the valve with the same torque, (5) To avoid the increase of the temperature of the valve body, the motor is operated only for the valve operation and 50 cm away from the body, (6) The torque-limiter is put between the motor and the shaft not to break the valve by the over torque.
The stem speed was controlled ranging from 0.1 to 0.008 mm/s (closing time: 25 ~ 300 s). The differential pressure could not be eliminated by slowing the stem speed. The smallest pressure was 1.4 Pa at the 100 kPa of the line pressure. Taking into account the pressure and the test chamber volume, 1.4 Pa is corresponding to the 0.0006 ml volume change of the valve. The mechanism of the undesirable differential pressure during the valve closing can be analyzed by measuring the detailed pressure change as a function of the time and the position of the stem.