Valve mounted above the Vacuumpump. . Open valve. When the solenoid valve is energized (simultaneously with the vacuum pump), the atmospheric vent port is closed, and the channel of the body and the top of the piston are opened. If the pressure at the vacuum pump side decreases, the pressure at the top of the piston also decreases via the channels of the shaft and the body. The pressure difference generated at that time makes the piston move upward. If the pressure decreases more, the channel of the shaft is closed, but the pressure at the top of the piston decreases much more via the channel of the body, and it opens the valve. . Close valve. When energizing to the solenoid valve is stopped (simultaneously with the vacuum pump), the channel of the body is closed, and the atmospheric vent port and the top of the piston are opened. As the top of the piston gets atmospheric pressure via the atmospheric vent port, the valve is closed as the piston moves downward with the built-in spring. When the piston moves downward further, the channel of the shaft is opened, and it leads atmosphere to the vacuum pump side.