Vacuum pressure proportional control valve

A vacuum pressure proportional control valve to be placed on a pipe connecting a reaction vessel and a vacuum pump to control vacuum pressure in the reaction vessel, the vacuum pressure proportional control valve comprising:

• a cylinder including a piston chamber;
• a piston housed in the piston chamber so that the piston makes reciprocal linear movement;
• a valve seat;
• a valve element configured to contact with or separate from the valve seat according to movement of the piston;
• a stopper member placed in the cylinder and including a leading end portion placed inside the piston chamber, the stopper member being configured to place the vacuum pressure proportional control valve in a fully-open state when the leading end portion contacts with the piston;
• and
• an adjusting unit configured to move the stopper member back and forth in a moving direction of the piston to adjust a position of the leading end portion.