Pressure control butterfly valve with opening/closing mechanism

1. A pressure control butterfly valve comprising:

a valve disc rotatable in a vertical direction relative to a flow passage in a body;

a seat ring reciprocating in a direction of the flow passage to allow a valve seat seal part to abut on and separate from the valve disc;

a valve opening/closing mechanism provided with an airflow path to which air is supplied in a direction of separating the seat ring from the valve disc and with a spring for biasing the seat ring toward the valve disc; and

an electromagnetic valve for supplying the air from a pump to the airflow path and stopping the supply of the air and an electropneumatic regulator which are connected in parallel;

wherein the valve opening/closing mechanism is for nonslidably rotating the valve disc from which the seat ring has been separated by supply of air to the airflow path and for allowing the seat ring to abut on and separate from the valve disc by means of the supply of air to the airflow path and a biasing force of the spring when the valve disc has been rotated to a valve-closed state, thereby controlling pressure in the flow passage.

2. A pressure control butterfly valve according to claim 1 , further comprising a stepping motor connected to the valve disc for transmission of rotation and a controller connected to the stepping motor and to the electropneumatic regulator, wherein the controller comprises a valve disc control section for controlling rotation of the stepping motor to control a number of rotations of the valve disc and an air control section for controlling output pressure applied to the airflow path by the electropneumatic regulator to control a degree of opening of the seat ring.

3. A pressure control butterfly valve according to claim 1 , wherein the valve disc has a rotating shaft eccentric from a center of the valve disc and a center of the flow passage.

4. A pressure control butterfly valve comprising:

a valve disc rotatable in a vertical direction relative to a flow passage in a body;

a seat ring reciprocating in a direction of the flow passage to allow a valve seat seal part to abut on and separate from the valve disc; and

a valve opening/closing mechanism provided with an airflow path to which air is supplied in a direction of separating the seat ring from the valve disc and with a spring for biasing the seat ring toward the valve disc;

wherein the valve opening/closing mechanism is for nonslidably rotating the valve disc from which the seat ring has been separated by supply of air to the airflow path and for allowing the seat ring to abut on and separate from the valve disc by means of the supply of air to the airflow path and a biasing force of the spring when the valve disc has been rotated to a valve-closed state, thereby controlling pressure in the flow passage;

wherein the valve disc is provided on a side of contact with the valve seat seal part with an O-ring, and the valve seat seal part is formed on an inner circumferential side of the seat ring into a tapered or circular arc shape gently enlarged in diameter from an inside diameter side toward an outside diameter side.

5. A pressure control butterfly valve according to claim 1 , wherein the body has a stopper attached thereto for regulating to a prescribed position the seat ring that has moved by supply of air to the airflow path.

6. A pressure control butterfly valve comprising:

a valve disc rotatable in a vertical direction relative to a flow passage in a body;

a seat ring reciprocating in a direction of the flow passage to allow a valve seat seal pad to abut on and separate from the valve disc; and

a valve opening/closing mechanism provided with an airflow path to which air is supplied in a direction of separating the seat ring from the valve disc and with a spring for biasing the seat ring toward the valve disc;

wherein the valve opening/closing mechanism is for nonslidably rotating the valve disc from which the seat ring has been separated by supply of air to the airflow path and for allowing the seat ring to abut on and separate from the valve disc by means of the supply of air to the airflow path and a biasing force of the spring when the valve disc has been rotated to a valve-closed state, thereby controlling pressure in the flow passage;

wherein the body has a stopper attached thereto for regulating to a prescribed position the seat ring that has moved by supply of air to the airflow path;

wherein the stopper comprises a columnar pin and a cam that is eccentric from the pin and has a cam face on which the seat ring abuts.