Gas pressure feed device

1. A gas pressure feed device comprising:

a compression device for compressing gas supplied from an upstream process and sending the gas to a downstream process;

a shut off device provided downstream from the compression device for shutting off the gas heading toward the downstream process; and

a recirculation device for recirculating the gas shut off by the shut off device to the upstream process of the compression device, wherein

the shut off device includes

a first port on a primary side for introducing the gas from the compression device,

a second port on a secondary side for sending the gas to the downstream process,

a third port on the secondary side for sending the gas to the recirculation device, and

a switching device for switching the gas heading toward the secondary side to either the second port or the third port, wherein

the shut off device comprises a three-way valve having a case-shaped valve main framework, a valve port (“inner port”) supported such that a secondary side thereof is movable between positions of the second port and the third port in the valve main framework, and a driving device for driving the valve port (“inner port”),

the valve port is provided with a first communication portion communicable with the first port, a second communication portion communicable with at least one of the second port and the third port, and a gas flow portion for allowing gas to flow from the first communication portion to the second communication portion, and wherein

the gas flow portion decreases in diameter from the first communication portion to a middle position where a cross sectional area of the gas flow passage is equal to or greater than an opening area of a flow passage at the first port, and the diameter of the gas flow portion increases in diameter from the middle position and toward the second communication portion, and wherein the diameter of the gas flow diameter changes continuously and smoothly from the first communication portion to the second communication portion.

2. The gas pressure feed device according to claim 1 , wherein in an intermediate stage of switching by the switching device, the shut off device continues to send the gas toward at least one of the second port and the third port.

3. The gas pressure feed device according to claim 2 , wherein the valve main framework is provided with the first port, the second port, and the third port, wherein the switching device is constituted by the valve port (“inner port”) and the driving device and wherein movement of the valve port (“inner port”) by the driving device switches between a first position in which the first communication portion communicates with the first port and the second communication portion communicates with the second port and a second position in which the first communication portion communicates with the first port and the second communication portion transports with the third port.

4. The gas pressure feed device according to claim 3 , wherein the valve port (“inner port”) is formed in a spherical shape and a secondary side thereof is rotationally supported between the positions of the second port and the third port in the valve main framework, wherein the first communication portion and the second communication portion are positioned oppositely in a radial direction of the valve port, and the gas flow portion is formed passing through the valve port (“inner port”), wherein the first communication portion has an opening area enveloping the first port in a movement range caused by rotation of the valve port (“inner port”), and wherein the second communication portion is configured to have an opening area in which a total of a cross sectional area of a flow passage at the second port and a cross sectional area of a flow passage at the third port during switching between the first position and the second position caused by the rotation of the valve port (“inner port”) is equal more than half of a cross sectional area of a flow passage at the first port.

5. The gas pressure feed device according to claim 1 , wherein the valve main framework is provided with the first port, the second port, and the third port, wherein the switching device is constituted by the valve port (“inner port”) and the driving device and wherein movement of the valve port (“inner port”) by the driving device switches between a first position in which the first communication portion communicates with the first port and the second communication portion communicates with the second port and a second position in which the first communication portion communicates with the first port and the second communication portion transports with the third port.

6. The gas pressure feed device according to claim 5 , wherein the valve port (“inner port”) is formed in a spherical shape and a secondary side thereof is rotationally supported between the positions of the second port and the third port in the valve main framework, wherein the first communication portion and the second communication portion are positioned oppositely in a radial direction of the valve port, and the gas flow portion is formed passing through the valve port (“inner port”), wherein the first communication portion has an opening area enveloping the first port in a movement range caused by rotation of the valve port (“inner port”), and wherein the second communication portion is configured to have an opening area in which a cross sectional area of a flow passage at the second port and a cross sectional area of a flow passage at the third port during switching between the first position and the second position caused by the rotation of the valve port (“inner port”) is equal to more than half a cross sectional area of a flow passage at the first port.