1. A gate valve, comprising: a first valve plate having a valve opening; a second valve plate connected to said first valve plate via an expandable body; and an actuator provided between said first valve plate and said second valve plate, wherein said first valve plate and said second valve plate are both operative to be moved by the actuator away from each other or toward each other.
2. A gate valve according to claim 1, wherein said first valve plate is provided with a valve rod.
3. A gate valve according to claim 1, wherein said second valve plate is provided with a valve rod.
4. A gate valve according to claim 1, wherein a valve rod is located at the center of the expandable body in the axial direction.
5. A gate valve according to claim 1, wherein said actuator comprises an air cylinder.
6. A gate valve according to claim 1, wherein said actuator is surrounded by dustproof bellows provided between the valve plates.
7. A gate valve according to claim 5, wherein said air cylinder comprises: a piston provided at the valve plates; a piston rod; Resilient Seated Gate Valvesand a cylinder, wherein a pressure medium is supplied to a space formed between the piston and the cylinder.
8. A gate valve according to claim 1, wherein said first valve plate is provided with first sealing member.
9. A gate valve according to claim 1, further comprising: a valve casing for enclosing said valve plates in such a manner that said valve plates can freely move; a first valve seat, with which first sealing member come into contact, formed in a first opening of the valve casing; and a first stopper, with which a second valve plate comes into contact, formed in a second opening of the valve casing.
10. A gate valve according to claim 1,Gate Valves further comprising: a valve casing for enclosing said valve plates in such a manner that said valve plates can freely move; a first sealing member, with which said first valve plate comes into contact, formed in the first opening of the valve casing; and a first stopper, with which said second valve plate comes into contact, formed in the second opening of the valve casing.
11. A gate valve according to claim 1, further comprising: a valve casing for enclosing said valve plates in such a manner that said valve plates can freely move; a first valve seat, with which the first sealing member comes into contact, formed in the first opening of the valve casing; and a second stopper which protrudes from the second valve plate, GATE VALVESwhich is located on the inside or outside of the expandable body, and which comes into contact with the valve casing on the side of the first opening of the valve casing.
12. A gate valve according to claim 1, further comprising: a valve casing for enclosing the valve plates in such a manner that the valve plates can freely move; a first valve seat, with which the first sealing member comes into contact, formed in the first opening of the valve casing; and a second stopper which protrudes from the inner wall of the valve casing, which is located on the outside of the expandable body, and which comes into contact with the first valve plate.

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