A valve includes a valve body, a valve plate, and an actuation mechanism, wherein the valve body includes two plates parallel to each other and symmetrical and on which medium access holes are correspondingly opened; sealing rings a are symmetrically provided on inner surfaces of the two plates, and the medium access holes on the two plates are completely located within circumferentially closed holes of the sealing rings a; the valve plate has a smooth surface and is tightly sandwiched between the sealing rings a when the valve is closed; a fastening structure is installed on the two plates of the valve body and clamps the two plates and/or the sealing rings a around radial peripheries of the sealing rings a; and at least a part of the fastening structure can adjust its clamping degree in a direction perpendicular to a surface of the valve body.