Patent ID: 7726659

Claim:
A static pressure type non-contact gas seal including: a tubular seal case; a rotary sealing ring fixed to a rotary member; a stationary sealing ring held to be axially movable in the seal case with facing the rotary sealing ring; an opening force generating means for generating an opening force that acts on the stationary sealing ring in a direction to open the space between the facing end surfaces, serving as the sealing end surfaces, of both the sealing rings, by supplying seal gas to the space between the sealing end surfaces from a joined seal gas passage passing through the seal case and the stationary sealing ring; and a closing force generating means for generating a closing force that acts on the stationary sealing ring in a direction to close the space between the sealing end surfaces, thereby so as to keep the sealing end surfaces in a non-contact state by a balance of the opening force and the closing force; and wherein the closing force generating means, which does not use a spring, is so configured that an annular-spaced back pressure chamber is formed by blocking with two O-rings between the facing peripheral surfaces of the seal case and the stationary sealing ring to introduce thereinto a portion of the seal gas to be supplied to the seal gas passage or a portion of the seal gas flowing through the seal gas passage, so as to generate the closing force as a back pressure caused by the seal gas that acts on the stationary sealing ring; and a pressure keeping chamber is formed between the facing peripheral surfaces of the seal case and the stationary sealing ring, to generate a resistance force for preventing the stationary sealing ring from moving toward the rotary sealing ring by the seal gas introduced thereinto, and a seal gas introducing passage is formed in the stationary sealing ring, to make the pressure keeping chamber communicate with the back pressure chamber or the communication space and has a throttle disposed therein, so that the stationary sealing ring is prevented from moving rapidly toward the rotary sealing ring when supply of the seal gas stops; and wherein the seal gas passage includes an annular-spaced communication space which is formed between the facing peripheral surfaces of the seal case and the stationary sealing ring by blocking with the two O-rings mounted between the facing peripheral surfaces, a case-side passage that passes through the seal case provided with an upstream end connected to the seal gas supply passage and a downstream end opened to the communication space, a static pressure generating groove that is formed in the sealing end surface of the stationary sealing ring, a sealing ring-side passage that passes through the stationary sealing ring provided with an upstream end opened to the communication space and a downstream end opened to the static pressure generating groove, and a throttle that is disposed in the sealing ring-side passage; and the back pressure chamber is also used as the communication space of the seal gas passage.