Water injection type screw fluid machine

1. A water injection type screw fluid machine, in which a target gas is compressed or expansion force of the target gas is converted into turning force by intermeshing male and female screw rotors housed in a rotor chamber formed in a casing, while water is injected inside the rotor chamber to lubricate the screw rotors, the screw fluid machine comprising:

a first non-contact seal, a second non-contact seal, and a lip seal, which are disposed between the rotor chamber and a bearing for a rotor shaft of the screw rotor and in this order from the rotor chamber side;

a pressurized communicating channel for introducing the target gas which is at high pressure into a pressurized space formed between said first non-contact seal and said second non-contact seal; and

an open communicating channel, through which an open space, which is formed between said second non-contact seal and said lip seal, opens to an outside of the casing.

2. The water injection type screw fluid machine according to claim 1 , wherein:

the bearing is a bearing on the high pressure side, and

the water injection type screw fluid machine further comprises a low pressure communicating channel for allowing an outflow space, which is formed on the rotor chamber side with respect to said first non-contact seal, to be communicated with a low pressure space inside the rotor chamber or a low pressure channel for the target gas, which is in communication with the rotor chamber.

3. The water injection type screw fluid machine according to claim 1 , wherein:

the water injection type screw fluid machine is a water injection type screw compressor for compressing the target gas;

further comprises a water recovery unit for separating the water from the target gas that is discharged; and

supplies the target gas, from which the water is separated in said water recovery unit, through a pressure reducing means to said pressurized communicating channel.

4. The water injection type screw fluid machine according to claim 3 , supplies the target gas, from which the water is separated in said water recovery unit, through a dryer to said pressurized communicating channel.

5. The water injection type screw fluid machine according to claim 4 , wherein an on-off valve, which is closed when operation of the water injection type screw fluid machine is stopped, is installed in said pressurized communicating channel or in a flow path between said water recovery unit and said pressurized communicating channel.

6. The water injection type screw fluid machine according to claim 1 , further comprising a sleeve member fittingly mounted around the rotor shaft, said sleeve member located in said open space and equipped with a flange projected toward a radial outside.

7. The water injection type screw fluid machine according to claim 1 , wherein each of said first and second non-contact seals includes: a fit member having opposed surfaces formed so as to be opposed to each other across an interval along an axial direction; two seal rings, which are respectively contacted with the opposed surfaces; and an elastic member disposed between said two seal rings to push said seal rings against the opposed surfaces.