Compressor with liquid injection cooling

A compressor comprising:

• a casing with an inner wall defining a compression chamber, an inlet leading into the compression chamber, and an outlet leading out of the compression chamber;
• a rotor rotatably coupled to the casing for rotation relative to the casing such that when the rotor is rotated, the compressor compresses working fluid that enters the compression chamber from the inlet, and forces compressed working fluid out of the compression chamber through the outlet;
• a gate coupled to the casing for reciprocating movement relative to the casing, the gate comprising a sealing edge, the gate being operable to move relative to the casing to locate the sealing edge proximate to the rotor as the rotor rotates such that the gate separates an inlet volume and a compression volume in the compression chamber;
• and
• a mechanical seal located at an interface between the gate and casing, the mechanical seal comprising:
• first, second, and third seals disposed sequentially along a leakage path between the gate and casing,
• a source of pressurized hydraulic fluid, and
• a hydraulic fluid passageway that connects the source to a space along the leakage path between the second and third seals so as to keep the space pressurized with hydraulic fluid.