Patent ID: 7614862

Claim:
Water-injected screw compressor element comprising: a housing confining a rotor chamber with an inlet on an inlet side and an outlet on an opposed outlet side and in which first and second co-operating rotors are provided which are mounted in the housing on respective first and second rotor shafts by water-lubricated bearings at first and second ends of each of the first and second rotor shafts; a water circuit for the injection of water under pressure which opens into the rotor chamber and at the location of said water-lubricated bearings; at the inlet side of the rotor chamber the first rotor is provided with a first piston and a second piston which can be respectively axially shifted in a first guide and a second guide, and the second rotor is provided with a third piston and a fourth piston which can be respectively axially shifted in a third guide and a fourth guide; the first piston positioned on the first rotor shaft between a first pressure chamber and a second pressure chamber, the second piston positioned on the first rotor shaft between the second pressure chamber and the first rotor, the third piston positioned on the second rotor shaft between a third pressure chamber and a fourth pressure chamber, the fourth piston positioned on the second rotor shaft between the fourth pressure chamber and the second rotor; the first and second pressure chambers connected via a first leakage connection, the third and fourth pressure chambers connected via a second leakage connection; and wherein, the first pressure chamber is connected, via a first branch, to the rotor chamber for feeding the first pressure chamber with water that is branched off from the rotor chamber, the second pressure chamber is connected, via a first pipe, to the rotor chamber and fed with water flowing from the first pressure chamber via the first leakage connection, the third pressure chamber is connected, via a second branch, to the rotor chamber for feeding the third pressure chamber with water that is branched off from the rotor chamber, the fourth pressure chamber is connected, via a second pipe, to the rotor chamber and fed with water flowing from the third pressure chamber via the second leakage connection; wherein the first and third pressure chambers are connected, via the first and second branches, to the rotor chamber and the second and fourth pressure chambers are connected, via the first and second pipes, to the rotor chamber; and wherein axial force components exerted by compressed gasses on the first and second rotors are offset at least in part by pressures within the first, second, third, and fourth pressure chambers acting on the respective first, second, third, and fourth pistons.