Semi-closed type screw compressor

The invention provides a semi-closed type screw compressor which comprises a compressor body, a sliding valve, a sliding valve rod and an oil piston, wherein the compressor body comprises a sliding valve cavity, an oil piston cavity and a partition plate for isolating the sliding valve cavity from the oil piston cavity; a middle passing hole is formed in the partition plate; the semi-closed type screw compressor further comprises a middle supporting sleeve; the middle supporting sleeve is arranged on the middle passing hole in a matched manner and is provided with a sliding valve rod hole; the sliding valve is arranged in the sliding valve cavity; the oil piston is arranged in the oil piston cavity; the sliding valve rod passes through the sliding valve hole, and two ends of the sliding valve rod are respectively connected with the sliding valve and the oil piston. According to the semi-closed type screw compressor, the middle supporting sleeve is arranged on the middle passing hole of the partition plate, so that a support is formed in the middle of the sliding valve rod, and the gravity of the sliding valve can be balanced, so that pressure of the sliding valve to the sliding valve cavity is reduced, abrasion in a moving process of the sliding valve is reduced, the phenomenon of locking is prevented, and the service life of the sliding valve is effectively prolonged.