Investigation of seals with floating rings in a screw compressor

Abstract

A number of screw compressors (SC) produced in the Soviet Union for air compression to a pressure of 1.5-2.5 kg/cm 2 use metallic labyrinth seals. The efficiency of these seals decreases rapidly as discharge pressure increases. Replacing these labyrinth seals by better designs can substantially reduce air leakage through the end seals of the SC and can improve their efficiency. This articles presents some results of full-scale investigations of seals with prestressed floating graphite rings used on an experimental screw compressor (ESC). The advantage of these seals is their simple construction and ability to operate at high peripheral speeds and small radial gaps [1, 2]. The seal investigated (Fig. 1) had four sealing rings. It was installed in the ESC on the discharge side replacing a static labyrinth seal. The seal could be used with or without seal liquid due to the design of the seal and the body of the ESC. The design of the body of the ESC also allowed the seal investigation to be carried out without intermediate collection of leakage from the seal chamber. The openings connecting the seal chambers were plugged to eliminate the interactive influence of the seals on their operation. During assembly of the seal the radial gap h r between the sealing rings and the bushings installed on the compressor rotors was 0.03-0.04 mm and the axial gap h e between the sealing and intermediate rings was 0,10-0.12 ram. The seal bushing was fabricated of 2Kh13 steel and the seal rings of 2F-1000 carbon-graphite. A metal band (1KhlSN10T steel) was pressed onto the outer surface of the hot graphite sealing rings. The metal band was heated up to 550~ for 15 min in a muffle furnace before pressing onto the graphite rings. The pressing operation was carried out at ambient (20~ air temperature and did not last more 10-15 sec. The prestressed rings were slowly cooled to ambient air temperature after the pressing and were then finished by machining [3]. 2