Seal for oil-free rotary displacement compressor

摘要

Non-contacting cartridge shaft seals prevent leakage loss of process gases in an “oil free” rotary screw compressor or blower, while simultaneously preventing ingress of lubricating oil to the pumping chamber, allowing the compressor/blower to generate process pressure differentials without oil contamination. A compact unitized seal cartridge assembly is provided in the end plates of the pump housing. One of the rotor shafts extends through an aperture in the end plate or housing, between the pumping chamber and oil-lubricated gear/bearing cases. Internal elements have the ability to self-align radially achieving essential concentricity with shaft rotational axes. The rotor shafts or sleeves non-contact relationship during operation allow increased ranges of shaft rotational speeds. Air seal elements restrict flow of process air from the pumping or compression chamber, and oil seal elements with a directional spiral groove on the inside diameter prevent the leakage of lubricating oil to the process or atmosphere.

主权项

1. A seal cartridge for use in a rotary displacement compressor, the compressor having a compressor chamber between two shaft bearings, comprising:
a) a cartridge carrier disposed in a seal cavity annularly around a shaft, the cartridge carrier being shaped, configured and oriented to house at least two self aligning seal rings, each of the two self aligning seal rings including a biasing element to restrain motion of the respective seal ring in the axial direction but permitting limited freedom of motion of the respective seal ring in the radial direction relative to the cartridge carrier, the cartridge carrier further including a fluid communication path in fluid communication with an environment outside the seal cavity, the shaft having a closely controlled outer diameter surface; b) a first oil seal ring being an element of a circumferential shaft seal and being disposed within a cartridge cavity at least partially defined by an inner diameter of said cartridge carrier and sealing between a fluid communication path side and a shaft bearing side, the first oil seal ring being statically sealed against a surface of said cartridge carrier, the first oil seal ring further comprising at least one spiral groove in a machined inner diameter surface thereof, the machined inner diameter surface having very close tolerances, and the at least one spiral groove being shaped, dimensioned, and oriented to provide a dynamic seal between relatively rotating parts by pumping a gas into a gap between the surfaces of the rotating and non-rotating elements of the seal cartridge, the pumping being directed from the fluid communication path side towards the oil bearing side, thereby inhibiting leakage of oil from the bearings along the shaft; and c) a second compressed air seal ring for inhibiting leakage of compressed gas disposed within the cartridge cavity and sealing between the fluid communication path side and a compressor side, the second compressed air seal ring having a machined inner diameter surface with very close tolerances and being statically sealed against a surface of said cartridge carrier, and providing a dynamic seal between the seal cartridge and the relatively rotating shaft; wherein both the machined inner diameter surfaces of the first oil seal ring and the second compressed air seal ring have very close tolerances so as to provide a seal interface with the closely controlled outer diameter surface of the shaft to maintain the gap between at least one of the surfaces in a tight and essentially constant range, thereby causing the radial self alignment of at least one seal ring relative to the seal cartridge throughout a limited range of radial motion while simultaneously maintaining the respective static and dynamic seals, and wherein said closely controlled outer diameter shaft surface and said inner diameter surface of at least one of said first oil seal ring and said second compressed air seal ring are machined so that the very close tolerances interfacing with said closely controlled outer diameter surface of the shaft maintain the gap between said surfaces in a tight and essentially constant range of from about 0.002 to about 0.004 inches, thereby causing the self alignment of each seal ring, so that there is provided a limited range of radial motion of either of the seal rings, resulting from shaft eccentricity, wherein the limited range is from about 0.010 to about 0.125 inches.