Study on gas pumping characteristics in radial lip seals

This paper describes a newly developed technique to measure volume of gas moving between the air side and the sump side across a narrow gap between radial lip seals and a rotating shaft. The volume of gas moved was determined with gas chromatograph. Preliminary tests were conducted with standard plane lip seals made of fluoro rubber and nitrile rubber, and with hydrogen and polyalphaolefin as a test gas and a lubricant, respectively. The hydrogen pump rate was almost zero when the shaft was at standstill, and increased with the shaft speed, which suggested that the gas transportation originated from a dynamic effect of fluid flow between the seal and the shaft. The hydrogen pump rate was of the order of 0.1 to 1 cm³/h under the test conditions employed, and appeared to have no strong correlation with the pump rate of the oil. From the consideration of several possible driving forces for the gas flow, it was suggested that the gas was conveyed in the oil that flowed in and out across the sealed gap, though not entirely in the form of dissolved gas in the oil.