Principles of Gas-Lubricated Shaft Seals

Four types of gas-lubricated seals for rotating shafts are described, each based on a corresponding type of gas bearing. These seals are the hydrodynamic disc seal (based on the spiral-groove thrust plate), the hydrostatic disc seal (based on a hydrostatic full-face thrust plate), the hydrodynamic sleeve seal (based on a hydrodynamic full journal bearing), and the hydrostatic sleeve seal (based on a hydrostatic journal bearing).

Each seal consists of two parts, a gas-bearing region and a gland region. The gas-bearing region must provide a gas film of the correct thickness between the seal surface, and this film must be sufficiently stiff to prevent excessive vibration. The gland region, which is the seal proper, must restrict the flow of gas into and out of the sealed system to a minimum acceptable standard. The theory of the gas-bearing region of the seals is based on standard gas-bearing principles and these have been summarized into a form suitable for seal application. The theory of the gland region is that of gas flow between parallel surfaces and this is described only in the viscous flow regime.

To clarify the principles of the seals, examples are given of the design of each type of seal for use on a 2-in. diameter shaft operating at 9000 rev/min with zero pressure in the sealed system.