Principle of operation and computational method for floating ring seals

Abstract

Groove seals of centrifugal machines rotors are the simplest and most reliable type of seals. In addition to the function of sealing, they perform an equally important function, which is to improve the vibration state of the rotor. These functions contradict each other, since an increase in hydraulic resistance worsens the dynamic qualities of the seals, their hydrostatic stiffness and damping. An alternative to conventional groove seals are floating ring seals that provide the required reliability and tightness. The principle of operation and method of computation seals with floating rings are considered. The behavior of the floating rings is determined by the ratio of forces in the ring and end chokes. Floating ring seals are a combination of mechanical and groove seals operating in lighter conditions: the ability of the floating ring to be centered relative to the rotating shaft due to the hydrodynamic forces in the annular gap allows to reduce radial clearances and thereby significantly reduce leaks. A self-centering floating ring can be considered as an oscillatory system with four degrees of freedom, performing forced oscillations under the action of kinematic excitation from the shaft. Possible variants of floating rings operating conditions are analyzed. It is shown that conditionally movable rings are more effective and reliable, since they have increased static and dynamic stability, providing the required tightness and increased service life of the seals. Expressions are obtained that determine the conditions for the radial and angular immobility of the rings. It is concluded that floating ring seals are in many cases more effective when the rings are not floatable.