Radial Seals Research Articles

Effect of reduction in seal clearances on leakages in a rotary heat exchanger

An experimental investigation was undertaken of the effect of seal clearances on leakages in a rotary regenerator. The measurements were carried out before and after a reduction in radial seal clearances. On the basis of these measurements the direct effect of reduction in seal clearances on leakages was shown.

An Experimental Investigation of Oil-Buffered Shaft Seal Flow Rates

An experimental investigation was conducted to identify an optimum oil-buffered shaft seal for use on centrifugal compressors, with the primary objective being minimal seal oil exposure to process gases that cause seal oil degradation or are toxic. Types of seals tested included smooth bore cylindrical bushings, spiral groove cylindrical bushings, radial outward-flow face seals, and radial inward-flow face seals. The influence of shaft speed, gas pressure, seal oil differential pressure, oil bypass flow rate, and oil supply temperature on process side seal oil flow rate was determined. The investigation revealed some surprising relationships between seal oil flow rates and the escape of process gas.

An Experimental Study of Hydrodynamic Film Rupture in a Steadily-Loaded, Non-Conformal Contact

A study of ventilated gaseous cavitation in a steadily-loaded, non-conformal contact has been undertaken. The work is particularly appropriate to what can be called ‘lightly loaded’ situations such as those occurring in radial race seals and certain industrial coating processes. A wide-ranging experimental programme has been carried out and measurements of film rupture location and pressure distributions compared to computer predictions obtained using the cavitation boundary conditions of Coyne and Elrod. Photographic studies are also reported. The boundary conditions due to Coyne and Elrod have been confirmed as appropriate for the experimental conditions studied.

Seizure of Eccentrically Loaded Journal Bearings and Sealing Rings

Thermal and elastic deformations are derived for a ring receiving heat input over a limited part of its inner circumference. This is applied to the problem of seizure of journal bearings or radial seals operating with dry or boundary lubricated contact. It is found that when the ratio of outer to inner radius for the ring is less than 1.715, seizure will not occur as a result of the mode of distortion studied. For thicker bearing/housing bodies there is always some load-speed combination which will lead to seizure, and this may occur in the range of common speeds and loads encountered in engineering applications.

Lip Motion—An Important Factor in Seal Design and Performance

A method of measuring circumferential and radial seal lip motion by means of a stereo phonographic cartridge is described. Also, five seal variables, viz., flex section thickness, lip length, seal unsprung diameter, lip material, lip force and two shaft variables, shaft out-of-round (OOR) and number of lobes, were investigated by means of a fractional factorial experiment to determine the effects of these seven variables on circumferential and radial lip motion. The two shaft variables, shaft OOR and number of lobes had significant effects on circumferential lip motion at the five percent significance level. Shaft OOR, seal lip material, number of lobes, and five interactions, flex section thickness/shaft OOR, lip length/shaft OOR, lip length/number of lobes, shaft OOR/number of lobes, and number of lobes/seal lip material, showed a significant effect on radial lip motion at the one percent level. Two interactions, lip length/seal lip material and shaft OOR/lip force, were significant at the five percent level.

Heat distribution and flash temperatures in radial seals

A method is described for the calculation of the flash temperatures in radial fluid seals during dry friction of the rotating shaft on the stationary seal. For a particular case of practical interest, diagrams are given for the hand computation of the flash temperatures. It was found that previous models can introduce considerable error in this calculation.

Analysis of the Shrouded Rayleigh Step Pad for an Incompressible Fluid Film with the Centrifugal Inertia Effect Included

A computer program was developed to calculate the load capacity of the hydrodynamic forces generated within an incompressible fluid film by a shrouded Rayleigh step pad for application in a radial seal design. The program makes use of the central-difference operator, defined for cylindrical coordinates, to approximate the pressure gradient over the pad. Solution of the lubrication equation with the centrifugal inertia effect included is achieved by employing a noniterative numerical routine. Pressure maps and flow fields based on the geometry for a Rayleigh pad were obtained. Results indicate that the selection of a pad geometry such that the design load intersects the dimensionless load capacity curve at a separation ratio between two and four will yield the most favorable operating characteristics, i.e., the best trade-off between high load capacity, high film stiffness, high tangential flow, and a minimum temperature rise.

Normal Stresses at High Shear Rates in a Polymer Solution

Based on an examination of the characteristics of shear viscosity versus shear rate, it was postulated that high tensile and compressive stresses might exist in certain liquids at very high shear rates. If obtainable, these stresses could be important as load-bearing mechanisms in high-speed machine elements, and as a sealing mechanism in radial face seals. Such stresses should be evident in a polymer fortified oil, or in a liquid comprised of molecules possessing an appreciable length to width ratio. Therefore, a jet reaction viscometer reaching 107 sec−1 shear rate was developed to explore this possibility. Tests with polyisobutylene dissolved in a kerosene showed that elastic stresses were dominant with respect to viscous stresses at high shear rates. Tensile stresses up to more thn 1000 psi were obtained. However, the life of the polyisobutylene molecule was short. Hence it is concluded that normal stresses of appreciable magnitude can exist in high-speed machine elements under favorable conditions to affect their operation.

Zero Leakage: Results of an Advanced Lip Seal Technology

The advent of the “Helixseal,” a type of hydrodynamic sealing element, to the automotive industry has provided a means for greatly reducing sealing problems with very little increase in production cost. A new sealing technology, developed during a 10-year program at the General Motors Research Laboratories, has involved detailed studies to optimize the basic sealing parameters of radial lip-type seals. Although all elements of a conventional lip seal design can be optimized, the frequency of seal failure is still intolerable due to the large number of production variables which affect leakage. Consequently, it was necessary to explore and develop a means of complementing the lip seal, whereby increased reliability could be assured. The Helixseal is based upon hydrodynamic principles which allow the generation of controlled fluid forces. It consists of angular pumping vanes, applied to the seal face to provide a viscous shear force that opposes leakage of the fluid film. Optimized design of the Helixseal can assure zero leakage in seal applications.

Fundamental Research on a Radial Face Seal

Radial face seals generally speaking operate under full hydrodynamic lubricating conditions, but the mechanism of lubrication is not completely understood. In a primarily experimental investigation the author has attempted to establish a description of the basic lubricating mechanism in radial face seals. The experimental apparatus and measuring techniques are briefly described. The experimental results display a high degree of reproducibility. Dynamic measurements of film thickness reveal fluctuations at twice shaft speed frequency that are concluded to be due to surface waviness. This conclusion is corroborated by the topography of the sealing faces. At constant geometry the friction coefficient and film thickness appear to depend on two dimensionless numbers incorporating average face pressure, sealing pressure, viscosity and speed. A simplified theory that lakes into account the macroroughness of the sealing faces shows close correlation with the experimental data obtained. Having obtained a strong in...