Secondary Seal Research Articles

Dynamic Response to Axial Oscillation and Rotating Seat Runout in Contacting Mechanical Face Seals

Contacting mechanical face seals are ubiquitous in many industries, e.g., petrochemical seals, automotive water pump seals, and low pressure gas seals. Environmental awareness and new strict regulations may force an even wider use of contacting seals in limiting leakage of toxic fluids. Contacting operation is achieved when the closing force exceeds a presumed opening force. For prolonged seal life it is desired that the contacting force be as small as possible. On the other hand, the contacting force must be big enough to ensure face contact. To maintain contacting operation the shaft speed must be smaller than some critical value, known as the separation speed. The separation speed is affected by many dynamic parameters of the system, among which is Ike damping of the support. This damping is either inherent in the system, in the form of a secondary seal, or is introduced especially to limit, for example, metal bellows radial vibration. The analysis herein complements an earlier investigation which was limited to undamped seals only. The current analysis reveals that support damping has an adverse effect on the separation speed and wear. Hence, an undamped seal is preferable for a flexibly mounted stator contacting seal configuration.

PETROLEUM GEOLOGY OF THE UNITED ARAB EMIRATES

The Permain to Holocene sediments of the United Arab Emirates consist mainly of epeiric shelf carbonates, associated with minor clastics and evaporites, reflecting major cycles of transgression and regression. These were deposited on the eastern margin of the Arabian Sheild, which lay along the southern margin of the Tethys Ocean during the Mesozoic‐Cenozoic eras. Sedimentation patterns were controlled by prominent regional structural features, epeirogenic movements and/or sea‐level fluctuations.The tectonic history of the UAE in the Mesozoic‐Cenozoic is connected with the opening (Triassic) and closure (Upper Cretaceous‐Paleogene) of the southern Neo‐Tethys Ocean.The distinctive structural style, together with the tripartite development of source‐reservoir‐seal, has produced in the UAE one of the world's richest Jurassic ‐ Cretaceous oil habitats. Significant oil discoveries have also been made in the Permian; Middle and Upper Jurassic; Lower‐Middle‐Upper Cretaceous and Oligo‐Miocene carbonates.Two main source rocks have been identified. One is the Upper Jurassic Diyab/Dukhan Formation, which supplies the most prolific reservoirs in the Upper Jurassic (Arab Formation) and Lower Cretaceous (Thamama Group). The other is the Middle Cretaceous Shilaif/Khatiyah Formation, which feeds both Mishrif and Simsima reservoirs. Other minor potential source rocks have also been identified in the study area.There are two principal sealing formations ‐ the Hith Anhydrite and the Nahr Umr shale; these are the main seals for the oil and gas accumulations in the underlying Arab Formation and Thamama Group, respectively. Secondary seals and barriers also exist in the stratigraphic sequence.

Dynamic Stability Threshold of Contacting Mechanical Seals

The behavior of contacting Mechanical face seals is analyzed. Stiffness and damping coefficients of the secondary seal, face friction, and seal inertia in the presence of eccentric operation and wobbling rotor are fully considered. It is shown that eccentric installation of the seal, relative to the rotor is a major vibration-inducing mechanism and should be minimized. A stability criterion is established for the dynamic angular tilting moments. This provides necessary parameters needed for the design of a stable seal.

Observations On the Curation of Plant and Soil Nematodes

Observations are made on the curation of plant and soil nematodes by reference to the extensive collection of microscope slides and specimens in the Nematology Department, Rothamsted Experimental Station. Better packaging of specimens in transit is required. The addition of 2 % glycerol to fixatives/preservatives to prevent drying out and aid in the processing of specimens to glycerol is recommended. The cuticles of some nematodes degenerate in TAF fixative which should not be used for long term storage. The metal Cobb-type double cover glass slides are more convenient for transport and storage; a longer base cover glass improves clearance for microscope objectives. Cover glass supports need to be much more extensive than in the past to avoid the eventual flattening of specimens. The wax ring seal/support system is quite effective but a secondary seal and cover glass support are recommended. Immersion oil damages some seals and should be removed immediately after use. The drying out of slide mounts is a problem; specimens keep better in glycerol in vials than on slides. Slide mounts should be adequately and clearly labelled in water/oil-proof ink; type slides should be clearly indicated.

Hydrostatic Effects in a Mechanical Face Seal

In a mechanical face seal, the total applied load is supported by hydrostatic and hydrodynamic fluid pressures and often by partial contact of the seal faces. Hydrostatic load support is affected by the initial seal interface geometry and the modification of this geometry due to component distortions. A model developed for static (non-rotating) conditions demonstrates effects of face convergence, spring pressure, and secondary seal friction on the hydrostatic fluid film thickness. The previously reported film thickness probe system has been used to measure the fluid film geometry in a standard wedge-type seal up to 4.5 MPa pressure, for comparison with theory. It is shown that the experimental results verify the hydrostatic model, in particular, confirming the prediction of the hysteresis effect due to the secondary seal friction. Application of the model for a hydrostatic seal design is also discussed. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Tribology Conference i...

Stability Threshold and Steady-State Response of Noncontacting Coned-Face Seals

The dynamic behavior of a noncontacting coned-face seal is analyzed. Stiffness and damping properties of the fluid film and flexible support including elastomeric secondary seal are fully accounted for. Stability threshold and steady-state response in the presence of rotor axial runout and assembly misalignment are investigated. An expression is provided for the critical speed above which the seal becomes dynamically unstable. For stable operation, the relative misalignment between the mating faces is given as a function of rotor runout, assembly misalignment, design parameters, and operation conditions. An expression is provided for the critical rotor runout above which the seal will fail due to face contact. Although the analysis is based on small perturbation assumption, it is shown to be valid in many practical cases.

Design considerations for achieving high vacuum integrity in fusion devices

Achieving high vacuum integrity in fusion devices requires close attention to both the overall system configuration and the design details of joints and seals. This paper describes the factors in selecting the system configuration, from a vacuum standpoint, for the Princeton Plasma Physics Laboratory (PPPL) TFCX-S (toroidal fusion core experiment with all-superconducting toroidal field coils) tokamak device. The TFCX-S driven current tokamak is the eighth design in a series of tokamak concepts defined to cover the magnetic confinement and development gap between the Tokamak Fusion Test Reactor (TFTR) and the Engineering Test Reactor (ETR). The definition of a configuration that minimizes the consequences of leaks is considered a vital activity, as well as the development of leak detection concepts. A major part of the vacuum boundaries of the magnet system and the plasma system is common. For the major penetrations, primary and secondary seals are provided with vacuum control over the region between seals. The intent is to instrument these activities and provide automated recordings of these measurements for leak maintenance.

Operational reliability of end packing of water and chemical pumps

The multiplicity of the designs of end packings of water and chemical pumps is explained by the diversity of their operational conditions and specifications of packings. The following groups of packings having some common constructional features could be identified: packings for chemically neutral media; packings for chemically active media; packings for highly active media; packings for highly abrasive media; and packings for high temperature and low temperature media. Examples are given of some designs of end packings. These packings extensively use siliconized graphites as the friction pair material. The material of the friction pair rings should possess antifriction properties, corrosion resistance, thermal strength and erosion resistance. Rubber rings of circular section are most often used as secondary seals in the design of end packings. Among the main drawbacks of rubber seals is their tendency to aging. Bellows made of rubber, Teflon and metal represent more perfect secondary seals. Springs used in sealing systems absorb all of the vibrations of the packings, they experience variable stresses and undergo fatigue failure. The paper describes the failure modes of each component of end seals in more detail and suggests methods for alleviating the problems associated with each one.

Dynamic Analysis of Noncontacting Face Seals

The dynamic behavior of a noncontacting coned face seal is analyzed for the case of a rigidly mounted rotating seat and a flexibly mounted stationary ring taking into account various design parameters and operating conditions. The primary seal ring motion is expressed by a set of nonlinear equations for three degrees of freedom. These equations, which are solved numerically, allow identification of two dimensionless groups of parameters that affect the seal dynamic behavior. Stability maps for various seals are presented. These maps contain a stable-to-unstable transition region in which the ring wobbles at half the shaft frequency. The effect of various parameters on seal stability is discussed and an approximate expression for critical stability is offered. The theoretical model assumes frictionless flexible mounting of the seal ring such as in metal bellows. However, the results for critical stability can also be used as an upper limit for cases when friction in the secondary seal is present.

Dynamic Response to Rotating-Seat Runout in Noncontacting Face Seals

The dynamic response of a flexibly-mounted ring to runout of the rotating seat in mechanical face seal is analyzed assuming small perturbations. It is found that tracking ability of the stator depends only on its dynamic characteristics and operating conditions and is not affected by the amount of runout. Three different modes of dynamic response are shown and the condition for parallel tracking is presented. The present analysis is limited to flat-faced seals with no secondary seal damping. Nevertheless it provides a good insight into the dynamic behavior of noncontacting face seals.

Radial Forces in a Misaligned Radial Face Seal

Radial forces on the primary seal ring of a flat misaligned seal are analyzed, taking into account the radial variation in seal clearance. An analytical solution for both hydrostatic and hydrodynamic effects is presented that covers the whole range from zero to full angular misalignment. The net radial force on the primary seal ring is always directed so as to produce a radial eccentricity which generates inward pumping. Although the radial force is usually very small, in some cases it may be one of the reasons for excessive leakage through both the primary and secondary seals of a radial face seal.

Steady-State and Dynamic Analysis of a Jet Engine, Gas Lubricated Shaft Seal

Dynamic response of a gas-lubricated, jet-engine main shaft seal was analytically established as a function of collar misalignment and secondary seal friction. Response was obtained by a forward integration-in-time (time-transient) scheme, which traces a time history of seal motions in all its degrees of freedom. Results were summarized in the form of a seal tracking map which indicated regions of acceptable collar misalignments and secondary seal friction. Methodology, results and interpretations are comprehensively described.

High Noise Reduction Ear Enclosures

Personnel associated with operation and maintenance of combat vehicles and military aircraft are subject to noise environments so severe that the available ear protective devices do not provide adequate noise reduction. A study and development program has been conducted to improve available noise reduction by (1) design of an ear enclosure cushion to provide a better seal at low frequencies; (2) provision of a secondary seal inside the earcup between the communications earphone and the ear canal, and (3) utilization of electronic noise cancellation to improve further the noise reduction at low frequencies. The design evolved from this study features a low-profile ear enclosure in which the earcup and cushion form a smooth continuous shell that is curved inward to rest behind the pinna. The cushion is fabricated from material which has frequency-dependent viscoelastic properties. It is compliant at low frequencies to provide a good seal, but stiff at autio frequencies to act as an extension of the earcup wall. The design requirements that have been met provide for better than 20 dB noise reduction at low frequencies and better than 45 dB at high frequencies. [Supported by the U. S. Army, under contract.]

Secondary seals of graphite for mechanical seals : W. V. Adams, Lubrication Eng., 27 (2) (1971) 54–57; 3 figs., 1 table

Secondary seals of graphite for mechanical seals : W. V. Adams, Lubrication Eng., 27 (2) (1971) 54–57; 3 figs., 1 table

Selection, Analysis and Preliminary Design of a Steam-Lubricated, Steam-Turbine, Shaft Seal

Steam turbine efficiency can be improved by large diameter, high speed stages, provided seal leakage and friction, and wheel windage losses can be contained. This paper describes analysis and design of a steam-lubricated seal applied to a single stage experimental turbine designed for improved efficiencies over conventional types. Proper performance of the seal is vital to overall turbine performance. The seal is subjected to surface speeds of approximately 75,000 fpm and up to 100 psi pressure differential. A sectored fluid film seal that uses hydrostatic steam secondary seals was found to be the best candidate configuration. The sectored seal is considered optimum for tracking capability, although there are limitations on the amount of collar nutation permitted. A description of the computerized steady-state and dynamic analyses are described in an appendix. Presented at the 25th ASLE Annual Meeting in Chicago, May 4–8, 1970

Configurations for gas-turbine compressor end seals : J. W. Bjerklic, L. Ludwig and D. F. Wilcock, Lubrication Eng., 25 (4) (1969) 169–175; 16 figs., 1 table, 1 ref.

Gas turbine compressor end seals, discussing air leakage paths, primary and secondary seals, design and efficiency