Mechanical Seal Design Research Articles

Hydrostatic effect of rectangle micro-texture on liquid-lubricated mechanical seal

In this paper, the hydrostatic effect of rectangle micro-texture (RMT) on liquid-lubricated mechanical seal is numerically investigated. A model of liquid-lubricated mechanical seal with RMT is developed with finite element method (FEM). The hydrostatic effect of the RMT and the circular micro-texture (CMT) on the partial surface micro-texture liquid-lubricated mechanical seal are compared and analysed. Results show that the optimised RMT can greatly improve the hydrostatic opening force of liquid-lubricated mechanical seal. The hydrostatic opening force of the RMT with the orientation factor g = 1/3 is about 18% larger than that of the CMT in the typical case. Furthermore, the influence of the RMT orientation factor on the hydrostatic opening force, the leakage and the efficiency parameter of mechanical seal design are discussed under different operating parameters and micro-texture parameters.

Calculation Method of Mechanical Face Seal Temperature Based on Heat Conduction Angle

It is a key technology in the design and application of mechanical seals as how to determine and control its face temperature. According to the explicitly defined heat conduction angle, supposed the surfaces of the stator ring are insulation, and the heat produced by friction of seal faces transfers only through the rotor ring along the heat conduction angle, an approximate analytical method calculating the end face temperature distribution of mechanical seal was developed for mixed friction condition in this paper. The heat conduction angle, angular velocity, contact pressure and other factors and its law on end face temperature distribution have also been analyzed in this paper. The results of this method for calculating the end face temperature are much closer to the reality, compared with other approximate analytical methods.

Optimum Design of Flat End Face Mechanical Seal Based on Coupling Analysis

The flat end face mechanical seals are widely used in shaft sealing at moderate rotational speed. The thermal deformation of the rotating and stationary rings initiated by friction heat of fluid film should be primarily considered in the design of mechanical seal. In consideration of the coupling effect among the thermal deformation of sealing rings, the fluid flow in the gap composed by end faces of sealing rings and the heat transfer from fluid film to sealing rings, the optimum design method for flat end face mechanical seal is established. The end faces are fabricated to form a divergent gap at the inner side of the sealing rings, and a convergent gap will occur at the outer side and a parallel gap will be obtained at where the original divergent gap is due to the thermal deformation. After optimization, the leakage rate can be reduced while the bearing force of fluid film is still large enough to keep the fluid lubrication of the end faces.

The performance of mechanical seals used in a high vibration environment

Cooling pumps found in high-power diesel engines experience high levels of vibration. Combined with long operating periods this can lead to the failure of mechanical seals used in these pumps. This feature article discusses a test facility, which was set up to investigate the problem, and the test results obtained from a wide range of mechanical seal designs. The performance-to-price ratio of the seals was then established to help users choose the best and most economical seal for their specific application.

Frictional heat transfer regularity of the fluid film in mechanical seals

The frictional heat transfer regularity in the mechanical seal system consisting of the rotating ring, the stationary ring, the fluid film in the end faces and the sealed medium was investigated. The primary factors affecting the frictional heat transfer regularity, such as the heat transfer coefficients from the rings to the sealed medium, the frictional heat flux, the frictional heat distribution ratio and so on, were discussed. The equations for calculating the temperature field both in the sealing members and in the fluid film were derived. The coupling analysis of the frictional heat of the fluid film and the thermal deformation of the two end faces of the rings was carried out to obtain the separation angle of the two deformed end faces in consideration of the viscosity change of the fluid film. The results indicate that the frictional heat of the fluid film heavily affects its characteristic and the sealing performance of mechanical seals. The frictional heat changes not only the shape of the gap between the end faces but also the viscosity of the fluid film, and thereupon leads to the increase of the leakage rate. The maximum temperature of the system is at the inner radius of the fluid film, and most of the frictional heat is conducted by the rotating ring. Based on the heat transfer analysis method put forward in this paper, the parameterized design of mechanical seals can be realized to determine the best geometrical parameters and to select the appropriate material of the sealing members.

New mechanical seal designs and catalogue introduced

New mechanical seal designs and catalogue introduced

Improving the reliability of mechanical seals in ethylene oxide applications

Mechanical seals in ethylene oxide service can sometimes fail within a very short time, often with severe damage to perfluoroelastomer secondary seals that would normally be expected to give long service. This feature provides an insight into the problems and solutions for mechanical seal design, material specification, and system commissioning to ensure robust and effective sealing of this potentially hazardous media.

An Improved Design of Spiral Groove Mechanical Seal

Abstract The coupling effect among the flow of fluid film, the fractional heat of fluid film and the thermal deformation of sealing rings is inherent in mechanical seals. The frictional heat transfer analysis was carried out to optimize the geometrical parameters of the sealing rings, such as the length, the inner radius and the outer radius. The geometrical parameters of spiral grooves, such as the spiral angle, the end radius, the groove depth, the ratio of the groove width to the weir width and the number of the grooves, were optimized by regarding the maximum bearing force of fluid film as the optimization objective with the coupling effect considered. The depth of spiral groove was designed to gradually increase from the end radius of spiral groove to the outer radius of end face in order to decrease the weakening effect of thermal deformation on the hydrodynamic effect of spiral grooves. The end faces of sealing rings were machined to form a divergent gap at inner radius, and a parallel gap will form to reduce the leakage rate when the thermal deformation takes place. The improved spiral groove mechanical seal possesses good heat transfer performance and sealing ability.

Design of mechanical seals for hygienic and aseptic applications

This article is an extended summary of the report prepared by the Mechanical Seals Subgroup of the European Hygienic Equipment Design Group (EHEDG). Originally published in August 2002, it is the 25th in the series of EHEDG summaries published in TIFS. The full report was prepared by G. Anderberg (Chairman), R. Cocker, R. Curiel, R. Feenstra, W. Mathes, H van Eijk and R. Wallis and is available from CCFRA at pubs@campden.co.uk. Information about EHEDG can be found on the website at www.ehedg.org. The production of EHEDG guidelines is supported by the European Commission under the Quality of Life Programme, project HYFOMA (QLK1-CT-2000-01359). For application in the field, it is strongly recommended that the guideline be read in its entirety.

Advisory board member honoured by ASME

Dr Richard Salant, a professor at Georgia Institute of Technology, Atlanta, has been honoured by the American Society of Mechanical Engineers (ASME). He was recognized for pioneering contributions to mechanical seal and lip seal design through his research into the mechanisms of seal operation and development of predictive mathematical performance models. This is a short news story only. Visit www.worldpumps.com for the latest pump industry news.

On the tribological behaviour of mechanical seal face materials in dry line contact: Part II. Bulk ceramics, diamond and diamond-like carbon films

The evolving tribological demands of mechanical face sealing applications such as those associated with high-duty fluid seals and gas sealing technology are driving the need for the development of new and novel seal face material solutions. Under conditions where the combination of high pressure and high surface speeds create high levels of PV the seal designer will specify two hard faces, typically a combination of reaction bonded silicon carbide, alpha sintered silicon carbide or tungsten carbide. Work has been carried out here aimed at evaluating and increasing the understanding of the tribological nature of these hard face combinations and evaluating the potential of polycrystalline diamond (PCD) and diamond-like carbon (DLC) films. Experimentation has shown that under dry moderate contact conditions mild deformation-controlled wear takes place with a polishing of the contact surfaces. Progressively increasing the contact pressure was shown to eventually produce a transition to severe microcrack-controlled wear. Coating one of the contact surfaces with a PCD or DLC film modified the contact dynamics producing low friction coefficients and in the case of the PCD film shifted the wear transition to a much higher contact severity. A linear elastic contact model is developed that provides a framework for rationalising the results of this work and enables the key features of mechanical face seal design to be related to the critical tribological characteristics of the seal face material systems.

2D numerical modelling of the TEHD transient behaviour of mechanical face seals

This feature describes how a thermohydrodynamic (THD) transient model of an aligned face seal during start-up has been improved by including a thermoelastic distortion calculation, using the method of influence coefficients. It compares the results obtained with this 2D transient model, when the steady state is reached, with those of a 3D stationary model, which were experimentally validated. A case of thermal instability illustrates how the thermoelastohydrodynamic (TEHD) model may be useful in optimizing mechanical seal design.

A Non-Axisymmetric Steady State Model of a Mechanical Seal for Down-Hole Tools

A non-axisymmetric steady state numerical model has been developed for use in the design of mechanical seals for down-hole tools. It is applicable to other types of mechanical seals in which friction from the static secondary seal is significant, as well. This model predicts such quantities as leakage rate, external fluid incursion rate, film thickness distribution, fluid pressure and contact pressure distributions, interface temperature and face deformation. Model results show that for a given set of operating conditions, there is a range of equilibrium states of the seal, corresponding to a range of inclinations of the non-rotating seal face relative to the rotating face. Depending on the inclination, it is possible to have negative leakage due to the asymmetry of the film thickness distribution. Even with positive leakage, under some circumstances incursion of the external fluid can occur as a result of the asymmetry.

Computer prediction of mechanical seal performance and experimental validation

Correct prediction of the mechanical seal performance is essential to reduce the time and cost of new product development. For many years the knowledge gained from tribology research has laid a sound foundation for seal performance prediction. As a result of long-term commitment by John Crane EMA, a personal computer based software CSTEDYSM has been developed and continuously refined and validated since 1992. The recent development of the computer model through experimental investigation and extensive experimental validation has confirmed the accuracy and reliability of the model. This gives confidence in application of the software to mechanical seal design and performance optimization, special product application and trouble shooting. It is estimated that a new product development period can be cut significantly due to the implementation of this software.

Design and selection of mechanical seals to minimize emissions

The design of mechanical seals for applications requiring the control of fugitive emissions is reviewed. The paper discusses the features inherent in seal design and how these affect overall performance; it also examines the effect of materials of construction. Selection guidelines comparing various mechanical seal arrangements are included, these being based on operational experience in working plants. Significant events in the development of emission regulations and therefore modern sealing solutions are described.

Improvement of Performance of Mechanical Seals under High-Temperature and High-Pressure Conditions. 2nd Report. Structural Improvement and Design of Mechanical Seals.

The aim of the present study is to present improvements of mechanical seal performance for use under high-temperature and high-pressure conditions. Existing mechanical seals subjected to both high and low pressure show unstable leak rate and sliding reliability. Under high-temperature conditions, the temperature of seal face increases and thermal deformation of seal face takes place, leading to a decline in seal performance. We consider a new structure of the mechanical seal that cools the seal ring and seal face quickly, as well as the roughness and balance ratio of the seal to design. We derive the shape of the mechanical seal from experimental data. We also confirm that this seal exhibits the stable leak rate and sliding reliability under these conditions.

Effect of Fluid Inertia Force on Performance of Noncontact Mechanical Seals.

The aim of the present study is to represent a probability to design of step shape noncontact mechanical seals under high-speed and high-pressure conditions for water pumps. Existing contact-type mechanical seals under these conditions show unstable seal performances. For a noncontact mechanical seal, we estimate the leak rate and obtain the conditions for stability and reliability. We derive equations for calculation of the leak rate, taking into consideration the influence of fluid inertia force by defining S, an inertia coefficient. Since the leak rate is influenced by fluid inertia force, it decreases as speed increases. We found that seal face stiffness is important in calculating seal dimensions and developed a diagram for seal design which takes into account fluid inertia force.

Critical Balance Ratio of Mechanical Seals

In this paper, several failure modes related to mechanical seal balance ratio are introduced, such as seal face opening, premature wear, dry running, heat checking, blistering, phase stale instability, seal face tilling instability, fluid film instability, inhibition of fluid film formation, fluid film rupture, vaporization and excessive liquid leakage. Formulae for critical balance ratios for these failure modes are presented. Suitable balance ratios can be selected by considering these critical balance ratios. Several examples are given for mechanical seal design and application.

Innovations For Rotating Equipmentactive Magnetic Bearings And Mechanical Dry Seal Systems

Abstract In an effort to improve the reliability of high pressure centrifugal compression equipment, NOVA Corporation of Alberta began a program in the early 1970s to find alternatives to lube and seal oil systems. This program was successful, resulting in the application, testing and utilization of mechanical dry gas seals and active magnetic bearings in NOVA 's gas transmission system. This paper covers the development history of dry seals and magnetic bearings for centrifugal compressors in high pressure natural gas service. The operating principles, experiences and advantages of mechanical dry seals and active magnetic bearings are also discussed. History NOVA Corporation of Alberta has over 30 years of experience with pipeline and compressor equipment associated with the planning, design, construction, operation and maintenance of a 14 000 km natural gas transportation system. This system includes 36 compressor stations totalling 388 mW, 825 major receipt and delivery stations and carries over 75% of marketed Canadian natural gas production. Centrifugal compressors inherently present operating problems associated with maintenance, reliability, and safety. As an operator of 63 gas turbine compressor units, NOVA has always been concerned with these operating problems. Internal studies conducted in the early 1970s indicated that over 80% of the downtime on NOVA's centrifugal compressors was related to problems with the seal or lube oil systems. This prompted NOVA to initiate a program aimed at the elimination of these oil systems. In 1976, NOVA entered into a joint development program for a mechanical dry 1$ seal with John Crane Inc. By 1978, a dry seal was available witch reliably replaced the conventional seal oil system in centrifugal compressors. Dry seal development and enhancement continues. NOVA is also working with Pacific Wietz, a German seal manufacturer, on the application of an alternative design of a mechanical dry seal. In 1982, NOVA became aware of a new device developed by a French manufacturer (Societe de Mecanique Magnetique -S2M) which could be the key to completely eliminating the oil system in centrifugal compressors. This device was an active magnetic bearing system. A prototype was installed in one of NOVA's operating compressors which had already been retrofitted with mechanical dry seals. NOVA was pleased with the results on the prototype installation, and has been engaged in a product enhancement and retrofit program since that time. In 1984, Magnetic Bearings Inc. (MBI), a subsidiary of Kollmorgan Corporation was formed and licenced by S2M tomanufacture magnetic bearings in the Western Hemisphere. The first magnetic bearing installation took place in October, 1985. It yielded the world's first oil free mainline compressor unit. This unit is an Ingersoll-Rand CDP 230, 10 444 kW ISO compressor with a 1590 kg shaft and a 5440 kg thrust load. There are currently over 10 000 operating hours on this combined mechanical seal/magnetic bearing installation (Fig. la). Mechanical Dry Gas Seal Operating Principle The mechanical dry seal design is based on technology originally developed for air bearings.

Contacting mechanical seal design using a simplified hydrostatic model

While hydrostatic theory of mechanical face seal operation is well understood, there has always been some difficulty in applying this idea to the design of seals that contact. In this paper, a simple mixed friction model of seal load support is formulated. Surface roughness is an essential parameter. Mechanical contact load support and hydrostatic load support are both considered. Load support equilibrium is always satisfied. The minimum film thickness and leakage are found. Considering both fluid and mechanical contact friction, the total power consumption is found. The model works equally well for convergent or divergent films. This model is combined with both thermally—caused and pressure—caused radial taper effects using a simple relationship. Using very few algebraic equations, one can solve for the equilibrium operating conditions for practical seals. Design guidelines concenrning balance ratio, presure rotation coefficient, thermal rotation coefficient, and initial taper are developed by studying various nondimensional parameters which arise from this simple model. Typical seal performance is predicted and compared to some experimental data. The model can be easily used by others and provides immediate and practical results for seal design.