Seal Life Research Articles

Miniature Air Compressor Design Based on Cross-Slider Mechanism

Most of the current air compressors are driven by a slider-crank mechanism consisted of the crank, connecting rod, and piston. Complexity of this mechanism, however, restricts miniaturization of air compressors. In this study, a design based on a new mechanism, a hybrid of cross-slider and scotch-yoke mechanism, is adopted to develop an oil-free, light-weighted air compressor for portable medical devices. By eliminating the connecting rod, the mechanism has several advantages in addition to the obvious weight reduction due to the simpler mechanism such as the longer seal life of the seal between the piston and cylinder (so called Teflon cup) and reduced shaking forces. Cylinder pressure time history is obtained based on the ideal gas behavior and the isentropic process. Shaking forces and motor torque are calculated from the dynamics equation of the air compressor. The flow capacity curve of the air compressor is obtained by considering the effect of the clearance volume. An actual prototype was fabricated and tested to demonstrate the feasibility of proposed concepts.

Failures due to ingested bodies in hydraulic turbines

The ingestion of large bodies in turbines can produce blockage in the runner that generates large, unbalanced forces. Blockage in the distributor can change the amplitude and uniformity of the pressure pulsations. Mechanical damage may also be generated. In all cases, the efficiency of the turbine is reduced and the forces on the runner and the vibration levels in the machine are greatly amplified, which reduces the expected life of bearings and seals and even produces considerable damage. In this paper, we present an overview of the damage caused by the ingestion of external bodies in hydraulic turbines. We describe some examples found during 20 years of monitoring. These types of failure have never been studied (except the typical sand erosion), as the grille of the trash rack should prevent the entrance of large bodies to the turbine. However, the trash rack is often partially broken and bodies may detach from the pipe lining. Some cases of damage due to the ingestion of small bodies and particles are also discussed.

New material extends life of offshore wind-turbine seals

New material extends life of offshore wind-turbine seals

First tests results for determination of seal life of EPDM O-rings at high temperature (determined by unique method)

A recurrent concern in the design of packaging for the transportation of radioactive material is to determine the life of elastomeric O-rings at a high temperature. Following a precedent paper presenting the TN International method for the determination of ethylene propylene diene (EPDM) O-rings seal life, a first series of tests results have been obtained. These first results are used with the previously mentioned method to see that the EPDM seal life did follow an Arrhenius curve. This Arrhenian behaviour is verified below a certain 'threshold temperature' that seems to be the upper limit for the use of such elastomeric O-ring grades. With the 'seal life versus temperature' curve obtained from these tests results, the time–temperature profile of O-rings in casks can then be benchmarked with the seal resistance and its 'maximum permissible damage rate'.

Slurry pump gland seal wear

Gland sealing research since the 1950s by BHRA and others has aimed at improving seal (leakage) performance. The principal focus has been on uniform packing compression to more closely match the packing pressure distribution with the fluid (medium) pressure thereby reducing leakage over time. Published research on shaft sleeve/packing wear and seal reliability has typically focussed on a slurry free environment. Should a gland seal process environment deviate from ideal then the system must be more robust to tolerate the ingress of slurry particles. It is postulated that non uniform packing compression is not the sole contributor to gland seal life cycle cost and reliability. An improved scientific understanding of the tribological wear process is required for existing designs. This will lead to lower life cycle cost and improved reliability for end users. In slurry service particle size distribution, shape, and relative hardness with the shaft sleeve are expected to influence the useful life of the shaft sleeve and packing. In this work findings from experimental testing are discussed and a new wear model is proposed.

Formation of transfer layer and its effect on friction and wear of carbon–graphite face seal under dry, water and steam environments

The present work aims to explore the friction and wear characteristics of antimony-impregnated-carbon–graphite material used in steam rotary joint and to study the transfer of graphite films from seals to mating metal surfaces. An experimental facility consisting of a 1.3 MPa capacity boiler to supply saturated steam, a torque sensor, a displacement sensor, two thermocouples, a data acquisition system, a bakelite coupling to insulate the torque sensor, a 2237 W (3 hp) A.C. motor with frequency drive to control the rotational speed of shafts, and actual rotary joint has been developed to measure the instant friction losses and calculate the wear loss of four seals used in rotary joint. Wear loss, friction torque and surface temperature of sealing surfaces have been measured under dry, water and steam lubrication conditions. The obtained results are tabulated and plotted for quick understanding of experimental findings. Discussions on the excessive wear rate due to the presence of abundant water, misalignment and closing force are presented. Finally design changes to enhance the seal life are recommended.

Harbour seal movements and haul‐out patterns: implications for monitoring and management

Abstract Compliance with conservation legislation requires knowledge on the behaviour, abundance and distribution of protected species. Seal life history is characterized by a combination of marine foraging and a requirement to haul out on a solid substrate for reproduction and moulting. Thus understanding the use of haul out sites, where seals are counted, as well as their at‐sea movements is crucial for designing effective monitoring and management plans. This study used satellite transmitters deployed on 24 harbour seals in western Scotland to examine movements and haul‐out patterns. The proportion of time harbour seals spent hauled out (daily means of between 11 and 27%) varied spatially, temporally and according to sex. The mean haul‐out duration was 5 h, with a maximum of over 24 h. Patterns of movement were observed at two geographical scales; while some seals travelled over 100 km, 50% of trips were within 25 km of a haul‐out site. These patterns are important for the identification of a marine component to designated protected areas for the species. On average seals returned to the haul‐out sites they last used during 40% of trips, indicating a degree of site fidelity, though there was wide variation between different haul‐out sites (range 0% to >75%). Low fidelity haul‐out sites could form a network of land‐based protected areas, while high fidelity sites might form appropriate management units. Copyright © 2008 John Wiley & Sons, Ltd.

New Kalrez extends seal life in hot, aggressive chemicals

New Kalrez extends seal life in hot, aggressive chemicals

Optimizing total system cost by balancing unit cost against real cost

Both pump manufacturers and chemical processors are reporting significant long-term savings from making initial investment in perfluoroelastomer seals, the most fluid resistant of elastomeric sealing materials, due to benefits in greatly reduced downtime and longer seal life. This can lead to increased productivity and lower environmental risk. This feature discusses how this may be approached and provides some examples of user experience.

New material extends seal life in aerospace applications

The newly engineered Turcon M30 non-abrasive material from Busak+Shamban has been shown to improve seal performance against tungsten carbide coated moving parts in primary flight controls and utility actuation systems.

Counter surfaces of hydraulic seals for heavy-duty applications

A detailed investigation of the effect of piston rod surface texture on seal performance has been carried out. This has shown that the use of R k parameters to control the presence of abrasive peaks on the surface can provide reduced wear and improved seal life.

Seal life of EPDM O-rings at high temperature determined by unique method

Abstract A recurrent concern in the design of packaging for the transport of radioactive material is to determine the life of the elastomeric O-ring at high temperature. Most O-ring suppliers specify maximum allowable temperatures during 'continuous service' and 'peak service' (such as '200°C in continuous service' or '250°C in peak') but they do not specify the definition of 'continuous' or 'peak' service, the acceptance criteria or how these maximum temperatures are determined. It is difficult on the basis of these types of data to assess the acceptability of an O-ring submitted to fluctuating temperatures. Cogema Logistics has launched a test programme to determine the maximum seal life at different temperatures (e.g. 200°C, 210°C,…, 250°C…) of the different rubber grades used on its casks, based on clearly defined criteria. The goal is to establish, for each rubber grade, the seal life versus temperature curve. These curves can be used to determine if an O-ring exposed to any specified temperature pro...

Recent progress in compressor sealing

Although the familiar dry gas seal is a well established method of sealing rotary compressors, new developments continue to be made available. This article discusses the benefits that can be obtained from bi-directional seal designs and describes their application, including compact designs for screw compressors. However, there are applications where it is still desirable to use a liquid lubricated gas seal, and modern designs can provide low oil leakage and long seal life.

CDR Pompe SpA gains over 2 years seal life with Kalrez Spectrum™ 6375 O-rings

CDR Pompe SpA gains over 2 years seal life with Kalrez Spectrum™ 6375 O-rings

Age, Sex, and Reproductive State Influence Free Amino Acid Concentrations in the Fasting Elephant Seal

Long-term fasting is a component of northern elephant seal (Mirounga angustirostris) life history requiring physiological adaptations to nitrogen conservation. Plasma free amino acids (FAAs) were determined for five elephant seal pups during the second and eighth weeks of the postweaning fast, six lactating female seals at 4-6 and 25 d postpartum, and seven sexually competitive adult male seals taken midway through the breeding season. Total FAAs declined in lactating females (11%) and pups (30%) with time fasting, but cystine concentration more than doubled in pups while decreasing by approximately 43% in lactating females. Methionine concentration significantly increased (approximately 68%) across lactation in adult females but was low for all classes of seal. Alanine was the most abundant FAA in adult males, and glycine became the dominant FAA in adult females late in lactation. Glutamine dominated the FAAs of weaned pups across the fast. Reductions in total FAAs of weanlings mirrored reductions in protein catabolism, but reductions in total FAAs also occurred in lactating females concomitant with an increase in protein catabolism. Observed variation in FAA concentrations may reflect ontogenetic requirements for certain amino acids in fasting weanlings. Similarly, increases in specific FAA concentrations across lactation may reflect variations in FAA flux resulting from the nutrient demands of lactogenesis.

Influence of elastomer compound design on the performance of rotary shaft lip seals

Spring-energized rotary shaft lip seals are widely accepted as efficient and cost-effective bearing seals. There is a trend towards increasing shaft speeds, the use of wear-resistant coatings and requirements to minimize seal leakage either for cost or environmental reasons while maximizing seal life. At present, higher surface speeds and improved sealing efficiency result in higher under-lip temperatures, limiting seal life and increasing seal friction. This feature discusses research conducted to investigate the effects of harsher operating conditions, and the development of a new elastomer compound with inherent heat dissipation properties and superior wear resistance without prohibitive increases in friction or cost. Material property data and functional test results from laboratory and field trials are discussed.

High-performance lift augmentation dynamic seals for turbine bearing compartments

Conventional bearing shaft seal systems used in gas turbine engines are often limited to a sliding velocity of about 100 m/s, differential pressure of 3 bar, gas temperature of 300°C and a seal life less than 8000 h. Advanced engines will require bearing shaft seal systems to operate up to sliding velocity of 200 m/s, differential pressure of 6 bar, gas temperature of 500°C and seal life in excess of 30 000 hours. For seals operating in these advanced conditions, a design with no rubbing contact will be required to achieve long life and reliability. A good validated approach is the use of a gas lift augmentation seal. The design objective for a seal of this type is to have the faces of the seal seek an equilibrium position to avoid any contact. The gap must be small enough to ensure a minimal air leakage, but it must be large enough to limit power dissipation, due to shear in the gas film, and face deformation by shaft displacement, misalignment and vibration. Dynamic seals for a bearing compartment have the following main functions: provide static and dynamic sealing in order to prevent oil leakage from the bearing oil compartment to the air compartment and consequently no oil smell pollution by the use of bleed air; control air leakage to the bearing oil compartment in order to improve performance of the engine and to reduce oil consumption; reduce volume of the oil tank and lubrication system and hence provide weight reduction; to operate in extreme conditions of temperature and with normal and reverse pressure; and reduce the mean time between overhaul (MTBO) and have a very long life. Techspace Aero and Burgmann have carried out design, development and testing of lift augmentation carbon seals and demonstrated that high life and performance levels of these seals are possible in a gas turbine engine environment.

Engineered material increases pump seal life from weeks to years

Engineered material increases pump seal life from weeks to years

Modern Approach to Reduce Pump Seal Life Cycle Cost in the United States

Modern Approach to Reduce Pump Seal Life Cycle Cost in the United States

Fundamental Design Issues of Brush Seals for Industrial Applications

Abstract Advanced seals have been applied to numerous turbine machines over the last decade to improve the performance and output. Industrial experiences have shown that significant benefits can be attained if the seals are designed and applied properly. On the other hand, penalties can be expected if brush seals are not designed correctly. In recent years, attempts have been made to apply brush seals to more challenging locations with high speed (>400 m/s), high temperature (>650 °C), and discontinuous contact surfaces, such as blade tips in a turbine. Various failure modes of a brush seal can be activated under these conditions. It becomes crucial to understand the physical behavior of a brush seal under the operating conditions, and to be capable of quantifying seal life and performance as functions of both operating parameters and seal design parameters. Design criteria are required for different failure modes such as stress, fatigue, creep, wear, oxidation etc. This paper illustrates some of the most important brush seal design criteria and the trade-off of different design approaches.