This is filled with a liquid or solid (grease type) lubricant in order to avoid sliding friction. When the bearing journal reaches a sufficient circumferential speed, the bearing clearance allows the lubricant to form a load-bearing wedge. The lubrication wedge separates the sliding faces from one another, meaning that the bearing is operating on full lubrication. This process is typical of hydrodynamic plain bearings.

Hydraulic seals are designed to absorb large forces from the pressurized hydraulic medium, but may be sensitive to transverse, crushing, and shear forces. Guide rings absorb such forces and align the rod or piston centrally, so that wedging, scratching, scoring of the metallic components and destruction of the hydraulic seal by crushing or tearing can be avoided.

Rollingbearing

The hydraulic piston seal distinguishes two categories, depending on whether the piston is loaded from only one side (single-acting piston seal) or is subjected to pressure loads from both sides (double-acting piston seal).

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In this article, we want to introduce you to the foundations of hydraulic sealing, rod seals, and piston seals . Essential for efficient operational life are also wipers and guide elements, whose function, as well as profile and material options, we will explain in this article. We will also discuss individual sealing systems, since these are often the best choice in sealing technology. Learn about all the information on seals for various industries.

Plain bearings whose lubricant does not exhibit purely laminar flow characteristics (i.e. bearings with very high speeds and simultaneously very low lubricant viscosities tend to have a higher load-bearing capacity, but also higher friction losses. Here, the qualitative difference between a laminar and a turbulent flow plays a decisive role, alongside the characteristic coefficients for plain bearings already mentioned. Designing plain bearings with turbulent lubricant flow is much more complicated than designing bearings with laminar lubricant flow.

If sealing is not required in a pressureless state, rod seals can be installed without pre-pressing. In operation, system pressure pushes the wiper ring against the sealing surfaces, ensuring proper tightness.

Depending on the field of application, guide elements can be designed as a guide ring or guide band. There are a wide variety of geometries and several materials to choose from.

Hydrodynamic and hydrostatic types can be combined. In the case of plain bearings which operate hydrodynamically in the steady state, the increased friction during start-up and run-down and the wear associated with it can be reduced by providing auxiliary hydrostatic lubrication at a high pressure via longitudinal grooves which do not extend to the edge of the bearing shell.

The plain bearing is an element frequently used in centrifugal pump construction that allows a moving component to slide within a stationary component. A distinction is made between radial plain bearings for radial forces (transverse forces) and axial (or thrust) plain bearings for axial forces (longitudinal forces). See Fig. 1 Plain bearing

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Typically, rod seals are asymmetrical wiper rings whose shortened inner seal lip dynamically seals against the piston rod. The outer seal lip maintains static contact with the cylinder head. Due to the design, it's possible to apply pressure load from only one side, thus they are referred to as single-acting seals.

Rod seals seal the exit point of the piston rod from the cylinder. They are stationary in the housing, sealing statically with their outer ring. Internally, dynamic sealing occurs towards the movable rod.

Previously, elastomer O-rings and groove rings with thin sealing lips (conically tapering) were used, but these designs have become obsolete. Modern groove rings boast an optimal sealing lip profile, whose oil-side wedge gap achieves an optimal opening angle for sufficient lubrication of the seal surface while minimizing leakage (too steep: no lubrication film; too flat: thick lubrication film). This form of the sealing lips significantly enhances performance regarding stripping capability and retraction efficiency, especially under high pressure.

In general, hydraulic seals separate a pressurized fluid from its surroundings. In this case, the sealing gap is located between a moving piston and the housing or cylinder. The hydraulic seal has the following functions:

Whether standard electric motor or highly specialized electric drive - deep groove ball bearings are often the most suitable type of rolling bearing.

Guide element seals allow the straight retraction and extension of the hydraulic rod and prevent occurring transverse forces from leading to contact with the metallic parts or other damage in the hydraulic system.

Thrustbearing

Groove rings are fundamentally circular sealing elements that feature a groove, or an elongated indentation, along their diameter. This groove limits the two sealing lips that create the sealing edges for static and dynamic sealing. Depending on the application area (inner-sealing rod seals or outer-sealing piston seals), either the inner lip or the outer lip is shortened. The precise geometry of the sealing lips greatly affects the seal's effectiveness in terms of tightness and leakage rate.

It is important to differentiate groove rings from so-called compact rings, where the space between the sealing edges is filled with elastomer.

Rolling elementbearing

Appropriate rotor bearing design allows both types of lateral rotor vibrations (forced and self-induced) to be eliminated or reduced to an acceptable level for the machine. The dynamic bearing coefficients can be optimised. The choice of bearings is a key element of this optimisation, as each bearing offers different performance characteristics.A bearing clearance is achieved through the appropriate sizing and mutual adjustment of both the moving and stationary bearing components.

In engineering, hydraulic seals are essential components of numerous modern machines. A hydraulic seal isolates components or chambers within a machine from each other, as well as the interior of a machine from its environment. They prevent the ingress of air, moisture, and dirt, as well as the escape of gases and liquids. High-quality seals for the industry and trade are therefore indispensable. The transmission medium in hydraulics is water (or oil), in contrast to pneumatics (pneumatic seal), which operates with air. Hydraulics, therefore, is the study of the flow behavior of various fluids in a hydraulic cylinder.

When using high-performance seals, it is particularly expedient to also install the corresponding matching guide elements, because premature wear or defect of such a seal is not economical.

Hydraulic sealing systems are deployed in particularly demanding applications that require high levels of sealing effectiveness and durability. In some cases, a single hydraulic seal may not provide enough power to meet specific requirements, such as extreme cold, heat, or significant contamination in the workplace.

Hydraulic seals fall into the category of dynamic seals. In general, a distinction is made between static seals, i.e. between stationary parts (for example in the case of flange connections) and dynamic seals, in which a component is typically in motion (e.g. in the case of rotating shafts or retracting and extending pistons in a cylinder). Shaft seal, rotary seals and seal ring.

As a machine runs down, the plain bearings undergo the same process as described above for start-up, but in the reverse order (see Start-up process).

Fibre-reinforced ceramic bearings are being used more and more frequently due to their ability to resist tension and fractures. See Fig. 6 Plain bearing

The design of hydrodynamic plain bearings involves the solution of a complex problem which takes into account a number of factors such as bearing geometry and size, bearing load, the lubricant's viscosity the sliding velocity, the nature of the flow in the bearing (see Fluid mechanics) and the interaction between these factors.

Sphericalplain bearing

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Single-acting piston seals are similar in principle to rod seals, with the difference that in single-acting piston seals the outer diameter seals dynamically, while the inner diameter sits statically on the piston (i.e. an inverse arrangement of the stationary and moving components).

In such scenarios, a multi-component sealing system is advisable, with each component's functionality complementing the others. A sealing system, for example, may comprise one or more hydraulic seals along with guiding elements and wipers. Given the extensive variety of combination possibilities, we are keen to offer personalized consultation to create the ideal sealing system tailored to your application needs.

Many pumps are equipped with shaft guide bearings which are lubricated by the fluid handled. In these cases the choice of bearing materials is especially important as each fluid has its own characteristics as a lubricant. If clean water is used as a lubricant, several bearing materials with suitable tribological properties are available. These include metallic alloys, elastomers, hard rubber, electro-graphite with or without resin binders, hard graphite with or without resin binders or antimony impregnation.

Solve offers the widest assortment of mounted bearings and ball bearing inserts in the industry. We stock popular Metric and American Standard configurations.

Depending on the required performance, sealing rings with rubber lips or special so-called double scrapers are used in hydraulics. Double scrapers have two sealing edges. The inner, oil-side sealing edge wipes off excess hydraulic fluid and leaves a sufficient lubricating film when extended. The outer sealing edge removes impurities from the retracting rod.

We are experienced experts and can manufacture the hydraulic seals that are tailor-made for your requirements and areas of application.

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Our product range includes seals for hydraulic and pneumatic systems, among others, as well as specialized seals (with article numbers), spare parts, support rings, thread sealing (thread), and flat seals. Additionally, we provide high-performance materials such as Viton® and elastomers. At Kofler - Dichtungen, you can purchase your hydraulic seals or contact us for expert advice tailored to your needs.

We supply various sectors with our seals: construction, food industry, wood industry, energy technology, tunnel construction and agricultural and municipal technology.

They have a symmetrical contact pressure curve and react extremely quickly to the pressure of the hydraulic medium. Here, too, depending on the area of application, pre-compression (installation under pressure, tension) may be necessary. This is achieved by the dimension and geometry of compact rings or by elastomeric O-rings. Our assembly tool for hydraulic seals is ideally suited for the installation of these seals.

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This pre-loading can be achieved through the shape (e.g., compact rings) or multi-part seals (e.g., groove ring + O-ring or groove ring + spring). These seals also have sufficient sealing pressure without system pressure to prevent leakage.

As the sliding velocity increases further, the thickness of the lubricant film also increases, but friction losses rise again slightly. See Fig. 5 Plain bearing

Accordingly, these single-acting piston seals such as rod seals are designed as asymmetrical groove rings, except that the outer, dynamically locking sealing lip is shortened.

All three friction types can occur in hydrodynamic plain bearings during the three phases of operation: start-up, operation, run-down. Start-up is the operating phase from standstill to full operating speed. As the sliding velocity increases, hydrodynamic plain bearings experience mixed friction, with the amount of dry friction gradually giving way to fluid friction as speed increases further. Finally the transition point is reached when the surfaces separate from one another and full fluid film lubrication with a minimum of friction losses is established.

The plain bearing is an element frequently used in centrifugal pump construction that allows a moving component to slide within a stationary component. A distinction is made between radial plain bearings for radial forces (transverse forces) and axial (or thrust) plain bearings for axial forces (longitudinal forces). See Fig. 1 Plain bearingRadial plain bearingOn radial plain bearings, the moving part is the pin or journal of the axle or shaft; the stationary part is the bearing shell.Bearing shells and other variantsa Cylindrical bearing shellsee Fig. 2 a Plain bearingb Two-face, lemon-bore bearing shellsee Fig. 2 b Plain bearingc Two-face, radially offset bearing shellsee Fig. 2 c Plain bearingd Three-face bearing shellSee Fig. 2 d Plain bearinge Three-face and multiple-face bearing shell with lubrication grooves or pocketssee Fig. 2 e Plain bearingf Rubber bearingsee Fig. 2 f Plain bearingg Multiple-face bearing with tilting radial padssee Fig. 2 g Plain bearingThis wide range of bearing designs is required to cater for the dynamic operating behaviour characteristic of centrifugal pump rotors. The vibration characteristics of rotors fitted with plain bearings depend largely on the rotor mass, the mass distribution, the shaft stiffness and the dampening characteristics of the bearings at a given load.Appropriate rotor bearing design allows both types of lateral rotor vibrations (forced and self-induced) to be eliminated or reduced to an acceptable level for the machine. The dynamic bearing coefficients can be optimised. The choice of bearings is a key element of this optimisation, as each bearing offers different performance characteristics.A bearing clearance is achieved through the appropriate sizing and mutual adjustment of both the moving and stationary bearing components.This is filled with a liquid or solid (grease type) lubricant in order to avoid sliding friction. When the bearing journal reaches a sufficient circumferential speed, the bearing clearance allows the lubricant to form a load-bearing wedge. The lubrication wedge separates the sliding faces from one another, meaning that the bearing is operating on full lubrication. This process is typical of hydrodynamic plain bearings.Advantages and disadvantages of hydrodynamic plain bearingsAdvantages:Simple manufacture; the lubricant is fed either unpressurised or at very low feed pressure into the bearing during operationVery little or no energy is required for the oil supply systemDisadvantages:During start-up and run-down, full fluid film lubrication is impossible, resulting in wear on the running surfaces (mixed friction) see Fig. 4 Plain bearingAnother bearing type is the hydrostatic plain bearing. Here, the liquid lubricant is fed into the individual bearing pockets under high pressure. Forces are absorbed as a result of pressure differences:High static pressure in the pockets on the loaded side of the running surface (small clearance during operation, therefore very small decrease in pressure in the lubricant layer)Low static pressure in the pockets of the unloaded side of the running surface (large clearance during operation, therefore considerable pressure drop in the lubricant layer)Advantages and disadvantages of hydrostatic plain bearings:Advantage: full fluid film lubrication at all times, including start-up and run-down, therefore no excessive wear riskAdvantage: smaller dimensions and lower friction losses in comparison with hydrodynamic bearings of equal load-bearing capacityDisadvantage: more expensive to manufacture than hydrodynamic plain bearings (several manufacturing operations)Disadvantage: more expensive to operate because pressure boosting is required for the lubricant, leading to increased investment and energy costsHydrodynamic and hydrostatic types can be combined. In the case of plain bearings which operate hydrodynamically in the steady state, the increased friction during start-up and run-down and the wear associated with it can be reduced by providing auxiliary hydrostatic lubrication at a high pressure via longitudinal grooves which do not extend to the edge of the bearing shell.The auxiliary lubricant feed is shut off during normal operation to ensure that the hydrodynamic pressure is maintained in the lubricating clearance gap.Friction conditions in a plain bearingSee Fig. 3 Plain bearing:a. Dry friction:     without a separating lubricant layer between the stationary and moving componentsb. Mixed friction:    a combination of dry and fluid frictionc. Fluid friction:   with a separating lubricant layer (ideal situation)All three friction types can occur in hydrodynamic plain bearings during the three phases of operation: start-up, operation, run-down. Start-up is the operating phase from standstill to full operating speed. As the sliding velocity increases, hydrodynamic plain bearings experience mixed friction, with the amount of dry friction gradually giving way to fluid friction as speed increases further. Finally the transition point is reached when the surfaces separate from one another and full fluid film lubrication with a minimum of friction losses is established.As the sliding velocity increases further, the thickness of the lubricant film also increases, but friction losses rise again slightly. See Fig. 5 Plain bearingThis frictional behaviour was the subject of research by Stribeck. See Fig. 4 Plain bearingAs a machine runs down, the plain bearings undergo the same process as described above for start-up, but in the reverse order (see Start-up process).A plain bearing should generally have its steady-state operating point during the full fluid film lubrication phase. If mixed friction is present during continuous operation, excessive wear at the bearing faces can be expected. Particular care should be taken to correctly select and match the two materials whose surfaces require lubrication (wear, heat dissipation).Many pumps are equipped with shaft guide bearings which are lubricated by the fluid handled. In these cases the choice of bearing materials is especially important as each fluid has its own characteristics as a lubricant. If clean water is used as a lubricant, several bearing materials with suitable tribological properties are available. These include metallic alloys, elastomers, hard rubber, electro-graphite with or without resin binders, hard graphite with or without resin binders or antimony impregnation.If the fluid handled is used as a lubricant and is dirty or contains solids such as sand, the bearing materials should be made from hard metals or ceramic materials (e.g. silicon carbide). Using the same material for bearing bushes and shaft protecting sleeves results in a maintenance-free bearing.Fibre-reinforced ceramic bearings are being used more and more frequently due to their ability to resist tension and fractures. See Fig. 6 Plain bearingFriction is converted into heat which is partly dissipated to the surrounding air via the bearing housing or the shaft. The plain bearing should therefore not exceed the max. bearing operating temperature. If necessary, a cooling system must be provided for the bearing or lubricant (usually water cooling).The design of hydrodynamic plain bearings involves the solution of a complex problem which takes into account a number of factors such as bearing geometry and size, bearing load, the lubricant's viscosity the sliding velocity, the nature of the flow in the bearing (see Fluid mechanics) and the interaction between these factors.The objective of plain bearing design is to ensure that full fluid film lubrication can be reliably achieved during operation. The design process incorporates theoretical principles and experimental data, taking into account multiple interrelated characteristic coefficients (i.e. those relating to radial plain bearings): see Fig. 7 Plain bearingPlain bearings whose lubricant does not exhibit purely laminar flow characteristics (i.e. bearings with very high speeds and simultaneously very low lubricant viscosities tend to have a higher load-bearing capacity, but also higher friction losses. Here, the qualitative difference between a laminar and a turbulent flow plays a decisive role, alongside the characteristic coefficients for plain bearings already mentioned. Designing plain bearings with turbulent lubricant flow is much more complicated than designing bearings with laminar lubricant flow.Axial (thrust) plain bearingThe moving part of an axial (thrust) plain bearing is the thrust collar or plate.Stationary part and its variantsSee Fig. 8 Plain bearing:Thrust bearing ringThrust bearing ring with machined wedge facesThrust bearing ring with stepped damming gapEccentrically supported tilting pads or often centrally supported tilting pads (e.g. where a cooling water pump has to rotate in reverse (turbine mode) because of a backflow from the piping)Depending on the design axial (thrust) plain bearings are subdivided into hydrodynamic, hydrostatic and combined hydrostatic-hydrodynamic plain bearings for special applications. Both basic design types must allow sufficient axial shaft movement to accommodate the lubricant film thickness, which varies according to load, viscosity of the lubricant, and sliding velocity. The same arguments as for radial plain bearings apply to the advantages and disadvantages of hydrodynamic versus hydrostatic axial (thrust) plain bearings. Fig. 9 Plain bearing illustrates a product-lubricated carbon bearing in a circulating pump.Â

Another bearing type is the hydrostatic plain bearing. Here, the liquid lubricant is fed into the individual bearing pockets under high pressure.Â

The auxiliary lubricant feed is shut off during normal operation to ensure that the hydrodynamic pressure is maintained in the lubricating clearance gap.

We will be happy to advise you in order to be able to manufacture the optimal hydraulic seals for your area of application.

Typically, scrapers are made of NBR (nitrile butadiene rubber), PU (polyurethane) or PTFE (polytetrafluoroethylene). With this range of materials, a wide area of applications can be covered in terms of temperature range, system pressure and hydraulic fluid.

If the fluid handled is used as a lubricant and is dirty or contains solids such as sand, the bearing materials should be made from hard metals or ceramic materials (e.g. silicon carbide). Using the same material for bearing bushes and shaft protecting sleeves results in a maintenance-free bearing.

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A plain bearing should generally have its steady-state operating point during the full fluid film lubrication phase. If mixed friction is present during continuous operation, excessive wear at the bearing faces can be expected. Particular care should be taken to correctly select and match the two materials whose surfaces require lubrication (wear, heat dissipation).

On radial plain bearings, the moving part is the pin or journal of the axle or shaft; the stationary part is the bearing shell.

The double-acting piston seal (hydraulic systems with differential cylinders between two pressure ranges) can be pressure-loaded from both sides, i.e. it separates two chambers from each other, both of which can alternately be under overpressure. Such double-acting piston seals are typically designed as symmetrical groove rings or compact rings.

In addition, there is also the hydrostatic field of application, in which the seals must ensure that, for example, a cylinder must remain in the same position for a longer period of time.

Are you looking for complete hydraulic cylinder seal sets and seals? We at Kofler - Dichtungen offer standard sealing sets or custom-made products. We can also develop and mass-produce gasket sets of the gaskets below for you and your applications.

The objective of plain bearing design is to ensure that full fluid film lubrication can be reliably achieved during operation. The design process incorporates theoretical principles and experimental data, taking into account multiple interrelated characteristic coefficients (i.e. those relating to radial plain bearings): see Fig. 7 Plain bearing

Depending on the design axial (thrust) plain bearings are subdivided into hydrodynamic, hydrostatic and combined hydrostatic-hydrodynamic plain bearings for special applications. Both basic design types must allow sufficient axial shaft movement to accommodate the lubricant film thickness, which varies according to load, viscosity of the lubricant, and sliding velocity. The same arguments as for radial plain bearings apply to the advantages and disadvantages of hydrodynamic versus hydrostatic axial (thrust) plain bearings. Fig. 9 Plain bearing illustrates a product-lubricated carbon bearing in a circulating pump.

Friction conditions in a plain bearingSee Fig. 3 Plain bearing:a. Dry friction:     without a separating lubricant layer between the stationary and moving components

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Sleevebearingoil ring

A hydraulic cylinder seal set consists of several seals that are used in hydraulics. In the best case, all individual sealing elements work in harmony. It is important to coordinate the seal for hydraulic applications. The respective materials used play a decisive role in determining whether the entire hydraulic cylinder seal set works in the long term. The seals for the hydraulics are divided into piston seals, rod seals, rotary seals, grooved rings, scrapers and guide rings.

If sealing in the pressureless state is also necessary (e.g., to prevent the hydraulic fluid from leaking during storage or transport of the device), a seal with pre-pressing (installed under tension or pressure) must be used.

Scrapers are located behind the actual hydraulic seal. These are components that are in principle not exposed to any significant pressure load. Wipers have a dual function: on the one hand, they wipe dirt, dust, water and other impurities from the retracting rod to avoid contamination of the hydraulic system. On the other hand, they must allow a thin film of oil on the rod to sufficiently lubricate the seal when retracting. A balance must be ensured here, because too large an amount of oil practically represents a leak and dirt adheres more easily to the oil layer.

Bearing

Groove rings are typically made from wear-resistant PU (polyurethane), low-friction, temperature- and chemical-resistant PTFE (polytetrafluoroethylene), or flexible, high-performance elastomers (NBR, nitrile butadiene rubber).

We will be happy to advise you in order to be able to manufacture the optimal hydraulic seals for your area of application.

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This wide range of bearing designs is required to cater for the dynamic operating behaviour characteristic of centrifugal pump rotors. The vibration characteristics of rotors fitted with plain bearings depend largely on the rotor mass, the mass distribution, the shaft stiffness and the dampening characteristics of the bearings at a given load.

Friction is converted into heat which is partly dissipated to the surrounding air via the bearing housing or the shaft. The plain bearing should therefore not exceed the max. bearing operating temperature. If necessary, a cooling system must be provided for the bearing or lubricant (usually water cooling).