The Importance of Effective Sealing
Sealing is one of the most effective means to solve leakage problems in hydraulic systems. When a hydraulic system is not properly sealed, external leakage can contaminate the environment, and air can enter the hydraulic system, affecting the performance of the hydraulic pump and the smoothness of movement of hydraulic actuators. Understanding the differences in transmission fluid vs hydraulic oil is crucial here, as each has distinct properties that affect sealing requirements.
When internal leakage is severe, it causes过低的系统容积效率 and excessive oil temperature rise, leading to system malfunction. The choice between transmission fluid vs hydraulic oil can significantly impact these factors, as their viscosity and thermal properties differ under operating conditions. Proper sealing must account for these differences to maintain system integrity.
I. Requirements for Sealing Devices
Sealing Performance
Within the operating pressure and a certain temperature range, it should have good sealing performance, and the sealing performance should automatically improve as pressure increases. This is particularly important when considering transmission fluid vs hydraulic oil, as their different characteristics require adaptable sealing solutions.
Low Friction
The friction force between the sealing device and moving parts should be small, and the friction coefficient should be stable. The interaction between seal materials and different fluids, including the consideration of transmission fluid vs hydraulic oil, directly affects friction characteristics.
Durability
It should have strong corrosion resistance, be resistant to aging, have a long service life, good wear resistance, and be able to automatically compensate to a certain extent after wear. Compatibility with both transmission fluid vs hydraulic oil is essential for ensuring long-term durability.
Practical Design
The structure should be simple, easy to use and maintain, and inexpensive. A practical design must accommodate the specific properties of the fluid being used, whether considering transmission fluid vs hydraulic oil, to ensure optimal performance and ease of maintenance.
II. Types and Characteristics of Sealing Devices
Seals can be divided into non-contact seals and contact seals according to their working principles. The former mainly refers to clearance seals, while the latter refers to sealant seals. The choice between these types often depends on factors including operating pressure, temperature, and the specific fluid being used, making the understanding of transmission fluid vs hydraulic oil properties essential for proper selection.
1. Clearance Seals
Clearance seals rely on a small gap between the mating surfaces of relatively moving parts for sealing. They are commonly used in cylindrical mating pairs such as plunger pistons or valves. The performance of clearance seals can be affected by fluid viscosity differences, which is why understanding transmission fluid vs hydraulic oil characteristics is important.
Hydraulic valves using clearance seals have several equidistant pressure equalizing grooves on the outer surface of their spools. Their main function is to make the radial pressure distribution uniform, reduce hydraulic clamping force, and at the same time make the spool well centered in the hole. Clearance seals reduce leakage by reducing the gap.
In addition, the resistance formed by the pressure equalizing groove also plays a certain role in reducing leakage. The size of the pressure equalizing groove is generally 0.3-0.5mm in width and 0.5-1.0mm in depth. The fit clearance between cylindrical surfaces is related to the diameter. For valve cores and valve holes, it is generally 0.005-0.017mm.
The advantage of this seal is low friction, but the disadvantage is that it cannot automatically compensate after wear. It is mainly used for cooperation between cylindrical surfaces with small diameters, such as between the plunger and cylinder block in hydraulic pumps, and between the spool of slide valves and valve holes. When considering transmission fluid vs hydraulic oil, the smaller clearances may require more careful fluid selection to prevent excessive wear.
Key Characteristics of Clearance Seals
- Relies on precise manufacturing tolerances and surface finishes
- Low friction makes them suitable for high-speed applications
- Sensitive to fluid viscosity differences, such as those between transmission fluid vs hydraulic oil
- Requires careful consideration of thermal expansion effects
2. O-ring Seals
O-rings are generally made of oil-resistant rubber and have a circular cross-section. They have good sealing performance, and can seal the inner, outer and end faces. They feature a compact structure, low friction resistance of moving parts, ease of manufacture, convenient assembly and disassembly, low cost, and can be used in both high and low pressure applications.
O-rings are widely used in hydraulic systems. Their compatibility with various fluids, including considerations in transmission fluid vs hydraulic oil applications, makes them versatile sealing solutions across many industries.
The structure and working conditions of O-rings are shown in Figure 6-15. Figure 6-15a shows the outline drawing of the O-ring; Figure 6-15b shows the situation when it is installed in the sealing groove, where 8 and 6 are the pre-compression amounts of the O-ring after assembly, usually expressed by the compression rate, that is:
Compression Rate = (Original Diameter - Compressed Diameter) / Original Diameter × 100%
For static seals, reciprocating motion seals and rotary motion seals, the compression rates should reach 15%-20%, 10%-20% and 5%-10% respectively to obtain satisfactory sealing effects. When the oil working pressure exceeds 10MPa, the O-ring is easily squeezed into the gap by the oil pressure during reciprocating motion, as shown in Figure 6-15c.
For this reason, a 1.2-1.5mm thick PTFE retaining ring should be placed on its side. When受力 unidirectionally, a retaining ring is placed on the opposite side of the force-bearing side. When受力 bidirectionally, a retaining ring is placed on each side, as shown in Figures 6-15d and e. The compatibility of these materials with different fluids, including transmission fluid vs hydraulic oil, must be considered for optimal performance.
O-ring Applications and Considerations
- Available in various materials to accommodate different fluids, including specific formulations for transmission fluid vs hydraulic oil
- Cost-effective solution for both static and dynamic applications
- Require proper groove design for optimal performance
- Need backup rings in high-pressure applications (above 10MPa)
In addition to rectangular shapes, the installation grooves for O-rings also include V-shaped, dovetail-shaped, semicircular, triangular, etc. In practical applications, relevant manuals and national standards can be consulted. The choice of groove design may also be influenced by the specific fluid being sealed, with considerations for transmission fluid vs hydraulic oil playing a role in certain specialized applications.
3. Lip Seals
Lip seals can be divided into Y-shaped, V-shaped, U-shaped, L-shaped, etc. according to the shape of their cross-sections. Their working principle is shown in Figure 6-16. Hydraulic pressure presses the two lips h of the seal against the two part surfaces forming the gap.
The characteristic of this sealing effect is that it can automatically adjust the sealing performance with changes in working pressure. The higher the pressure, the tighter the lips are pressed, and the better the sealing performance. When the pressure decreases, the degree of lip compression also decreases, thereby reducing friction resistance and power consumption. In addition, it can automatically compensate for lip wear.
Currently, small Y-shaped seals are widely used in hydraulic cylinders, mainly for piston and piston rod sealing. Figure 6-17a shows the shaft seal, and Figure 6-17b shows the hole seal. The small Y-shaped seal is characterized by a large ratio of cross-sectional width to height, which increases the width of the bottom support and can avoid seal flipping and distortion caused by friction.
In high-pressure and ultra-high pressure situations (pressure greater than 25MPa), V-shaped seals are mostly used for shaft sealing. V-shaped seals are made of multi-layer rubberized fabric pressed together, and their shape is shown in Figure 6-18. V-shaped seals are usually used in a stack of three rings: pressure ring, seal ring and support ring, which can ensure good sealing performance. When the pressure is higher, the number of intermediate seal rings can be increased. These seals should be pre-tightened during installation, so the friction resistance is relatively large.
When installing lip seals, their lip opening should face the hydraulic oil, so that the two lips open and adhere to the surface of the machine parts respectively. The interaction between the lip material and the fluid, including considerations in transmission fluid vs hydraulic oil applications, is crucial for ensuring proper sealing and longevity.
Y-shaped Seals
- Excellent for both rod and piston sealing
- Good pressure activation characteristics
- Available in various materials for compatibility with transmission fluid vs hydraulic oil
- Resistant to extrusion in moderate pressure applications
V-shaped Seals
- Ideal for high-pressure applications (above 25MPa)
- Modular design allows for pressure range adjustment
- Multi-layer construction provides enhanced durability
- Higher friction due to preload requirement
4. Combined Sealing Devices
With the advancement of technology and the improvement of equipment performance, hydraulic systems have increasingly higher requirements for sealing. Ordinary seals used alone can no longer meet the needs well. Therefore, combined sealing devices composed of two or more components including seals have been researched and developed. These advanced sealing solutions often address the specific challenges presented by different fluid characteristics, such as those encountered when comparing transmission fluid vs hydraulic oil.
Advantages of Combined Sealing Systems
- Enhanced performance compared to single-component seals
- Can accommodate wider temperature and pressure ranges
- Improved resistance to fluid incompatibilities when considering transmission fluid vs hydraulic oil
- Reduced maintenance requirements through optimized design
- Better adaptation to dynamic operating conditions
III. New Types of Sealing Elements
With the development of the material industry and the improvement and development of sealing theory, many new types of sealing elements have been developed at home and abroad in recent years. These sealing elements have not only significantly improved in physical, chemical, and sealing properties, but also have undergone great changes in structure. Their functions have also developed from single-type to combined-type. Below are eight new types of sealing elements, each designed to address specific challenges, including those related to fluid characteristics in transmission fluid vs hydraulic oil applications.
1. Star Seals
Figure 6-21 shows a star seal, also known as an X-shaped seal, which is suitable for two-way sealing of hydraulic and pneumatic actuators. Star seals achieve sealing through the combined action of pre-compression force and oil extrusion force.
Star seals are suitable for linear, rotary dynamic seals and static seal occasions with pressure not greater than 40MPa, temperature of -60-200℃, and operating speed not greater than 0.5m/s. Their versatile design makes them suitable for various fluid applications, with material options available for both transmission fluid vs hydraulic oil compatibility.
2. Zurcon-Rem Seals
Zurcon-Rem seals are one-way seals, so they must be used in pairs to achieve two-way sealing. Zurcon-Rem seals are suitable for dynamic sealing occasions of shafts and holes with pressure less than 25MPa, temperature of -30-100℃, and operating speed of 5m/s for linear reciprocating motion, as shown in Figure 6-22. These seals are engineered with material formulations that consider the differences between transmission fluid vs hydraulic oil, ensuring optimal performance across various applications.
Comparative Characteristics of Modern Seal Materials
| Seal Type | Temperature Range (°C) | Max Pressure (MPa) | Fluid Compatibility |
|---|---|---|---|
| Star Seals | -60 to 200 | 40 | Good for both transmission fluid vs hydraulic oil |
| Zurcon-Rem Seals | -30 to 100 | 25 | Excellent for hydraulic oil, good for transmission fluid |
| O-rings (Nitrile) | -40 to 120 | 30 (with backup rings) | Good for hydraulic oil, limited for transmission fluid |
| V-shaped Seals | -20 to 100 | 70+ | Depends on material, generally good for both transmission fluid vs hydraulic oil |
Advanced Sealing Technology Considerations
Material Selection Criteria
The selection of sealing materials is critical to performance and longevity. Factors include temperature range, pressure rating, chemical compatibility, and dynamic characteristics of the application. When evaluating transmission fluid vs hydraulic oil, material compatibility becomes even more important, as certain elastomers may perform well with one fluid but poorly with another.
Common materials include nitrile rubber (NBR), fluorocarbon rubber (FKM/Viton), ethylene propylene diene monomer (EPDM), and polytetrafluoroethylene (PTFE). Each has distinct properties that make them suitable for specific applications, with varying performance when exposed to transmission fluid vs hydraulic oil.
Installation Best Practices
Proper installation is essential for optimal seal performance. Even the highest quality seals will fail prematurely if installed incorrectly. This includes ensuring proper groove dimensions, surface finishes, and avoiding damage during installation.
For dynamic applications, consideration must be given to the fluid's characteristics, such as the differences between transmission fluid vs hydraulic oil, which can affect friction, wear rates, and overall system performance. Proper lubrication during installation, using the same fluid that will be present in the system, is generally recommended.
Seal Failure Modes and Prevention
Understanding common seal failure modes is key to selecting the right seal and maintaining system performance. Common failure modes include extrusion, abrasion, chemical attack, and compression set. Each of these can be influenced by fluid characteristics, making the knowledge of transmission fluid vs hydraulic oil properties invaluable in troubleshooting and prevention.
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Extrusion: Occurs when seal material is forced into clearance gaps under pressure. Prevented by using appropriate backup rings and ensuring proper clearance for the application pressure.
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Abrasion: Caused by particulate contamination or rough surfaces. Prevented by proper filtration and ensuring surface finishes meet specifications.
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Chemical Attack: Results from incompatibility between seal material and fluid. Prevented by proper material selection based on fluid type, such as understanding transmission fluid vs hydraulic oil differences.
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Compression Set: Happens when a seal loses its ability to return to original shape after long-term compression. Prevented by selecting materials with appropriate compression set resistance for the application temperature and duration.
Conclusion
Effective sealing is fundamental to the performance, efficiency, and reliability of hydraulic systems. From basic clearance seals to advanced combined sealing devices, the proper selection depends on numerous factors including pressure, temperature, movement type, and fluid characteristics. Understanding the differences between transmission fluid vs hydraulic oil is essential in this selection process, as each fluid interacts differently with seal materials and designs.
As hydraulic systems continue to evolve, so too do sealing technologies, with new materials and designs offering improved performance across wider operating ranges. Proper maintenance and installation practices further ensure that sealing systems perform optimally throughout their service life.