Every hydraulic system must use sealing. It improves the performance of a hydraulic system as well as prevents the leakage of fluids. Various industries perform a lot of applications using hydraulic seals. Industries that use hydraulic seals to reduce or eliminate fluid leakage are automotive manufacturing, aerospace manufacturing, defense contracting, agriculture, nuclear power and many others. Certain factors you should consider while selecting a hydraulic seal for any application is pressure, fluid type, temperature, and fluid chemical compatibility. Hydraulic seals are necessary for every industry to transfer fluids safely without having any leakage between two connecting parts.
The construction of hydraulic seals uses materials like polyurethane, PTFE, or rubber, which are relatively soft and non-metallic rings. Preventing leakage is an essential function of any hydraulic seal. It also protects the system from contamination and enhances the life span of hydraulic systems. Leakages of hydraulic systems are classified into internal leakage and external leakage. In internal leakage, the leaked fluids pass back again to the reservoir and do not result in fluid loss. Misalignment of fittings causes external leakages, which leads to poor performance due to fluid loss.
Static and dynamic are the major categories of hydraulic seals which are positive and negative based on the application it is used with. Positive seals do not allow any leakage, whereas; negative seals create some internal leakages. The use of a static seal is in between mating parts that do not have any relative motion. It assembles a simple and non-wearing joint by compressing two rigidly connected parts. Likewise, the use of a dynamic seal is between mating parts with relative motion. Dynamic seals can wear and tear due to the rubbing action of mating parts.
- Piston seal
Piston seals are internal to the cylinder head and seal against the cylinder bore. It prevents the fluid from flowing across the cylinder head. Due to this, the pressure builds on one side of the piston, making the cylinder retract or extend. It typically classifies as single-acting or double-acting. Single-acting means pressure acting on one side only and double-acting mean force acting on both sides of the seal.
- Rod seal
Rod seal is made using elastomeric material, which is like a ring located between the reciprocating cylinder and the cylinder wall. The job of rod seal is to keep the fluid contained within the cylinder while the rod retracts and extends. The operation of the hydraulic cylinder is critical, as it prevents fluid from escaping. It also allows the system to build the operating pressure required to move the actuator. Rod seals are made to maintain a thin film of liquid as the cylinder rod extends and retracts, which is essential to lubricate the rod, inhibit rod corrosion, and wiper seal.
- Buffer seal
Buffer seal protects the primary rod seal from huge pressure loads and spikes. It must permit sufficient lubrication to the central rod seal. It must also prevent the pressure to build up between the two. They are usually designed into hydraulic sealing systems in heavy-duty applications. It is placed on the piston seal to absorb the pressure during a stroke.
- Wiper seal
Wiper seals, also known as scraper seals, play a vital role in restricting the entry of external contaminants such as dust, moisture, and dirt to the hydraulic system or cylinder assemblies. The seals create a tight fit by permitting the passage of reciprocating ramrod through the inner bore of the seal. Typically, the polyurethane component is required to construct wiper seals.
- Symmetric seals
Symmetric seals are an alternative to the piston and rod seals, which uses simple linear operations. Symmetric seals are not ideal because of its fewer stability cycles with pumping and rocking effects. It is located in the gland with direct contact to the seal lips.
- Wear rings
Commonly, Wear ring retains piston centralized; it gives equal wear and stress allotment on the seals. The installation of piston and rod seals uses wear rings.
Conclusion
Hydraulic cylinder seals play a vital role. The relatively fragile components must deal with extreme exposure, heat, and pressure to chemicals and fluids. When you want to design a new cylinder and repair an existing unit, correct hydraulic seal selection is non-negotiable. Although suppliers recommend a highly controlled environment for seal installation, it is challenging to achieve in the fields. Designers must consider the likelihood that a damaged seal will need to be uninstalled and a new one to be installed in a less than ideal condition.
