Sealing is necessary for every hydraulic system we use. It prevents fluid leakage and improves the performance of every hydraulic system. You can find different types of hydraulic seals in various industries performing a lot of applications. Some of the common industries that utilizes hydraulic seals to limit or eliminate fluid leakage includes aerospace manufacturing, automotive manufacturing, agriculture, defence contracting, nuclear power, and more.. fluid type, pressure, fluid chemical compatibility or temperature are the factors that need to be considered while selecting a hydraulic seal for any application. In short, hydraulic seals are necessary for every industry for safe transferring of fluids without any leakage between the connecting parts.
Hydraulic seals are relatively soft, non-metallic rings that are constructed using materials such as polyurethane, rubber or PTFE. The important functions of hydraulic seals includes preventing leakage, protecting the system from contamination and thus improving the life span of hydraulic systems. Hydraulic system leakages are classified into internal leakage and external leakages. Internal leakages doesn’t results in fluid loss instead the leaked fluids are passed back to the reservoir. But, external leakages are caused by misalignment of fittings and will results in reduced performance due to the loss of fluids.
The major categories of hydraulic seals are positive and non-positive based on the application(static/dynamic) those are used with. Positive seals doesn’t permit any leakage. But, non-positive seals creates some internal leakages. Static seals are used in between mating parts that doesn’t have any relative motion. Those are a simple and non-wearing joint that are assembled between two rigidly connected parts by compressing. Similarly, dynamic seals are used between mating parts with relative motion. Due to the rubbing action of mating parts, dynamic seals are subjected to wear and tear.
More details on hydraulic seals types are discussed below.
Piston seal is a type of hydraulic seal where the sealing lip has contact with the entire housing bore. The immense clearance in between the machine’s piston and cylinder wall can be isolated and cover up with this seals. These seals are important for maintaining the piston position at rest and to control the motion of cylinder. The piston seals acts as a pressure barrier and prevent fluid from passing the piston.
Rod seals are commonly used static hydraulic seals for hydraulic cylinder sealing. Rod seals prevent rod corrosion and helps for the lubrication of wiper seal and rod seals. Together with the wiper seals, the rod seals can protect the system from external contaminants. The uses of rod seals vary from medium to high-duty applications with robust sealing effects.
Wiper seals or scraper seals plays an important role in preventing the entry of external contaminants such as moisture, dirt, and dust to the hydraulic system or cylinder assemblies. These seals create a tight fit by allowing the passage of reciprocating ramrod through the inner bore of the seal. Commonly, wiper seals are constructed using the component polyurethane.
Buffer seals are used in hydraulic systems with excess system pressure. These seals protects the rod seals from the damages caused as a result of pressure rise. The buffer seals attenuate the pressure fluctuations to improve the rod seal performance. Also, these seals protect the rod seals from contaminants.
Symmetric seals are an alternative to rod and piston seals and are used with simple linear operations. These seals are not widely recommended because of its less stability cycles with rocking and pumping effects. The symmetric seals are located in the gland with direct contact to the seal lips.
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