Hydraulic seals are a device that restricts the escape of fluid and foreign materials from entering in a hydraulic application such as a cylinder. When it comes to hydraulic seals, they are designed for high-pressure dynamic applications like hydraulic cylinders. Throughout different types of machinery, hydraulic seals are an essential piece to it functioning properly. Hydraulic seals can also be used for rotary and reciprocating motions.
Common Hydraulic Seals
Common hydraulic seals include: rod seals, piston seals, symmetrical seals, V-Rings, wipers, rotary shaft seals, wear rings, static seals, back-up rings, o-rings, buffer rings, u-cups, oil & grease seals, cast iron piston rings and gaskets. Hydraulic seals can be single or double acting. Single acting hydraulic seals are used for one axial direction only. Double acting hydraulic seals are used in both directions for a reciprocating motion. Hydraulic seals can be made of various materials including Nitrile, Polyurethane, FPM/Fluorocarbon rubber, silicone, PTFE, POM, EPDM, Nylon, bronze-filled PTFE, nickel-filled PTFE, and glass-filled PTFE. Some hydraulic seals can be molded of leather or fabric reinforced rubber.
Rod Seals are the most critical seals in a hydraulic cylinder. Rod Seals are radial internal seals. Rod Seals are press-fit into a housing bore with the sealing lip contacting the shaft. Rod Seals are also referred to as shaft seals sometimes. Rod Seal failure could result in fluid leakage. Special care should be shown in selecting the best Rod Seal for your sealing application. Rod Seals act as a dynamic seal along its inner diameter and static along its outer diameter. Rod Seals are affected by changes to the rod surface and fluid temperatures. Rod Seals often see the highest pressure variation. Rod Seals are often the decisive factor in the function of a hydraulic cylinder.
Piston Seals are radial seals. Piston Seals are external seals. Piston Seals fit onto shafts with the sealing lip contacting the housing bore. Piston seals may also be known as Piston Packing. Piston Seals are mounted on a piston head which moves thru the bore of a hydraulic cylinder. Piston Seals can either be single acting or double acting seals. Piston Seals are usually used in conjunction with bearings and guide rings. Piston Seals are typically made of polyurethane but some piston seals can be made of fabric reinforced rubber.
A wiper, also known as a rod wiper, dust seal, excluder or scraper, is a ring in a cylinder that is used to wipe or scrape dirt from the rod or shaft. A wiper helps prevent dirt particles from entering the hydraulic system. A rod wipers main function is to keep the rod and cylinder clean and free from foreign matter preventing premature failure. The wiper is not a pressure sealing element. Wipers most commonly snap into a groove. Some other wipers are made to press into a groove, such as a metal clad wiper. A wiper seal can be made and can function as a wiper and a rod seal all in one groove where space is an issue.
Guide and Wear Rings
Wear Rings are guiding elements that snap onto a shaft, both piston and rod, to keep metal from contacting metal that will damage and score the surface of a cylinder. Wear Rings help keep the cylinder from seizing up. Wear Rings are also know as wear bands, guide rings, wear guide rings, or bearings. Wear Rings have a durable wear rate and non-scoring properties. Wear Rings are made in inch and metric sizes. Wear rings are usually made of fine weave cotton fabric and phenolic resin. Wear Rings absorb transverse loads on the rod and improve the durability of packings in a hydraulic cylinder.
Back-up Rings are used in conjunction with O-Rings for both static and dynamic sealing applications. Back-up rings prevent extrusion of the o-ring when it is subjected to high pressures. Back-up rings help when the extrusion gaps are excessive. Two back-up rings should be used, one on each side of the o-ring, wherever possible. Back-up rings are washer like devices. Back-up rings are not seals themselves. Back-up rings are a support item like a spacer. Back-up rings are available in two designs, a flat washer style and a contoured style. Back-up rings may also be called buffer rings.
O-rings are a one piece object usually molded from elastomeric material. O-rings are in the shape of a torus (donut shape). O-rings can form a static or dynamic seal. A static o-ring seal is used for containing a pressure or maintaining a vacuum. Dynamic o-ring seals can be reciprocating or rotating. An o-ring, when installed, compresses and deforms slightly into the free space within the groove to form a proper seal. O-rings are capable of sealing thousands of PSI pressure. O-rings are one of the most common seals used in machine design. O-rings are one of the most inexpensive seals and easy to make. O-rings are reliable and have simple mounting requirements. And o-ring is measured by its inner and outer diameters. O-rings are described by material composition and hardness. O-rings are typically available in standard sizes per industry standards. O-rings are available in both metric and inch sizes. O-ring selection is based on chemical compatibility, application temperature, sealing pressure, lubrication requirements, quality, quantity and cost. O-rings can also be machined with a CNC lathe.