Seals prevent or reduce fluid passage between 2 surfaces. Imperfect mating parts require some type of sealing devices to be inserted between them to seal against loss of liquid, gas or solid fluids or particles.
Sealing Devices offers many types of seals from o-rings that seal water, aircraft fuels and many media on pumps, electronic devices, compressors, transportation vehicles, food processing equipment and medical devices to complex EMI shielding gaskets that block electromagnetic interference in electronic enclosures and devices. Sealing Devices also provides molded rubber seals, extrusions, lathe-cuts, gaskets, packing, Teflon seals, mechanical seals, graphite, cloth, metal seals, o-rings and metal rings, and a complete line of oil seals. Some of the most common types of seals Sealing Devices provides include:
Aerospace seals and aircraft hydraulic components and systems require custom seal engineering to achieve minimal leakage and maximum performance to insure long seal life, and optimize safety concerns. Aerospace seals expertise include an in-depth understanding of elastomers and composites. Sealing Devices has experience with custom aerospace seals, and offers many items including geltek silicone sealant strips from stock.
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The main tasks of hydraulic seals are to retain hydraulic fluids, exclude solid or liquid contaminants and to maintain hydraulic pressure. These tasks require different seal designs and accessories. Key types of hydraulic seals include:
- Piston Seals
- Rod Seals
- Wiper Seals
- Guide Rings
Metal-Jacketed gaskets are suited for smooth surface applications such as heat exchangers, vacuum lines, cast iron flanges, autoclaves, boilers and glass-lined equipment. Applications often require a minimum of 20 to 30 percent compression to compensate for flange misalignment, warping, etc. Metal gaskets are designed for use in assemblies where the elasticity of bolts or flange design can compensate for joint relaxation. They are fabricated with a soft filler, partially or wholly encased in a metal jacket, and the primary sealing interface is the inner metal lap where the gasket is thickest when under compression. This area flows into the flange surfaces to create the joint seal; therefore, the entire inner lap must be under compression. The outer lap, if any, when under compression between the flange faces provides a secondary sealing line.
The purpose of piston seals in hydraulic cylinders is to maintain a high level of sealing performance throughout service life. For a cylinder which is exclusively single-acting, choose the type of seal designed to provide optimum sealing for single-acting functions with the thinnest lubrication film that can pass through the contact area between the seal and the cylinder surface. The best sealing for a double-acting cylinder can be achieved by choosing a double-acting seal. Piston seals, both single- and double-acting, can be designed for and used with integrated or separate back-up rings and guide rings. The ultimate choice must be based on the operating conditions of the cylinder.
- Pneumatic Seals
- Piston Seals
- Rod Seals
- Wiper Seals
- Guide Rings
Quad Rings (Square Rings or X-rings)
Quad rings can be used both static and dynamic sealing applications. The four-lobed design provides twice the sealing of a standard O-ring, but requires less squeeze to maintain an effective seal. This reduction in squeeze means less friction and improved seal life, and because parting lines are between the lobes, away from the sealing surface, problems of leakage associated with o-rings is virtually eliminated. Also, quad ring construction creates a more stable seal avoiding spiral twisting.
Radial Shaft Seals
Radial shaft seals are used between rotating and non-rotating machine components, and are made of:
- a cylindrical outer covering of sheet steel shell or elastomer which seals statically against the housing bore and enables an interference fit of the seal in the housing bore to be obtained and facilitating proper installation.
- an elastomer which provides dynamic and static sealing against the shaft. A sealing lip has an edge which is formed by pressing, cutting or grinding and is normally pressed against the counterface on the shaft with a defined radial force by a spring. The edge of the sealing lip and the shaft counterface form the most important functional area of a radial shaft seal. Another sealing lip can be provided to protect the sealing contact proper from dust and other fine solid contaminants. A lubricant in the space between the sealing lip proper (primary lip) and additional (secondary) lip can reduce wear and delay corrosion.
The most demanding seal in the hydraulic cylinder is the rod seal. In addition to normal wear and aging, rod seals are affected by changes on the rod surface. The rod seal is often the decisive factor for the function of the hydraulic cylinder in its entirety. Leakage through the rod seal can in some cases cause accidents and environmental damages.
Parker's Standard PolyPak® (SPP) is a square cross-section squeeze seal with a symmetrical profile for use in either rod or piston applications. The standard Molythane shell provides high wear resistance and the O-ring energizer functions as a spring to maintain sealing contact under low pressure. The standard PolyPak utilizes a scraper lip design formed by a precision trimming process. The scraper edge wipes both fluid film and contamination away from the seal. A wide selection of sizes and alternate compounds allow this profile to match up with many hydraulic applications.
Urethane O-ring Seals
O-rings seal through deformation between two surfaces against which it is supposed to seal. The working pressure at which the O-ring can be used is dependent on among the installation mode, fitting clearance, the elastomeric material, sealed medium and temperature. O-rings are one of the most common sealing devices used in sealing applications.Wiper Seals
Contamination particles in the hydraulic system are a primary reason for the failure or short service life of seals. Most particles reach the system through the rod. A wiper seal can be installed to prevent seal failure and system breakdown.
The choice of wiper seal should be made based on the choice of piston and rod seals. The surrounding environment and service conditions need to be taken into consideration when choosing wipers. The wiper seal needs to fit both the rod (dynamic) and also to the housing (static).
Sealing Devices offers a complete line of Parker o-rings, polypaks, hydraulic seals, and sealing materials from stock, and is a Certified Parker Sealing Technology Center.