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Mechanical devices known as seals, packings, and Sacramento gaskets are used to prevent leakage of fluids, gases from cylinders and cylinder-head in engines, hydraulic pressure cylinder and cover head. These devices also prevent the penetration of foreign matter into the concealed system. Seals are available in various forms and design configurations and the selection of a seal depends on: (a) pressure, (b) temperature. (c) Medium, that is, liquid, solids, gases, (d) corrosive atmosphere, and (e) shaft speed, etc. Seals can be broadly classified as static and dynamic seals. The static seals are further classified into the following categories: Gasket is a thin layer of soft material in between two surfaces to be sealed, such as a cylinder head and cylinder in engine block, cover-head flange and cylinder flange in high pressure vessels. Direct contact seals are the two surfaces are directly making metal to metal contact under high squeezing pressure, where very high pressures are involved. Sealants- Instead of being preformed, some gaskets are formed in place. Squeezing a bead of plastic gasket material or sealant from a tube into one of the mating surfaces, such as valve covers, thermostat housings, water pumps, differential covers. Dynamic seals are used on rotating or reciprocating shafts. On rotating shafts, there are two types of dynamic seals used: (1) interfacial, when the seal touches the shaft and (2) interstitial, where clearance between shaft and seal exists in radial or axial direction or in both radial and axial directions. On reciprocating parts such as pistons, there are three types of seals used: (1) packing, (2) diaphragm and (3) rings. Gasket A gasket is a thin layer of soft material such as paper, cork, copper, synthetic material, or a combination of these. Sacramento gaskets can be preformed or precut to the desired shape (simple or complicated depending upon application). Clamping the gasket between the two flat surfaces makes a tight seal. The clamping force resulting from the tightening of the fasteners squeezes the gasket. Soft material of gasket deforms and fills the irregularities in the mating surfaces. This prevents the leakage of the fluid, vacuum, or pressure from the joint. Holes through the gasket allow it to seal in fuel, oil or coolant. The gasket material keeps dirt, dust, water or air out of the package. Sometimes, the gasket serves as a shim to take up space. An automobile uses variety of gaskets, especially in the engines. The head gasket seals the cylinder head and cylinder block. Gaskets can be classified as: (1) metallic, (2) non-metallic, and (3) a combination of metallic and non- metallic. Moreover, these gaskets are either self-energized gaskets or non-energized gaskets. Metallic gasket seals that do not take advantage of internal pressure to improve the sealing effect are non-energized type. The various gasket configurations are: (1) flat, (2) round section, (3) heavy section, (4) corrugated shape, (5) spirotallic shape, or (6) metal jacketed shape. The Author is a professional writer, presently writing for rubber products, and to get more detail please visit here http://www.sacramentorubberproducts.com
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