packing stack, is flat on one side and V-shapedon the other to properly support the adjacentV-ring. Proper design and installation of thefemale adapter has significant impact on theservice life and performance of the V-ringsbecause the female adapter bridges the clearancegap between the moving surfaces and resistsextrusion.The packing set is installed in a cavity that isslightly deeper than the free stack height (thenominal overall height of a V-ring packing set,including the male and female adapters asmeasured before installation) and as wide as thenominal cross section of the V-rings. This cavity,called a packing gland or stuffing box, containsand supports the packing around the shaft, rod,or piston. Adjustment of the packing gland depththrough the use of shims or spacers is usuallynecessary to obtain the correct squeeze orclearance on the packing stack for good servicelife.Two basic installations apply to V-ringpackings. The more common is referred to as anoutside packed installation, in which the packingseals against a shaft or rod, as shown in figure7-4. The inside packed installation, is shown asa piston seal in figure 7-5. When V-ring packingis to be used in an inside packed installation, onlyendless ring packing should be used. Wherepressures exist in both directions, as on adouble-acting piston, opposing sets of packingFigure 7-5.—Inside packed V-ring installation.should always be installed so the sealing lips faceaway from each other as in figure 7-5. Thisprevents trapping pressure between the sets ofpackings. The female adapters in inside packedinstallations should always be located adjacent toa fixed or rigid part of the piston.O-RINGSAn O-ring is doughnut-shaped. O-rings areusually molded from rubber compounds; how-ever, they can be molded or machined from plasticmaterials. The O-ring is usually fitted into arectangular groove (usually called a gland)machined into the mechanism to be sealed. AnO-ring seal consists of an O-ring mountedin the gland so that the O-ring’s cross sectionis compressed (squeezed) when the gland isassembled (fig. 7-6).An O-ring sealing system is often one of thefirst sealing systems considered when a fluidclosure is designed because of the followingadvantages of such a system:1.2.3.4.5.6.7.SimplicityRuggednessLow costEase of installationEase of maintenanceNo adjustment requiredNo critical torque in clampingFigure 7-6.—O-ring installed in a gland.7-6
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