T-seals are used in applications where largeclearances could occur as a result of the expansionof the thin-walled hydraulic cylinder. The T-ringis installed under radial compression and providesa positive seal at zero or low pressure. Backuprings, one on each side, ride free of T-ring flangesand the rod or cylinder wall (fig. 7-2, view B).These clearances keep seal friction to a minimumat low pressure. When pressure is applied (fig. 7-2,view C), the T-ring acts to provide positive sealingaction as fluid pressure increases. One frequentlyused T-ring, manufactured by Greene, Tweed andCompany, (called a G-Tring®1), incorporates aunique, patented backup ring feature. One corneron the ID of each radius-styled backup ring onthe G-Tring® set has been rounded to mate withthe inside corner of the rubber T. Figure 7-2, viewsB and C, shows the G-Tring®.There is no military standard part numberingsystem by which T-seals can be identified. Ingeneral, each manufacturer issues proprietary partnumbers to identify seals. However, it is commonpractice to identify T-seal sizes by the samedash numbers used for equivalent O-ring sizes(discussed later in this chapter) as defined byAS568 and MS28775 dimension standards.Typically, an O-ring groove that accepts a certainO-ring dash number will accept the same dashnumber T-seal.In the absence of an existing military standardfor identifying T-seals, a new and simple1G-Tring® is a Greene, Tweed Trademark,numbering system was created to identify T-sealsrequired for hydraulic actuators (piston seals only)without reference to a particular manufacturer’spart number. The Navy number is composed ofthe letters G-T followed by a dash number of threedigits and one letter, R, S, or T (for example,G-T-217T). The three digits are the appropriateO-ring size dash number according to AS568 orMS28775. The letters R, S, and T designate thenumber of backup rings that the groove of theT-seal is designed to accommodate: none, one,or two, respectively.V-RINGSThe V-ring is one of the most frequently useddynamic seals in ship service although itsidentification, installation, and performance areprobably most misunderstood. Properly selectedand installed, V-rings can provide excellent servicelife; otherwise, problems associated with friction,rod and seal wear, noise, and leakage can beexpected.The V-ring is the part of the packing set thatdoes the sealing. It has a cross section resemblingthe letter V, (fig. 7-3) from which its name isderived. To achieve a seal, the V-ring must beinstalled as part of a packing set or stack, whichincludes one male adapter, one female adapter,and several V-rings (fig. 7-4). The male adapteris the first ring on the pressure end of the packingstack and is flat on one side and wedge-shapedon the other to contain the V of the adjacentV-ring. The female adapter, the last ring of theFigure 7-4.—Outside packed V-ring installations.7-5
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