| 摘要 |
An elongate tank for transport or for storage in bulk of semisolid and fluid materials, such as grease and oil. The tank has an outlet at one end thereof for discharging material contained therein, and has a generally cylindric interior surface. A generally cylindric piston is sized to slide in the tank and is movable in a direction toward the outlet thereby to place material in the tank through the outlet. The piston comprises a piston member and an elastic annular seal carried in a circumferential channel around the piston member. The seal has an annular base and an annular crown disposed radially outwardly of and joined to the base with a fluid chamber between the base and crown. The seal is expandable by introducing fluid into the fluid chamber. Expansion of the seal causes the crown to be pressed radially outwardly against the interior surface of the tank so that when the piston member slides in the tank a portion of the crown is maintained in sliding engagement with the interior surface thereby to wipe the material therefrom and to seal the piston member relative to the tank. The crown has side surfaces and an outwardly facing surface. The outwardly facing surface of the crown has two sloping surface portions and a circumferential ridge intermediate the side surfaces. The ridge is defined by the junction of the surface portions.
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