| 摘要 |
An elongate cylindric tank for transport or for storage in bulk of semisolid and fluid materials, such as grease and oil with an outlet at one end thereof and a generally cylindric piston sized to slide therein and be moved in a direction toward the outlet, thereby forcing the material in the tank through the outlet. The piston includes a piston member, with a circumferential channel adjacent one end thereof, a seal for sealing the piston member against the interior surface of the tank, and a mechanism for holding the piston against canting in the tank while permitting the piston to slide freely in the tank. The seal comprises an elastic annular packing disposed at least partly within and carried by the channel and a circumferential flexible sheath overlying the packing and protecting it. The packing is hollow and expandable by varying the pressure within the packing between atmospheric pressure and a higher pressure wherein the packing expands and presses the sheath in sliding engagement against the internal tank surface thereby to wipe the material therefrom and to seal the piston member relative to the tank. The sheath prevents the material contained in the tank from contacting the packing.
|
