1. Field of the Invention
The present invention relates to a liquid expulsion apparatus wherein a liquid or liquids are expelled out of a tank by a positive expulsion mechanism. More specifically, it relates to a non-circular liquid expulsion apparatus wherein a non-circular metal diaphragm containing the liquid is attached to a piston, the diaphragm rolling with piston movement preventing the liquid from leaking around the piston.
2. Description of the Prior Art
Liquid expulsion systems in which the liquid is stored in a tank for a long period of time and then rapidly discharged, such as in liquid rocket power plants, generally employ either pistons with rolling metal diaphragms or O-ring type seals, or collapsing metal diaphragms to provide expulsion of the liquid.
Pistons having seals present problems in eliminating leaks across the seal due to high pressure, irregularities in surface contour, and degradation of the elastomeric qualities of the seal. A circular rolling metal diaphragm combining with a circular piston to discharge the liquid was disclosed in U.S. Pat. No. 3,668,868. There, a single cylindrical outer diaphragm was bonded to the inside a cylindrical tank, the end of the diaphragm being attached to the piston head. The piston center support rod passed through a seal which is retained by a metal bulkhead separating two liquid storage chambers. The device is unsatisfactory in that liquid may migrate between the seal and the piston rod, and because of the tank's circular construction does not utilize all available volume inside a container which is non-circular.
A number of patents have issued that disclose collapsible bladders that expel liquids from a tank. For example, in U.S. Pat. No. 4,216,881, I described a geodesic, oblate spheroidally-shaped tank containing a reversible diaphragm, the shape of the diaphragm controlling the collapse mode as gaseous pressure is applied to the "dry" side. Other forms of collapsible diaphragms were disclosed in U.S. Pat. Nos. 3,504,827; 3,722,751; 3,404,813, and 3,339,803. Collapsing metal diaphragms usually present problems due to metal tearing and folding as well as improper collapsing due to uneven pressure points on the surface of the diaphragm.