Equal area displacement hydraulic cylinder

Claim 1

In an equal area displacement hydraulic cylinder having an outer tube; blind end and rod end caps receiving and secured to opposite ends of said tube; and a gland in said rod end cap; a hollow piston rod within said tube along its length projecting through said gland, and defining with said tube a first chamber; a rod end secured within the outer end of said piston rod adapted for connection to a device for effecting reciprocal movements thereof; a reciprocal piston in said first chamber secured to said piston rod; a stationary open-ended inner tube within said piston rod along its length and at one end anchored to said blind end cap and extending therethrough, terminating in a first port; said port communicating with a second chamber in said inner tube; said stationary tube being spaced from the wall of said piston rod, defining a third chamber; a stationary piston upon the other end of said stationary tube engageable with the bore of the piston rod and said closing off third chamber; said second chamber communicating with a fourth chamber upon the far side of said stationary piston, closed by said rod end; there being a second port in said rod end cap communicating with said first chamber; whereby on pressurizing said second port, said movable piston and piston rod are retracted; alternately pressurizing said first port and second chamber, advancing said piston rod with respect to the stationary piston; the effective working area of the piston in the first chamber being equal to the effective working area of the rod end closing the fourth chamber, whereby equal rod force is delivered to said reciprocal piston rod in both directions; forward movement of the reciprocal piston and piston rod within said first chamber causing relative movement of said piston rod with respect to the stationary piston, said third chamber being vented through said blind end cap; a retainer assembly including an apertured retainer plate secured upon said rod end cap receiving said gland and rod end; a pair of spaced apertured anchor plates secured to and projecting forwardly of said retainer plate; and the volumetric capacity of the first and fourth chambers when extended being equal.