Fluid compression system

A fluid pump comprising a chamber containing a fluid, the chamber having a fluid inlet and a fluid outlet, a compression member having a compression surface with an effective surface area movable against fluid pressure in the chamber, the compression member having a compression stroke and a return stroke, the effective surface area of the compression member decreasing in size together with a corresponding cross-sectional area of the chamber from a maximal area at a beginning of the compression stroke to a minimal area at the end of the compression stroke, compression member having a piston mounted for linear reciprocable movement in the chamber, the piston comprising at least first and second concentric piston portions which are releasably interconnected to one another;

• when the at least first and second concentric piston portions are interconnected for joint movement, the effective surface area of the piston being equal to the combined surface areas of the first and second concentric piston portions;
• when the second piston portions is released from the first piston portion, thereby allowing the first piston portion to continue its stroke, the effective surface area of the piston being equal to the surface area of the first piston portion alone, wherein a releasable connector is provided between said at least first and second concentric piston portions, said releasable connector comprising a biasing member mounted to one of said first and second concentric piston portions and urging a locking member in engagement with both the first and second concentric piston portions, wherein said locking member comprises a locking ball trapped in opposed facing depressions defined in adjacent surfaces of the first and second piston portions, and wherein the second piston portion is engageable in an axially abutting relationship at one point during the compression stroke with an inner shoulder provided on an inner wall of the chamber, the engagement of the second piston portion with the inner shoulder preventing further axial advancement of the second piston portion in the chamber, and wherein a shear force resulting from the continued advancement of the first piston portion after the second piston portion has axially abutted against the inner shoulder causes a biasing force of the biasing member to be overcome, thereby allowing the locking ball to move further into one of said opposed facing depressions and out of engagement from the other one of the depressions to effect disconnection of said first and second piston portions.