Systems and methods for providing a variable pumping stroke from a pump comprising a pumping chamber, a pump inlet, a pump outlet, a valving mechanism, and a drive piston. In one embodiment, the pump inlet is in fluid communication with the pumping chamber regardless of the location of the drive piston within the pumping chamber, and the pump outlet is similarly in fluid communication with the pumping chamber regardless of the location of the drive piston within the pumping chamber.