Abstract: A cylinder structure and method for rapidly evacuating a cylinder without contamination thereof. The structure comprises a hollow cylinder, a piston mounted in the cylinder for axial reciprocation, a hollow piston rod secured to the piston for movement therewith extending out of one end of the cylinder, a seal between the one end of the cylinder and the piston rod, and a radial opening through the hollow piston rod between the piston and seal for evacuating the space between the cylinder, piston, piston rod and seal during reciprocation of the piston within the cylinder. The method includes the step of evacuating the space between the cylinder, piston, piston rod and seal through the piston rod during reciprocation of the piston within the cylinder.