Air Cylinder

An air cylinder comprises:

• a piston, an inner tube, an outer tube, a cylinder tank, a control valve, an O-ring, a bearing, and an oil seal,
• the inner tube inserted in the outer tube,
• the outer tube inserted through the cylinder tank,
• the control valve disposed on a top end of the inner tube,
• the bearing disposed on a bottom of the inner tube,
• the O-ring enclosing the bearing,
• a first sealing device having an annular shape being disposed between an inner wall of the outer tube and the control valve to separate the O-ring and the outer tube so as to form a uniform and smooth first inner face on the inner wall of the outer tube, and
• a second sealing device having an annular shape being disposed between the outer tube and the oil seal so as to form a uniform and smooth second inner face on the inner wall of the outer tube.