Hydraulic-pneumatic apparatus

A hydraulic-pneumatic apparatus comprising:

• a cylinder assembly including:
• a spindle with a hollow inside;
• a hollow cylinder portion;
• and
• a piston rod capable of reciprocating inside the hollow cylinder portion, and inserted through an inlet of the spindle;
• a flange portion surrounding the piston rod, disposed on an inlet side of the hollow cylinder portion, and contacting an inner circumferential surface of the spindle, wherein:
• a bent portion is formed at the inlet of the spindle to surround and bend the flange portion;
• the flange portion forms a step portion having different diameters along a central axis of the piston rod in a longitudinal direction;
• and
• in one surface of the flange portion, a first groove portion having a preset depth is formed parallel to the central axis of the piston rod along an outer surface of the flange portion;
• a first ring portion formed in a ring shape and disposed in the first groove portion, wherein the first ring portion is formed of a rubber material or a resin material;
• and
• a sealant disposed between an outer circumferential surface of the step portion formed on the flange portion and an end of the bent portion facing the piston rod, wherein:
• the sealant is in a liquid state, a semi-liquid state, or a solid state, and then is cured;
• and
• the sealant is disposed on an inner circumferential surface of the bent portion.