Apparatus for automatically closing a swing door

An apparatus for automatically closing a swing door, comprising:

• a cylindrical body designed for installation in the door;
• and a base plate to be fixed to a wall;
• the cylindrical body comprising:
• a first cylinder that serves substantially as an outer casing for accommodation of other members constituting the apparatus and defined below;
• a second cylinder disposed in the first cylinder and capable of sliding a given stroke within and longitudinally of the latter;
• a third oil hydraulic cylinder accommodated in the second cylinder and having an end secured to a piston-like part formed at a rear end of the second cylinder;
• a piston rod held to be displaceable into and out of the third cylinder, having a rear end fixed to a piston in the third cylinder, and having a front end connected by a connecting pin to the first cylinder;
• a tie rod connecting a front end of the second cylinder to the base plate;
• a substantially airtight chamber defined between the piston-like part of second cylinder and an inner surface of a rear end wall of the first cylinder;
• an air suction passage through which the chamber communicates with atmosphere;
• a one-way valve disposed in the air suction passage so as to allow only suction of air into the chamber;
• and
• a thin ventilation hole communicating with the airtight chamber, so that the air compressed therein is discharged slowly to the atmosphere, wherein the third cylinder is such that the piston rod is urged towards a home position thereof when freed after pressed deep into the third cylinder.