Damper for a pivot door

A damper for a pivot door, the damper comprising:

• a housing having a space full of hydraulic oil, an annular protrusion defining therein a first channel and a second channel, a path defined through the protrusion, a positioning seat integrally formed at a mediate position of the housing, a guide board movably mounted inside the housing and having a pair of spaced first rollers rotatably mounted on the guide board, a T shaped mount securely mounted onto the guide board and having a second roller rotatably mounted onto the mount;
• wherein the first and second channels selectively communicate with the space;
• a cam rotatably mounted onto the guide board and engaging with the first rollers and the second roller;
• a drive shaft securely mounted onto the cam and a free end of the drive shaft being adapted to pivotally connect with the door;
• a piston having a first chamber, a second chamber in the piston, a groove annularly defined in a periphery of the piston and a piston rod securely connecting the piston to the guide board,
• wherein the first chamber is divided into a large room for movably receiving therein a spring and first ball combination and a small room selectively communicating with the large room for receiving therein a grill and a perforated lock and the small room has a diameter smaller than that of the large room,
• wherein the second chamber is divided into a first room for movably receiving therein a second ball and a second room selectively communicating with the first room and having a diameter smaller than that of the first room;
• a recoil spring mounted around the piston rod and one end of the recoil spring abutted an underface of the piston and the other end of the recoil spring being received in a notch in the positioning seat,
• whereby when the piston moves, the recoil spring is reciprocally compressed and released and hydraulic oil flowing to the path from the space via the first and second chambers facilitates the movement of the piston,
• when the hydraulic oil flows to the space from the path by way of the second channel, a damping effect is created so as to function as a damper to protect the door.