What is a self-closing door mechanism?
A self-closing door mechanism or door closer is a device which is attached to the top of the door that pulls it shut when the door is released from the open position. This is achieved by means of an arm which rests against the door, which is connected either to a spring or pneumatic piston which pulls the door closed again. The mechanism is typically installed behind the door on the same side as the hinges, although this depends on the style of door closer used and other practical applications such as convenience of installation.
How do self-closing door mechanisms work?
As the door is opened the arm is pulled along, expanding either the spring or the piston. On release, the spring or piston returns to its natural state, pulling the arm and the door along with them, closing the door again and exerting enough pressure to keep it closed.
Where are self-closing door mechanisms used?
These mechanisms are found in many areas of homes but are most typically located on doors leading outside, to help keep out the weather. Most notably, they are a requirement for fire doors; the mechanism assists with keeping flames and smoke inside the building and restricting the supply of oxygen to the fire.
Self closing mechanisms are also used on pool fences to ensure that gates stay closed at all times.
Are there any variations?
Some door closers are connected to a motion sensor, and open and close a door automatically when the sensor is triggered. These kinds of closers are more common in commercial operations where shoppers will frequently have both hands full and may not necessarily be able to operate the door properly.
Another variation involves a chain (similar to a bike chain) attached to the inside edge of the door. The chain passes through a hole in the door jamb, where it's attached to a counter weight hidden inside the wall. As the door is opened, this weight is lifted from its resting position, and when the door is released, gravity pulls the weight back down, closing the door.