How do automatic door closers work?


Quick Answer

Automatic door closers work by storing energy in a tension spring when a person opens a door and then releasing that energy when the person walks away. Most automatic door closers also use a piston of some kind to prevent the spring from slamming the door shut and potentially causing damage. Automatic door closers are distinct from automatic door openers, which use electrically powered hydraulic cylinders to open and close doors.

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Full Answer

When someone walks through a door equipped with an automatic door closer, an arm attached to the mechanism compresses a spring inside the device. As soon as the person stops holding the door open, all the energy in the spring gets released, and the arm forces the door shut. Because springs release their energy all at once, door closers use some kind of arresting mechanism to release the spring's energy gradually.

Most light doors, such as storm doors or screen doors, use an automatic door closer with an air piston. When the compressed spring releases its energy, it presses up against the air piston. As the piston contracts, it releases air, producing the characteristic hissing sound associated with these door closers. Automatic door closers can also use small, unpowered hydraulic pistons to absorb the spring's energy. Door closers with hydraulic pistons are more expensive than those with air pistons, but they are more powerful, reliable and produce almost no noise.

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