A door closer is a mechanical device that closes a door after someone opens it. Choosing a door closer can involve the consideration of a variety of criteria. In addition to the closer's performance in fire situations, other criteria may include resistance to opening forces
A manual door closer stores the energy used in the opening of the door in a compression or torsion spring and releases it to close the door. Some closers allow for adjustment of the strength of the spring. This makes it easier or more difficult to push the door open.
To limit the speed at which the door closes, most door closers use hydraulic (oil-filled) dampers. The speed at which the door closer closes the door may be adjustable by up to three adjustment valves. These valves often adjust the sweep speed and the latch speed of the door and some closers are optioned with a delayed action valve. The latch speed is the speed that the door travels in the last third to 10 degrees as it closes. It is often set fast so that the door can properly latch closed. The sweep speed is the speed which the door travels at along the first two thirds of its travel. It is often set slower than the latch speed.
For openings where a much longer close time is desired, you may opt for a delayed action closer. The delayed action valve slows the sweep speed dramatically for roughly the first half of the sweep range. Door closers which provide this two or three-stage action and close doors at a determined rate are called 'controlled' door closers.
An automatic door closer (more often called a "door opener") opens the door itself, typically under the control of a push button, motion detector or other device. It also has a motion or proximity detector to determine when it is safe to close the door.