Commercial Door Closers
Door closers are required on fire rated doors so the door will close after somebody has passed through it. The door can then retard the fire as it was meant to. Closers are also used on many non fire rated doors. Anywhere you want to assure the door closes behind you, a door closer will do the job.
Almost all closers will have a sweep and latch speed adjustment. The sweep is the movement of the door from the open position to just before it latches into the frame. The latch is those last few inches just before the door actually reaches the latch. You can adjust the speed of either one of these to obtain the results you require. Sometimes you will need the door to close quickly (not on handicapped doors) and then slow down right before closing to avoid slamming. Other times you will need the door to close slowly and then speed up at the very end to be sure it actually latches.
The backcheck control will let the door open at the normal speed to almost 90 degrees and then slow the door down for the rest of the opening cycle so the door doesn't swing open out of control allowing someone in a wheelchair, for example, to have time to get through the opening.
Some closers are available with the hold open arm feature. This closer will let the door automatically stay open when it is opened to a certain point. You only need to pull the door a little to make it close normally. If the door is opened to less than the hold open point, it will close as if it did not have a hold open arm. The hold open arm can not be used on a fire rated opening.
Delayed action closers will hold the door open for a period of time before it starts to close.
The two most popular ways to mount the door closer are either standard (regular) arm or parallel (pa) arm. The standard arm closer always mounts on the pull side of the door, so it would never be used on exterior outswing doors. It has a better power efficiency than the PA arm, but the arm projects out from the door. The parallel arm closer always mounts on the push side of the door. While it is not quite as strong as the standard arm mount, it is still plenty strong enough for most applications and it looks better as the arm lays parallel with the door in the closed position.
There are many variations on this such as top jamb mount, concealed closers, floor closers, etc., but these two are used the most.