Adjusting the speed of automatic door closers is simple task. Here are a few things that you can do to adjust the speed without having to actually take anything apart.
There typically are two screws on the automatic door that allow for the change in speed. When it comes to the closing speed of the actual door, there is a screw that you can adjust that is labeled with an 'S' which stands for sweep. To make the door close quicker, turn the 'S' screw counter-clockwise and then to make the door close more slowly, you can turn it clockwise.
The 'L' on the screw stands for Latch. To adjust the speed right before the door closes and latches you can change this screw a little bit. Again, to speed it up, counterclockwise and to slow it down, turn it clockwise.
Whether you are changing the speed of the sweep or the latch, you want to make sure that you test it out to make sure that everything is safe. Open and close the door and go through several times to be certain, before allowing others to pass through. If these settings or screws are not available, consult your manual or check online to see how your model differs.