The days of the slamming screen door are just about gone -- the old-fashioned spring has been replaced by the pneumatic closer. Instead of slamming the door with a crash, it slowly draws it shut, almost without a whisper.
At least that's the way it's supposed to work. But it may fail to close the door securely so a strong gust of wind can whip the door open and rip if off its hinges; or it may work too fast, producing the slam it was designed to eliminate.
Both these problems are easy to cure. At the end of the closer is an adjustable screw. If your door closes too quickly, turn that screw clock-wise a turn or two. Test the door; if it still closes too quickly, turn the screw some more. Keep at it until you're satisfied.
Door closes too slowly? Turn the screw counterclockwise, again testing until you get the closing speed you want. You should aim for a speed that lets you slip through the door with an arm full of packages without getting slammed from behind -- but without too much room to spare.
That adjusting screw will take care of closing speed, but even if your door closes at the right speed it may not latch properly. In this case you want to adjust closing power. Closing power is not the same as speed. To adjust closing power you move the door bracket -- that piece of hardware securing the closer to the door.
If you want to increase closing power, loosen the screws holding the bracket in place and slide it a notch or two toward the closer. Retighten the screws and check the results. If the door has too much closing power and shuts with a bang, slide the bracket away from the closer.
Sometimes latching problems are not caused by the closer but by the door. Screen and storm doors often sag after a few years of use, so they don't fit their openings properly and rub against the jamb or sill. Friction then keeps them from closing no matter how you adjust the closer.
The solution is a storm-door brace, two metal rods joined end-to-end by a turnbuckle. You screw it to your door at an angle, running from the bottom of the latch edge up toward the top of the hinged edge. Once the brace is in place, use a wrench to tighten the turnbuckle. Turn it a revolution or two and check the door's fit. Keep tightening until the sag is pulled out of the door and it swings freely.