Here are a few of the door closer adjustments that most door closers have:

Door Closer Adjustments
Tighten (clockwise) the valve to decrease the speed
Closing Speed Valve- The valve that controls the speed of closing from about 75 to 15 degrees,
some times marked “C”
Latching Speed Valve – The valve that controls the speed of the last 15 degrees,
some times marked “L”
Back Check Valve – The valve that controls the amount of resistance the closer has if it is
thrown open or if wind catches it.
Power Adjustment – This valve controls the spring tension, which will make the door closer open
harder or easier depending on were you adjust it.  Only a few models have this option.

If your door closer is slamming it means the hydraulic fluid has leaked out, and with out the fluid there is nothing to retard the motion.  Use the Door Closer Guide on this webpage to figure out which closer you should replace it with on our website.