A hinge pin door closer can be a great solution for getting a door to close when you don't really have the room to mount a traditional hydraulic door closing unit. These units can be a little more expensive than traditional models, but actually require less work to install in comparison.
Hydraulic Pressure and Gravity Models
A hinge pin door closer works the same as any other hydraulic door closure through the use of reverse air pressure. What happens is that when the door is opened, you are manually pulling the lever or control arm on the unit out. This is removing air from the chamber on the inside of the unit, creating a tight vacuum.
The Power of a Vacuum
A hinge pin door closer works on the physic laws of vacuumed space. When a vacuum is created, it is pulling pressure in from all sides, trying to fill its own empty space, thus relieving pressure.
Spring Loaded Soft Closing Systems
Some hinge pin door closer units do not use a hydraulic system to retract the door. The instead have a very strong springing system, that when the door is opened, stretches the spring. When you let go of the door, the spring recoils back to its normal or rested state, causing it to release the generated energy, and pull the door shut.