This pulley is a wheel around which a cord can pass. Pulleys can be used (typically in combination) to raise heavy weights. The pulley in my demonstration model is used to open a hatch. To close the hatch in my demonstration model I use the forces of gravity. When you release the rope, the hatch will automatically be closed. You can add an iron spring to close the hatch if Newton's laws on gravitation don't work in you favour.The hatch in this model is connected to the wall with a 3Dprinted hinge.