This is the ball pump. Plastic balls drop into the pump from the vertical column on the top of the pump. A piston inside the pump retracts toward the lower left allowing a ball to drop into the drive chamber. The piston is then actuated toward the upper right, thereby pushing the ball through the drive chamber. There are spring loaded catches mounted inside the drive chamber just beyond the furthest extent of the piston's travel. The balls push catches open in the positive drive direction. Once the piston has pushed the ball clear of the catches, the springs return the catches to prevent the balls from descending back into the drive chamber.