The small air cylinders welded to the sides of the main hydraulic cylinders act like air springs. Because the static weight of the lifting frames is minimal, the air cylinders assist lowering the frames after the vehicle's tires touch the floor, or if the lift was ever raised with no load.
An alternative method, but not quite as appealing would be to attach large springs to the jack frames similar to those used on BendPak’s P-6 low-rise lift as shown here; tolerable on the P-6, but probably not the best option for the lightweight QuickJack.
Inflate each air bottle cylinder to 50-PSI. Be sure to pull the connector off quickly to minimize air loss and don’t forget to replace the dust caps as they help to retain air. The cylinders will require periodic recharging.