Final answer:
The movement of a cylinder in a hydraulic or pneumatic system when pressure is applied depends on the system's control mechanisms and safety features. It will generally move in the direction indicated by the engaged manual switch, unless overridden by other factors.
Step-by-step explanation:
The question relates to the behavior of a hydraulic or pneumatic system when pressure is applied or released. In pneumatic systems, the inconsistent compressibility of gases can affect the performance of the system. According to the given scenario, if a manual switch is pressed and held, and then the pressure supply is turned on, it would depend on the configuration of the valves and the system whether the cylinder would extend or retract. However, generally, upon the introduction of pressure, the cylinder is likely to move in the direction the control system is designed for when the manual switch is engaged, unless there is an override or safety mechanism.
The principles of gas pressure and hydraulic systems outlined in the provided information demonstrate that the performance of a cylinder in a pneumatic system can vary depending on whether the gas is being compressed or expanded. As indicated in the provided excerpts, when the volume of a gas is reduced within a container with a fixed volume, the pressure increases. This principle suggests that if the pneumatic system's cylinder is in a neutral position and pressure is applied, it will extend or retract based on the direction that pressure forces it, assuming there are no other variables at play like control valve positions.