Which system is designed to hold final control elements in their last known position upon a loss of control air pressure?

The air lock system is designed to hold final control elements in their last known position upon a loss of control air pressure. This is a crucial safety feature that ensures that equipment remains in a specific state during emergencies or failures of the control air supply. The design of the air lock system allows for the retention of pressure in control elements so they don't inadvertently move to an undesired position, which could lead to hazardous conditions or damage to the system.

This system typically employs mechanisms that rely on the existing pressure in the system to maintain the position of control elements, effectively acting as a fail-safe to preserve operational integrity. In environments where systems depend heavily on pressurized air for control and operation, the air lock system safeguards against sudden changes in state that could otherwise result from a loss of pressure.

In contrast, pressure reducing systems are focused on managing and regulating the pressure supplied to a system, emergency shut-off valves are intended to completely stop the flow when certain conditions are met, and water supply systems manage the distribution of water but do not specifically address the situation of maintaining control elements under loss of pressure.