What happens to the heating and cooling valve when a pneumatic thermostat reads 0 psi branch pressure?

When a pneumatic thermostat reads 0 psi branch pressure, it indicates that there is no demand for heating or cooling in the space being controlled. In such a scenario, the system is essentially in a neutral state where the thermostat is not calling for either function.

In typical operation, when the branch pressure drops to 0 psi, it is understood that there is a need to respond to a lack of demand. Therefore, the heating valve opens to allow warm air to flow into the space, while at the same time, the cooling valve closes to prevent cold air from being introduced. This action ensures that the system is ready to provide heating to compensate for any potential drop in temperature without introducing cooling that could make the space colder.

Understanding pneumatic systems is crucial, as they operate based on pressure signals and the interrelationship between different components. In normal functioning, the valves work together to maintain desired conditions within the space. Thus, when the reading is 0 psi, it triggers the system to prioritize heating over cooling, ensuring comfort without overlap in operations.