How many control valves are required for the most basic gas defrost to function properly?

In a basic gas defrost system, only one control valve is typically required for it to function properly. This control valve is essential for regulating the flow of refrigerant gas during the defrost cycle. The system needs to efficiently manage the distribution of gas to the evaporator to facilitate effective heat transfer, thus enabling the melting of ice build-up on coils or surfaces.

Having just one control valve simplifies the operation, allowing for straightforward control over the refrigerant flow and ensuring that the defrost process can be initiated and terminated as needed. In more complex systems, additional control mechanisms may be used, but for the most fundamental application of gas defrost, one control valve suffices to operate the system effectively.