The principle of vacuum furnace design involves evacuating the ambient air from the furnace during heat treatment initiation while simultaneously introducing process gases to achieve a specific sub-atmospheric pressure. Consequently, vacuum furnaces enable precise control over the quantity, type, and quality of gases within the furnace throughout the entire process. Inert gas quenching is a widely employed technique to regulate quenching rates and outcomes. Additionally, as temperatures rise in the heat zone, introducing specific process gases can yield further benefits, thereby improving results in various heat treatment applications. 

The first step in vacuum heat treatment is removing air from the furnace. Heated metal components are particularly prone to reacting with common elements in air (such as water vapor or oxygen), so air removal significantly reduces unwanted harmful reactions. However, introducing specific process gases can also generate reactions or conditions necessary as part of the process. Replenishing process gases during heating offers numerous advantages.

 Some processes may require introducing minimal amounts of gas (0.01 Torr to 10 Torr), such as hydrogen to aid in oxide removal or adding elements like carbon for surface carburization hardening, or other inert gases to limit the volatilization of elements like chromium during high-temperature processes. Other processes may necessitate introducing sufficient process gases (1 atm or higher) to enable convective heating through internal fan operation, ensuring uniform heating of parts with complex geometries or large cross-sections. The furnace design includes two differential pressure gas inlets, regulated by mass flow meters. 

Here, we observe a typical differential pressure system comprising mass flow meters, pressure regulators, shut-off valves, and differential pressure manual throttle valves, which enable precise control over the volume of gas introduced into the furnace.