From a vacuum technology point of view the seal side of the valve is the vacuum side (toward the pump). This allows for atmosphere to help keep the valve closed if the bellows side of the valve is at atmosphere. From a process point of view the bellows side is the vacuum side. This minimizes the amount of surface area in the valve that is exposed to the process. Most valves can be installed either way, but as they get bigger, only the seal side toward the pump will provide a reliable seal.
Category: Vacuum Valves
Sub-Category: Gate Valves