LF5D series differential pressure control / switch is normally use in water, oil series control difference of the outlet tube and inlet tube. One typical application is , put valve install  in the next to water (oil) system pump's by-pass valve line ,when the pressure difference rise (or reduce) of two side of the system's tube exceed the setting data of the pressure control, so the valve open big (or close small), so  the system tube's two side's pressure difference is reduce, to reach the system normal circulate.
LF5D series differential pressure control's two side have a high-sensitive parts each other, when the pressure of  two side of the parts change, it will let switch institution action to control system's equipment, such as motor drive's valve.