These are 2 step servo controlled main valves with screwed-on pilot solenoid valves. These valves use an external pressure source for opening (which means that no differential pressure across the valve is required). These are used in suction lines for opening against high differential pressure e.g. after hot gas defrost in large industrial refrigeration systems with ammonia or fluorinated refrigerants.
These valves open in two steps.
Step one opens to approx 10% of the capacity, when the pilot solenoid valve are activated.
Step two opens automatically after the pressure differential across the valve reaches approx 1.5 bar.