INTRODUCTION
MTSV valves are servo-operated main valves with screwed-on pilot solenoid valves are 2-step servo-controlled main valves with screwed-on pilot solenoid valves. Both types use an external pressure source for opening (which means that no differential pressure across the MTSV valve is required). MTSV are used in suction lines for the opening against high differential pressure, e.g. after hot gas defrost in large industrial refrigeration systems with ammonia or fluorinated refrigerants.