Self-Operated, No External Power Source The Mark 80 Series is completely self-operated and requires no external power source or other expensive instrumentation to operate the valve. Depending on valve action, the seats open or close as bulb senses rise in temperature. The Mark 80 has high rangeability - controls flows from 10% to 90% of rated capacity. Available with up to 100 feet (30 meters) in capillaries.