check the following site. they have valves listed for the YORK furnace. As you'll see some systems are millivolt, some are 24 volt control. a thermocouple looks like a 1'8th inch copper tubing terminating with a screw on gland and a silver button on one end and a 5/16" tube with two jam nuts on it. this end goes into the flame to detect and generate a millivolt signal from about 250 to 750 millivolts.
Gas Valves - Trane: American HVAC Parts