Heat treating apparatus and method of operating heat treating apparatus

A heat treating apparatus comprising:

• a core tube for containing a material to be treated, the core tube being supplied with gas from a core tube gas supply means;
• a heating furnace surrounding the core tube, the heating furnace being supplied with gas from a gas supply means and the heating furnace being sealed with respect to the core tube;
• differential pressure detecting means for detecting the differential pressure between the pressure in the core tube and the pressure in the heating furnace;
• and
• differential pressure regulating means for regulating the differential pressure between the gas pressure in the core tube and the gas pressure in the heating furnace in response to a differential pressure signal received from the differential pressure detecting means, the differential pressure regulating means comprising an exhaust conduit communicating at one end with the core tube and communicating at another end with a means for exhausting the core tube gas through the exhaust conduit to the atmosphere and an adjusting means operatively connected with the exhaust conduit for adjustably feeding external air into the conduit in response to the differential pressure signal.