Ace Furnace Consulting Ltd


Ace Furnace

Controlling Leakage Across a High Temperature Seal using Differential Pressure

In this application a HORNER APG XL6 combined touch screen and PLC unit drives a pair of fans extracting gas from large vessels within a vertical chamber furnace.


The vessels are heated to above 500°C during the process, and a connection is needed in the base of the furnace that allows a vessel to be engaged and disengaged from the gas extraction pipe.


A multi-element seal with flexible rings of glass cloth stuffed with ceramic fibre is fitted to a fixed spigot in the base of the furnace. Each vessel is fitted with a matching socket.


The seal is robust and stands the temperature together with repeated engagement  and disengagement, but the environment means a fully tight seal cannot conveniently be engineered.


Seal performance is therefore enhanced by active control of the differential pressure across it.


The 2 m high vessel hangs from the top and expands downwards more than 20mm during the heating cycle.

Pot connection 1

Differential pressure between the inside of the vessel and the furnace in which it is suspended is continuously monitored and a fan connected to the gas extraction pipe is speed controlled to maintain a small differential pressure of around 5 pascals across the seal. This prevents leakage outward, replacing it with a small and acceptable leakage inward.


The XL6 controls two fans using two PID loops. Smoothing filters are programmed in the controller software and the screen provides a graphical representation of the system with convenient monitoring and adjustment of the working parameters.

Screen 1
Screen 2
Screen 4