The motorized gate valve is activated to close the furnace after the retraction of the filter. When locked, it must ensure a good tightness of the oven for any pressure below 3 bar, when opened it has to free the passage of the filter. The gate valve system is a specifically developed device (SEP) which is mainly composed of the gate valve (GV) itself, the mechanism (GVM) and the motor (GM). A guillotine valve has been preferred to a spherical valve concept which implied a too long stroke for the filter. The closing and locking operations of the valve is as follows; first, the gate valve is pushed by a screw driven by the motor, from its retracted position towards closed position. When the gate valve reaches this position (the extremity of the clapet against the body) the gate valve inside mechanism activated by the screw makes its thickness increase until the movement is stopped by the main body of the valve. At that time, a O-ring gasket which groove is machined on the top clapet, is crushed between the oven collar and the clapet. This O-ring is made of Kalrez elastomer since tests have shown that a metallic gasket could not satisfy the high tightness requirement During the closing motion of the valve, its stroke is consequently decomposed in two parts ; the first part, 23 mm along the GV screw axis, will permit to close the access of the filter to the sampling tube (closing phase) ; the second part, 5 mm along the same direction, will serve to bring the gate valve against the bottom collar of the oven body (locking phase). The operational requirement is a complete activation within less than 5 s.

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