The headstock of gate valve is gate; the direction of motion of gate is vertical with that of flow. Gate valve can be only full open and full close, but cannot regulate or throttle.The gate has two sealing surfaces; normally, these two sealing surfaces form wedge; the angle of the wedge differs according to gate valve technical diameter, 50°normally. The temperature of applicable medium of gate valve is less than 425 degree C. The gate of wedge gate valve can be processed to be one whole body, this type of gate is called rigid gate. The other type of gate is called flexible gate, the flexible gate can have micro deformation to make up the tolerance of the sealing surface  of the gate in the processing.