The filter press is one of the key equipments in discharging of dry red mud in Bauxite aluminium plants.Due to the influence of the working environment

the flap system driven by harmonic motor is hardly to normal use for its high failure rate.Through the reform of flap driven by hydraulic system

this problem is successfully solved.The reform of single cylinder driving system is introduced

the synchronicity of four bar mechanism is analyzed

then the conclusion that the flaps could not always synchronous

but can start at the first position synchronously and stop at the end position synchronously is given.Finally

a sufficient condition of two synchronization at the first position and the end position in four bar mechanism design is given.