The function of the fire-proof door sequencer is to close one door first, and then close the other door after a few seconds, so that the door can be closed smoothly, so that the fire door can play the role of fire prevention and partition. Fire protection requirements. With reference to the RDA-29L sequencer of Lelang Hardware, it is made of stainless steel 304, and its anti-corrosion, anti-rust and durable characteristics are deeply loved by consumers.