Alternate vent system includes Vent gear motor, drive shaft, rail vent rack and pinion, shaft supporter, wheel supporter, handspike,supporting ... wheel,rack and pinion connectors etc. It is mainly used for Venlo greenhouse roof ventilation, the greenhouse air circulation could ... Vent RackCLJC-1050L=1050 mmALternate Vent RackCLJC-1200L=1200 mm Rail Vent Rack and Pinion