... downstream principle, pvc shutter or aluminum shutter, antioxidant, light weight, no distortion, open and close sweetly, prevent ... strength more high-gluten strength aluminum-magnesium alloy wheel, light weight, high strength, toughness good;5. 6 pcs ... durability;6. There are two types of fan house, slant wall type, upright wall type, could satisfy ... class: F grade. air cooling system for poultry house