... lubricated upper and lower ball bearings to ensure long life without maintenance, no need to replace the zeroCases, the U.S. PEER, UBC, ... is also self-operation.3, green ventilationUse of natural wind-driven principles, not the use of motor power, to avoid the cost ... of running electricity-free, non-stop self-turbine ventilatorRotation, so silent no noise when running.4 ...