1. The most reliable modern main fans have a probability of trouble-free operation of Pf(720)=0.76. 2. Analysis of the reliability of MVF as systems with recovery shows that the trouble-freedom of the system with reserve (on the assumption that the switchover device is absolutely reliable) is very high [Pc (720)=0.995], despite the greater complexity of the controlled fans. 3. The switchover device has lower trouble-freedom, Py (720)=0.89. Consequently, we should first seek to improve the reliability of the switchover device. 4. The reliabities of fan plants can be raised by the use of controlled fans for reversing the air stream, which permits us to dispense with reversing valves with drives and their shutters, and consequently raises the reliability of the switchover device.