Abstract: A yawing system for a wind mill consists of two yawing motors (9, 11) acting on a toothed rim of the yawing bearing. On each its drive shaft (21) the motors (9, 11) are provided with a free wheel (23) and an electromagnetic friction brake (25). The free wheel devices (23) are directed opposite each other. A control system operates in a passive state in such a manner that the motors give opposite and relative to the braking moment of the brake (25) of a second motor smaller torque thereby avoiding dead clearance between drive wheel (15) and toothed rim (17) while at the same time keeping the generator housing (5) of the mill at rest. In the active state of the control system both brakes (25) are disengaged and both motors give a higher torque in the same direction. The system acts as a shock absorber by loads exceeding the fixed slip moment of the friction brake (25).

Abstract: In order to control the tightness of a central heating system (10, 11) which may be connected to a district heating system (1, 2), the system is provided with a flow meter (8, 9) and a valve (6, 7) in the flow (3) and return pipes (4), respectively. Hereby it becomes possible to monitor the liquid flow through the flow meters (8, 9) and in a control unit (15) to compare the signals from the flow meters (8, 9) in order subsequently to produce a signal for an electric motor on the inflow valve (6) when a certain limit value is exceeded in order to shut off the flow of water into the system (10,11) and to a signalling device (16), if any.