Butterfly valves are a flat circular disk mounted inside a tube which can be rotated 90 degrees and thereby either allow or prevent fluid from flowing through a pipe. When the valve is nearly closed it can act as a throttle which limits the flow. There are other valves working in a similar way, but the butterfly valve is the most common choice for large valves used to control liquids flowing through pipes with diameter of more than 100 mm. Such type of valves may be rotated by mean a motor or by other types of actuators.
Electric actuators are one type of actuator used to rotate valves from closed to open position and any position in between, usually consisting of an electric motor combined with a gear so that the motor must rotate many times for the valve to rotate a quarter of a revolution.
It is preferable that the valve is unable to rotate the motor. This means that the valve should not move caused by the torque acting on the valve, like torque set up by the fluid flowing through the valve or torque caused by the valve sealing, even if the motor is turned off. For safety reasons it is usually best that the valve does not open or close if the electric power should disappear. Moreover, it is preferable not to have current flowing through the motor when it is standing still, something which would be necessary if the motor had to produce a torque to keep the valve in position. This may be achieved with a gear producing a considerably sized friction, or a friction break which the motor must overcome before it starts moving. Both solutions mean that the motor must be larger than strictly necessary because it must produce enough torque to overcome the break, in addition to the torque necessary to move the valve. It is also power inefficient and the friction will cause a lot of wear.
The present invention is motivated by a product made by Ringspann GmbH. A classic application of RINGSPANN™ irreversible locks is for the automatic locking of adjusting mechanisms. For such use the lock is seldom rotated more than a few revolutions and it is preferable that a considerable torque must be applied for the adjustment. An irreversible locks of this type have been attempted used between the gear and the motor in a butterfly valve actuator where the number of revolutions can be several hundred. Such irreversible locks will, however, create a lot of unnecessary friction, increasing the required size of the actuator motor and creating heat and wear which can cause problems.
Hence, there is a need for a mechanism preferably preventing the valve from rotating the motor. This means that the valve should not be move by a torque produced by the valve, such as a torque set up by the fluid flowing through the valve or torque caused by the valves sealing, even if the motor is turned off.
For safety reasons it is usually also a need for a mechanism preventing the valve from becoming open or closed, if the electric power should disappear.
Also it is a need for a system where there is no current flowing through the motor when it is standing still, something which would otherwise would have been necessary if the motor had to produce torque to keep the valve in position.
It is also a need for having a self lock mechanism preventing the valve from moving unless it is subjected to torque from the motor. For practical purposes this is a break which is turned off when the motor is turned on.
A further need is to have a self lock mechanism which is purely mechanical and that is activated and deactivated by the motor. It must also be very reliable.