The butterfly valve is mainly used for pressure piping when water is about to enter the turbine housing. The opening and closing commands are performed by the hydraulic system (ie the cylinder and the double acting piston in the cylinder). The movement of the shaft connected to the piston rod is linear (moving back and forth only), but the cam is used to convert the linear movement into rotational movement. The rotating cam is connected to the end of the butterfly valve on both sides of the pressure pipe. Thus the flow of oil in a particular direction will move the piston and thereby move the shaft, which in turn rotates the cam and thus rotates the valve's linkage to operate it.