and close the circuit which connects the liquid pressure supply and return sides i e at p and t and the liquid pressure motor 11b in the case of fig8 a the electromagnetic valve 44b closes that circuit and blocks the communications between the passages 46a and the vane 42a and between the passage 46b and the vane 42b so that the supply of liquid pressure to the liquid pressure motor 11b is stopped as shown in fig8 b when the electromagnetic valve 44a is energized to close the passages 46c and 46d whereas the electromagnetic valve 44b is energized to open the circuit thereby couple the liquid pressure supply sides i e the p and t sides to the liquid pressure motor 11b the liquid pressure is introduced into a passage 46e of the motor and out of a passage 46f of the motor so that the liquid pressure motor 11b is rotated clockwise this rotation is transmitted to the rotary valve stem 40 through the gears 12c and 12d of the liquid pressure motor 11b the prime mover 18 the follower unit i 19a and the shaft 17b which together form a mechanical transmission mechanism so that the rotary valve stem 40 also rotates clockwise when the rotation is continued past 180 u00b0 as shown in fig8 c the vane 42a i e the reference point passes through the passages 46b of the housing 41 if at this time the electromagnetic valves 44a and 44b are.