position of the spring tail 90 by a fixed latch the resulting torsional forces on the opposite ends of the spring 88 force it to radially constrict into locked frictional engagement with the annular surface of the fixed friction drum 87 with one axial section of the spring 88 fixedly positioned on the fixed drum 87 the other end tail 85 serves to hold or lock the control shaft 5 at a fixed loaded angular position the angle between the spring tail 90 and the spring tail 85 and thus control shaft 5 being constant and predetermined thus the angle at which the loaded control shaft 5 is held or locked is determined by the angle at which the spring tail 90 is restrained or latched within the counter mechanism referring to fig3 and 5 respectively the control shaft 5 is locked in a 34 valve full open 34 position when the spring end tail 90 is restrained at the 1 o 39 clock position the shaft is locked in a 34 valve partially open 34 position when end tail 90 is restrained at the 2 o 39 clock position and the shaft moves to a 34 valve closed 34 position when the end tail 90 is allowed to rotate beyond the 2 o 39 clock position to the 3 or 4 o 39 clock position the restraining force required to hold the spring tail 90 in position to lock the spring 88 and hold the control shaft 5 is far less than the angular loading force applied by the valve 8 to the control shaft most of this force is received by the fixed drum 87 with which the spring 88 is in locked engagement thus only a relatively small.