GB1251883A - - Google Patents

Abstract

1,251,883. Valves. DANFOSS A./S. 16 April, 1969 [19 April, 1968], No. 19477/69. Heading F2V. [Also in Divisions G1 and H1] An actuator for a valve comprises a piston 4 which is displaceable by an electrically heated expansible material 2 and which acts upon a displaceable spindle 5, the piston and spindle being displaceable relatively to each other and a switch in the circuit supplying heating current to the expansible material being actuated in dependence on the relative displacement. The material 2 is heated by a coil 3 connected to supply terminals 24, 26 via switches 18, 21. A control switch 25 is connected in parallel with the switch 18 and an intermediate member 12 is spaced from the piston 4 and the spindle 5 by springs 11 and 13 respectively. A spring 9, which is stronger than spring 11 but weaker than the spring 13, biases a closure member 6 away from the valve seat 7, a flange 8 on the spindle abutting the valve housing 10. With the switch 25 open, the material 2 heats up thus displacing the piston 4 until the switch 18 is open. The heater current is therefore cut off and the valve remains in its open position. With the switch 25 closed, the spindle 5 is displaced against the force of the spring 9 to close the valve. Heating of the material 2 continues until the movement of the member 12 towards the spindle 5 against the force of the spring 13 opens the switch 21. In a modification, Fig. 2 (not shown), an additional switch actuated by the piston and a further control switch enable the valve to occupy open, closed or intermediate positions.