GB1381558A - Thermal actuator - Google Patents

Abstract

1381558 Thermal responsive devices DANFOSS AS 22 Sept 1972 [22 Sept 1971] 43978/72 Heading G1D [Also in Division F2] A thermal actuator for a valve 6, 7, has formed therein a working chamber A containing a vaporizable liquid 21 and an equalizing chamber B, the two chambers being in selective communication with one another by way of an aperture-defining seat 14 and the channels formed in a valving- member 15, such channels being defined by the polygonal cross-section of the valving-member and being in communication with transverse passages 16. The stem 5 of main valve-member 6, is connected to an interior housing 11 which depends from a bellows 4 and which houses an electromagnetic coil for actuating valving-member 15. The lowermost portion of housing 11 carries an electric heater coil 17. In the state of the actuator shown, the two chambers A and B are in communication with one another and so there is no net pressure differential across the bellows wall 3, there being, in such circumstances, a net downward force on valve stem 5 due to the action of spring 12. On activating the heater 17 and closing magnetic valve 14, 15, the vaporizable liquid 21 (e.g. a fluorochlorohydrocarbon) becomes heated and the vapour thereby generated eventually produces a force greater than, and opposite to, the force of spring 12, thus opening valve 6. If the latter is then to be closed rapidly, magnetic valve 14, 15 is opened and so the pressure in chambers A and B becomes equalized thereby rendering spring 12 effective in rapidly moving closure member 6 into engagement with seat 7. On condensing in chamber B, the condensed vapour flows back into chamber A via passages 16, possibly assisted by a small pump. A pressure sensor 20 cuts-off the current to heater 17 when the pressure exceeds a predetermined value. Alternatively a limit position switch may be used. In a modification Fig. 2 (not shown) the chambers A, B are separated by a rolling diaphragm (29) supporting a movable wall (33) which is frusto-conical to direct condensed vapour from chamber B back to chamber A. Parts of the electromagnetic valve (35) and parts (23, 24) of the actuator housing may be of moulded plastics material, whereas the top (25) of chamber B is of metal to assist condensation.