GB909997A - Improvements in or relating to gas flow control mechanisms - Google Patents

Abstract

909,997. Fluid-pressure servomotor systems. GREAVES, A. H. Jan. 20, 1959, No. 2139/59. Class 135. A gas control unit for a burner comprises a gas control valve 5 rigidly connected to two diaphragms 11, 6a of unequal effective area separated by a space 12 open to atmosphere and a distribution chamber 19 supplied with gas fed from the main inlet 2 via a passage 18 closed by a loose ball valve 18a and a passage 17 closed by a spring-loaded loose ball valve 24 and feeding a pilot burner 31 through passage 25, a control chamber 21 below a diaphragm 22 by passage 10a and a control chamber 6 below the diaphragm 6a by a bleed passage 10. The chamber 6 is connected to a number of control valves 35 such as thermostats and the space 21 is connected to further control devices such as a flame failure device as described in Specification 846,866 and a fusible plug to prevent overheating. A dead-weight loaded pressure regulating valve 7 may be provided in the inlet. In operation, when all of the control valves are closed and the burners extinguished, valves 5, 18a and 24 are closed and valve 20 connecting chamber 6 to atmosphere is open. To operate the unit the starter valve 24, which may be situated remotely from the main unit, is actuated manually or electrically to allow gas to enter the chamber 19 and then pass to the pilot burner, to chamber 21 to close the valve 20 and open valve 18a, and to chamber 6 to open the main valve. On closure of the starter valve, the valve 18a having been opened to inlet gas, maintains these conditions. On opening of the control valves 35, the main valve closes an amount according to the opening thereof and even on complete closure of the main valve the pilot burner stays alight. If, however, either of the control devices 33 are operated to release pressure from the chamber 21 the whole unit closes and the starter valve must be used to enable the main burner to be relighted. The construction is such that any leakage of a diaphragm, or a choked weep passage causes closure of the unit as does a reduction in supply pressure below a minimum amount.