Patent GB-846866-A (GB)
Title: Improvements in or relating to gas control mechanisms
Filed: 1955-08-08
Abstract: 846,866. Fluid-pressure servomotor-control systems. GREAVES, A. H. Aug. 8, 1956 [Aug. 8, 1955], No. 22794/55. Class 135. A gas-control mechanism for gas-fired heating equipment comprises a main gas valve 5 connected axially to two transverse flexible diaphragms 6, 11 of different area separated by a space 12 open to atmosphere at 13, the smaller diaphragm 11 being disposed between the valve and the larger diaphragm 6, and a weep gas system comprising a valve-actuating compartment 1a adjacent the larger diaphragm connected through a small weep jet 10b to the inlet side of the main valve and also through an outlet 14 to one or more weep gas control devices adapted to vary by one or more auxiliary weep gas valve mechanisms the weep gas pressure in the compartment la. The arrangement is such that the opening of any one of the weep gas valve mechanisms causes the outlet 14 to be opened so that pressure in the chamber 1a falls and the valve 5 closes or moves towards the closed position. The net upward force on the diaphragms normally keeps the valve 5 open. The valve 5 is arranged in a valve chamber 4 the outlet from which is controlled by a pressureregulating valve 7 actuated by the pressure in the outlet 3 on a weight-loaded diaphragm 8. The chamber 1a has in addition to the outlet aperture 14 leading to one or more weep gas control devices and also an outlet 28 controlled by a valve 27. The valve 27 is carried on a diaphragm 26 separating chambers 25, 25a. The chamber 25 has a restricted connection 10a with the gas inlet 2, an outlet aperture 16 leading to a pilot protection device, and a further outlet controlled by a valve 22. The chamber 25a has a vent 15 to atmosphere. The valve 22 is operated by a diaphragm 20 separating chambers 18, 18a. Chamber 18 has a vent aperture 17 and chamber 18a has a connection 19 which may be connected with the water space of a boiler so that the pressure below the diaphragm 20 is a measure of the liquid level in the boiler. To enable the mechanism to be responsive to steam pressure as well as water level, a spring-loaded valve 23 is arranged in the valve 22. The valve 23 opens when the steam pressure exceeds a predetermined maximum, the valve 22 then being closed. To enable the mechanism to respond to low water level even when the steam pressure is high, the boiler is provided with a relief pipe. This pipe is of sufficient length to accommodate a column of water equal to the maximum steam pressure and its lower end is normally immersed at a level below the minimum water level, its upper end being open to atmosphere. Alternatively the connection 19 may be made to an air pressure vessel or duct. In another arrangement the connection 19 is connected to the gas inlet 2 so that if the gas supply pressure falls below a predetermined value, the valve 5 is closed automatically. To prevent any part of the system from overheating, weep gas is conveyed by a pipe to the part to be protected, the outer end of the pipe being sealed by material which fuses at the desired maximum temperature. A thermostatically controlled weep gas valve may be provided, this being responsive to the temperature of the heated medium and arranged to open this valve as the temperature rises above a pre-set value. The outlet 16 may be connected to a pilot flame protection device comprising a pilot burner 29 the flame of which lights the main burner and also impinges on a temperature-sensitive element 30. When the pilot flame is established, the element 30 is deflected and a spring-pressed member 33 forces a spring-loaded ball valve 32 to its seat. On failure of the pilot flame, the valve 32 opens, and a passage 35 connected to the outlet 16 is opened to atmosphere. Gas is initially supplied to the burner 29 through a push-operated ball valve. Thus once the pilot burner is lighted its gas supply is maintained by the by-pass, and the push-operated valve may be released. To prevent the valve 5 from being re-opened by the diaphragm 26 when a fault or failure to which this diaphragm is responsive is rectified, a pivoted member 45 is provided between the diaphragms 6 and 26. The member 45 must be reset by the push rod 44 before the diaphragm 26 is again operative on the valve 5.