696,312. Interlocking valves. COOK, D. April 21, 1952 [April 21, 1951], No. 9348/51. Class 135 [Also in Group XI] A gas burner installation comprises a main burner 23, a pilot burner 5, a main gas supply pipe 1 incorporating a control valve 4 downstream of a double-beat valve 3, a beat 10 of which is adapted to be held open by electromagnetic means, e.g. a solenoid 7, under the control of a thermocouple 6 or other thermally responsive means associated with the pilot burner 5, and mechanical interlocking means between the valves 3, 4 adapted to ensure that gas may pass to the main burner only when the pilot burner 5 is alight. The said mechanical interlocking means includes a lever 15 pivoted to a member 15<SP>1</SP> depending from the casing of the valve 3, said lever being depressed to raise an arm 16 secured thereto which lifts the other valve beat 9 to close the latter against its seat whilst raising the beat 10 off its seat. The beat 10 is held open by the solenoid 7 previously energized by heating the thermocouple 6 by a gas poker 24 supplied through a pipe 25 connected upstream of the valve 3. The end of the arm 16 is received in an L-shaped slot in a drum 19 fixed to the plug of the control valve 4, so that the lever 15 can be operated only if the valve 4 is closed, when the arm 16 is movable in the vertical limb 18 (not shown) of the L-shaped slot 17, 18. The lever 15 is held depressed by engaging with a ratchet (not shown) thereon a detent 28 pivoted to the member 15<SP>1</SP>. With the valve beat 10 thus raised gas passes from the valve 3 through an opening 13 and a pipe 8 incorporating a valve 29 to the pilot burner 5, which is ignited by the gas poker 24. The valve 29 is disposed within the drum 19, and is operable only when the valve 4 is closed, by a key inserted through a hole 30 in the drum. On ignition of the pilot burner 5 the gas poker 24 may be extinguished and the lever 15 released from the detent 28 to be forced upwardly by internal spring means (not shown), and the valve beat 9 is forced downwardly by an associated spring (not shown) to permit gas to pass through the valve 3 to the valve 4. The latter cannot, however, be opened until the arm 16 is freed from the vertical slot limb 18 in the drum 19 by pulling the lever 15 upwardly so that the arm 16 can pass into the horizontal slot limb 17 when the valve 4 is turned to the open position. On thus opening the valve 4 gas passes to the main burner23 to be ignited by the pilot burner. Should the control valve 4 be inadvertently opened first the arm 16 being located in the horizontal slot limb 17 prevents opening of the valve 3. In the event of failure of the pilot burner flame the thermocouple 6 cools to de-energize the solenoid 7 and close the valve beat 10 to cut off the gas supply to both main and pilot burners. The pilot burner 5 comprises an L-shaped tube which may be slotted or perforated to ensure a continuous flame along its entire length, and has a portion exposed externally of the wall of the furnace 2 to be heated by the main burner 23, to provide a visible indication that the pilot burner is or is not alight, the remaining portion of the tube being disposed internally of the furnace wall. The pilot burner flame is thus protected against complete extinction by an internal or an external draught. In a modification a further stop cock is provided upstream of the valve 3 and has a slide bar connected with its valve plug for co-operation with a flat surface on the drum 19 to prevent opening of the valve 4 if said additional stop cock is closed, and to prevent closing of said additional stop cock if the valve 4 is open. The valve 29 is omitted from this modification.