928,018. Gas-turbine engine reheat apparatus. ROLLS-ROYCE Ltd. Nov. 14, 1961 [Nov. 15, 1960], No. 39256/60. Class 110 (3). A gas-turbine engine comprises a compressor, main combustion equipment, a turbine and an exhaust duct, reheat combustion equipment being mounted in the exhaust duct and having a fuel conduit leading thereto from a source of fuel. Control means are provided either to permit or to cut-off a flow of reheat fuel, also means for supplying to the main combustion equipment a quantity of fuel to form a " hot streak " adapted to ignite the reheat fuel at the reheat combustion equipment, the " hot streak " supply means being brought into operation for a limited period upon the control means being set in the operative position and a flow of reheat fuel being supplied to the reheat combustion equipment. The reheat control device is shown in Fig. 2 and comprises a reheat fuel pump 22 of the gear type which takes its suction through line duct 21 and discharges through ducts 24 and 25 to a fuel metering valve which comprises a valve member 27 disposed within a bore 26. The valve member 27 comprises an annular recess 31 which communicates at all axial positions of the valve member with the duct 25 and with a metering orifice formed by ports 30, the area of which increases towards the right. Thus fuel passes through duct 25, annular recess 31, metering orifice 30 to the duct 60 and may pass through the pressurizing valve 62 to the line 15 and so to the reheat fuel burners. The left-hand end of the valve member 27 is acted upon by air pressure #P 2 , air at compressor discharge pressure P 2 being supplied through duet 46 and passing under control of the needle valve 51 to the ducts 54, 55 leading to the valve bore 26. The needle valve is controlled by a pinion 53 which is rotatable by the reheat control lever. The righthand end face of the valve member 27 is acted upon by air at pressure P 4 , the pressure in the engine jet pipe, which is communicated through duct 57. This end face of the valve member is also acted upon by a spring 37. The duct 54 communicates with the duct 57 by way of a duct having a restriction 56. A throttle or bypass valve 66 is provided and serves to maintain the pressure drop across the metering orifice 30 substantially constant, at say 50 p.s.i., the valve 66 being mounted in a bore 65 which communicates at its left-hand end with the pressure of fuel in duct 25 upstream of the orifice and at its right-hand end by way of ducts 77, 76 with the pressure of fuel in the duct 60 downstream of the orifice. The valve 66, which is also acted upon at its right-hand face by a spring 74, controls the outlet area of the port 72 so that if the pressure difference across the metering orifice is too high, the valve 66 is moved to the right to open the port 72, whereby fuel from the pump outlet 23 is bypassed through ducts 81, 83, 84 back to the suction side of the pump. If the pressure drop across the metering orifice is too low the valve tends to close the port 72 whereby the pressure differential is restored. Fuel also passes from the bore 65 to the line 105 which leads to an assembly to be described below. A shut-off cock 90 is provided and controls communication between ports 93, 94, the cock being shown in the " reheat operative " position in which such communication is not established. When the cock is moved to the right by means of the pinion 98, the annular recess 91 in the cock establishes communication between the ports 93, 94, whereby fuel from the outlet of the pump passes through duct 95, port 94, recess 91, port 93, duct 81, passage 83, duct 84 and passage 21 back to the suction side of the pump. A solenoid-operated valve 101 is provided, the valve member being acted on by a spring which tends to close it. When reheat is not selected, the solenoid is energized and the valve is in the open position shown whereby fuel in the duct 60 will not act to open the pressurizing valve 62 but will pass through ducts 77, 84 back to the suction side of the pump. When reheat is selected the solenoid is de-energized and the valve 101 is moved to the closed position by the spring. Fuel in the duct 60 then acts to open the pressurizing valve 62 and passes through the line 15 to the reheat burners. When reheat is selected, fuel pressure in the line 105 acts against the left-hand face of the piston 114 and moves the piston to the right against the loading of the spring 120, and as the piston moves it causes fuel contained within the piston to pass through the duct 128 thereby causing the valve member 126 to open against the loading of its spring. The fuel thereupon passes through the duct 18 to the main combustion equipment where it burns and causes a hot streak which acts to ignite the fuel which has passed simultaneously to the reheat combustion equipment. Continued movement of the piston 114 to the right causes the piston to open the port 112 as shown in Fig. 4, and high-pressure fuel then passes to the right-hand side of the valve 126 which therefore closes and no further fuel passes to the line 18. The piston now engages the valve 123 thus closing the bore 115 in the piston end wall. When reheat is switched off, the fuel pressure in the line 105 will fall to that of the pump suction, and the piston 114 will thereupon be moved to the left by means of the spring 120. As it does so, fuel will pass through the bore 115 so as to fill the space within the piston so that when the piston again reaches the position shown in Fig. 2, it will be filled ready for the next " hot streak." The metering valve 27 and the by-pass valve 66 are arranged to be rotated continuously during operation so as to prevent sticking. An alternative embodiment of the valve assembly 107 is shown in Fig. 5 and comprises a valve body 141 which communicates with the fuel line 105 shown in Fig. 2. The assembly 141 is arranged to discharge a " hot streak " of fuel to the main combustion equipment by way of a duct 184 which communicates with the fuel line 18 (see Fig. 2). The valve body 141 has mounted therein a fixed sleeve 142 which has ports 143 therein, the ports communicating with the fuel line 105 by way of duct 140. The sleeve is also formed with ports 171 which communicate with a duct 172 which in turn communicates with further ducts 173, 174, the duct 174 being formed in a cylindrical member 154 secured within the valve body 141. A hollow piston member 147 is mounted within the fixed sleeve 142, the piston being loaded towards the left by means of a spring 153 which bears against the cylindrical member 154. The piston is formed with a circumferential recess 170 also with ports 164, and carries a plug 151 which is formed with an axial bore 152. A fixed sleeve 156 is disposed within the cylindrical member 154 and is formed with bores 190 and 185. A flow-control valve 177 is disposed within the sleeve 156 and is urged by a spring 180 towards the closed position against the valve seat 181 so as to close off the outlet passage 184. A valve member 160 loaded by a spring 162 is also mounted in the cylindrical member 154 and is adapted when the piston 147 has moved to its right-hand limit to engage the plug member 151 so as to close the bore 152. The valve is shown in the position before reheat is selected, the interior of the piston being filled with fuel at low pressure. When reheat is selected, high-pressure fuel is communicated to the line 105 and passes by way of ducts 140, 144 to the left-hand side of the piston 147 which thereupon moves to the right against the loading of spring 153 and as it does so it causes the fuel contained therein to pass through the duct 186, recess 187 and ports 190 to the right-hand side of the flow-control valve 177. The valve is therefore moved to the left against the loading of spring 180 and the fuel then passes through the duct 184 and line 18 to the main combustion equipment to provide the " hot streak " which acts to ignite the reheat fuel. When the piston reaches its righthand limit of travel, the annular recess 170 therein establishes communication between the ports 143, 171, whereupon high-pressure fuel from the line 105 passes through duct 140, port 143, recess 170, port 171, ducts 172, 173, 174 to the annular recess 155 and thence through the ports 185 to the space within the flow-control valve 177. The valve is therefore returned to the closed position and no further fuel passes through the duct 184 and line 18 to the main combustion equipment. Fuel from the duct 173 also passes through filter 175 to duct 176 and so to the drain passage 166 and line 167 back to the suction side of the pump 22. The space within the piston 147 is also connected to the drain passage 166 when the piston is at its right-hand limit of travel, by way of the ducts 164, 165. In this position of the piston the plug 151 engages the valve member 160 and so the axial bore 152 is closed off. When reheat is switched off, the pressure of the fuel in line 105 falls to drain pressure and this reduced pressure is communicated to the left-hand side of the piston 147, whereupon the spring 153 acts to return the piston to its lefthand limit of travel as shown in Fig. 5, the interior of the piston being refilled with fuel which passes through the bore 152.