Patent GB-626223-A (GB)
Title: Improvements in or relating to means for regulating the temperature of superheat of a vapour
IPC: G05D23/185
Filed: 1946-10-04
Abstract: 626,223. Steam superheaters. BAILEY METERS & CONTROLS, Ltd. and PAYN, C. W. Oct. 4, 1946, No. 29625. [Class 123(iii)] [Also in Group XXIX] Apparatus for regulating the temperature of superheat of a vapour comprises a thermal element responsive to the temperature of the superheated vapour and operating a pilot valve which varies a loading pressure applied to a pneumatic relay, the pilot valve of the latter giving a control pressure which is applied to a device effecting regulation of the temperature of superheat, and the control pressure from the pneumatic relay is applied through a throttling device to a second pressure responsive element which reacts back on to the second pilot valve in the same sense as the loading pressure impulse applied by the first pilot valve. In an embodiment, the thermal element comprises a tube 5, Fig. 2, of steel and a rod 8 of invar or silica, and the movement produced by the thermal element is applied to lever 11 pivoted at 15. The free end of the lever carries an adjustable tappet 19 acting on the stem of a pilot valve 22 provided with a pressure-fluid inlet 23 and producing at the outlet 24 a pressure which varies according to the movement of the thermal element. Screw 19 provides a coarse adjustment of the datum point and a fine adjustment is provided by a screw 18 acting on an extension 11" of lever 11. A bellows 33, Fig. 1, responsive to the pressure produced by pilot valve 22 actuates a relay pilot valve 46 through a floating lever 36, bell-crank 39, and link 47. Lever 36 is also pivoted to a lever 35 pivoted at 37 to a frame 38, the latter being pivoted at 54 to a pivoted plate 48 and being adjustable in position on plate 48 to vary the sensitivity of the relay by means of a screwed pin 55 carried by the frame which can engage in holes 56 in the plate. Manually actuated gears 52 in engagement with plate 48 enable the datum point of pilot valve 46 to be varied. Air under pressure is applied at 57 to pilot valve 46 and the pressure variations produced by this valve are applied to a bellows 62 to actuate a further pilot valve 69 controlling a double acting piston and cylinder 63 which is connected to a valve 4 of an attemperator in which the cooling fluid is separated from the superheated steam by cooling surfaces. A follow-up is obtained by allowing the movement of the piston to act back through the bellows loading spring 78 so as to re-centre valve 69. The control pressure variations produced by valve 46 are also applied through a restriction 60 to a bellows 43, and the resulting movements of the latter are applied through a lever 41 and an abutment or fulcrum 42 to a bell-crank 40 on which bell-crank 39 is pivoted. The movement thus given to valve 46 increases the movement originally given to it by bellows 33, this action being provided in order to prevent overshooting because the increased movement will take effect as the valve 4 is on the return movement to normal position after a control movement to correct an irregularity in the temperature of superheat. The positon of abutment 42 along the levers 40, 41 can be varied. In a modified system, a tubulous vapour generator 80, Fig. 5, is provided with a convection superheater section 81 the flow from which divides and passes through radiant superheater sections 82<SP>1</SP>, 81<SP>11</SP> before re-combining and passing to the outlet 30. The temperature at the outlet is detected by a thermostat 1 which controls a regulator 3<SP>1</SP> through a relay 2 as shown in Fig. 1. Regulator 3<SP>1</SP> actuates the valve 4' of an attemperator 83<SP>1</SP>. The rates of vapour flow in the two paths, as indicated by the vapour pressures, are applied to a differential relay 84, such as described in Specification 461,389, and the control pressure produced by this relay is applied, along with the control pressure produced by relay 2, to an averaging relay 86. The latter controls a servomotor 3" actuating a valve 4<SP>11</SP> in an attemperator 83". The valve 4" is thus controlled partially by the rates of vapour flow in the two parallel superheaters 82<SP>1</SP>, 82<SP>11</SP>.