GB1521972A - Pressure control for variable pressure boiler - Google Patents

Abstract

1521972 Pressure control in variable pressure steam boilers J W CARTER Snr and J W CARTER Jnr 29 July 1975 31626/75 Heading F4A A steam boiler of water tube construction (preferably a monotube boiler such as can be used in vehicle power plant) has a throttle valve 11 to vary the steam pressure output and a pressure differential sensing means 36 located across the valve to operate a combustion fuel control for the boiler; the sensing means being designed at a particular throttle setting to maintain a set pressure differential across the valve 11 as well as to prevent a dangerous build-up of boiler output pressure. As shown in Fig. 2 a drum member 16 having an aperture 17 and rotatably movable on a fixed drum member 18 with an aperture 19 can be adjusted by a motor 29 (via a belt 31) to increase or decrease the boiler air supply which enters via the apertures and has a cam 20 which acts via follower 22 and cable 26 to simultaneously adjust a fuel valve assembly 28. The sensing means 36 comprises a cylinder 37 supported for axial movement, a fixed piston rod 41 fast with a small piston 53, a large piston 49 loosely located on piston 53 for limited axial movement thereon, and spaces on either side of piston 49 which are interconnected via the throttle valve and high and lower pressure steam lines 65, 67. The pressure differential tends to urge piston 49 to the right against the force of spring 61 and an attached rod 50 acts on a spring element 76. Movement of the element 76 to the right closes switch 35 to turn member 16 in a direction to decrease boiler combustion air and a lever arrangement 84, 85 secured to member 16 pivots bracket 74 at 79 (on which switch 35 is mounted) away from element 76 to open switch 35. The magnitude of the fuel and air response is therefore directly related to the magnitude of the differential and relative longitudinal adjustment of levers 84, 85 controls this magnitude. Reduction of the differential causes the spring 61 to move piston 49 to the left and element 76 to close a switch 34 to turn member 16 in the reverse direction. In addition to the movement of the piston a sufficiently large boiler output pressure (on line 65) causes the whole cylinder to move to the right against a spring 37 and this will act to close switch 35 and reduce boiler air and fuel.