Patent GB-485162-A (GB)
Title: Improvements in or relating to an automatic control system
IPC: G05D16/18
Filed: 1936-11-11
Abstract: 485,162. Fluid - pressure servomotorcontrol systems ; hydraulic couplings. ELECTROFLO METERS CO., Ltd. (Republic Flow Meters, Inc.) Nov. 11, 1936, No. 30768. [Classes 69 (ii) and 135] An automatic control system for regulating a variable condition such as pressure comprises a fluid coupling 12 connected to a unit such as a blower at which the variable condition prevails, and valves 32, 33 which regulate the amount of fluid in the coupling to determine its speed transmission ratio, and are operated by an automatic regulator which acts through a dashpot device 41, 42 in the case of large or sudden variations in the controlled condition, and through a cam device 80 in the case of small or slow variations. The blower (not shown) is driven by a constant speed motor through the fluid coupling 12, Fig. 2, the amount of fluid in which is controlled in accordance with the blower discharge pressure so as to accelerate or decelerate the blower and thus restore the discharge pressure to the predetermined value. The coupling is supplied with oil or other liquid from a tank 15 by a pump 16 through pipes 17, 19. Liquid discharged from the coupling through ports 22 is collected by a stationary scoop tube 23 and returned to the pump inlet by a pipe 24. The pump is fitted with a relief valve 18 and the liquid in the coupling is cooled by a radiator 25. The valves 32, 33 in the pipes 19, 24 respectively control the supply of liquid to the coupling and the discharge therefrom. These valves are actuated by levers 34, 35 respectively and moved to the closed position by adjustable springs 37. The ends of the levers overlap and lie in the path of a roller 38 on a piston rod 39 so that the valve 33 is opened when the piston rod is raised whilst the valve 32 opens when the rod is lowered. The piston rod 39 is moved in accordance with changes in the blower discharge pressure by an automatic regulator such as that shown in Specification 463,326 or in Specification 463,549. The regulator operates the rod 39 through the dashpot device which comprises a cylinder 42, a piston 41, and a byepass 44 adjustable by a valve 45. The regulator shown is similar to that described in Specification 463,326 and has a casing 46 containing a diaphragm exposed to the blower discharge pressure by a pipe 47. Through a rod 49 and a yoke 48 the diaphragm controls a spring-loaded lever 51 carrying a valve 57 regulating the discharge of fluid from an orifice 58 communicating with space below a differential piston 61. The space above the piston is supplied with pressure fluid by a pipe 62 and communicates with the underside of the piston by a restricted passage 64. The rod 68 of the piston 61 acts to restore the lever 51 to its original position through a dashpot 69 having an adjustable byepass 71. The piston 61 through a floating lever 74 pivoted to the rod 68, operates a relay valve 76 controlling a power piston 77 connected to the dashpot cylinder 42 by a rod 43 connected to the floating lever 74 by a rod 73 so as to return the relay valve to its original position. To prevent under-control due to the valve 45 being opened too wide and to ensure that the regulator returns to its central position, the dashpot cylinder 42 is connected by a link 78c to an arm 79c moving the cam device 80 about a fixed pivot between the overlapping ends of the levers 34, 35. Only when the cam is horizontal as shown in Fig. 3 are both valves 32, 33 closed and regulator centralized.