Patent GB-685499-A (GB)
Title: Improvements in fluid-pressure controlling or regulating systems
IPC: F15B9/06
Filed: 1951-02-13
Abstract: 685,499. Fluid-pressure servomotor-control systems ; hinged valves. MASON-NEILAN REGULATOR CO. Feb. 13, 1951 [Feb. 28, 1950], No. 3509/51. Class 135. A fluid-pressure controlling or regulating system includes a gimbal pivotally mounted on a support, a second gimbal pivotally mounted on the first so that the axes of the two pivotal mountings intersect, a valve for varying the pressure in the system, and connected to the second gimbal, and one of the gimbals is responsive to changes in the value of a variable, whilst the other is responsive to pressure changes in the system. In an embodiment, for controlling a temperature, a thermal bulb is connected by a flexible capillary 29, Fig. 1, to the fixed end of a Bourdon tube 11 of which the other end is pivoted in the tube supporting frame 18 and is connected by a lever 22 and link 70 to the inner gimbal ring 61. The datum temperature is set by rotating the frame 18 through gearing 28, and this set temperature is indicated on a scale 26. The outer gimbal ring 60 is pivoted in a frame 64, secured to the back-plate 10 of the apparatus, at right angles to the pivoting axis of the gimbal ring 61. The pilot valve comprises a nozzle 15 secured just below the centre of the gimbal rings and obturated by a flap 14 pivoted in a stirrup 85 extending radially from shaft 86 in line with the nozzle. Thus, by turning a hand wheel 95 on shaft 86, the flap 14 can be rotated around the nozzle so that an extension on the outer end of the flap can be made to contact the inner gimbal ring at any point of the latter. The flap is spring-pressed into contact with the gimbal ring. The hand wheel 95 carries a scale which, in conjunction with a pointer 107, shows the position of the flap around the gimbal ring, and click stops are also provided on the wheel to give an indication when the flap passes from one sector to another on the gimbal ring. Air under pressure is supplied to the nozzle through a pipe 54 and past a restriction 53, and the variations in pressure downstream of the restriction which are produced by movements of flap 14 are communicated to a diaphragm motor 44, the latter actuating a valve 41 controlling the flow of a fluid to maintain the variable at the desired value. To provide a follow-up, the pressure applied to the diaphragm motor is also applied to a bellows 12 which contacts a projection 81 on the outer gimbal ring and moves the latter in such manner that the flapper 14 is moved in the direction to reset or neutralise the valve. When the flapper 14 is located in the D.P. sector of the gimbal ring 61, Fig. 7, an increase in the value of the variable (temperature) will produce an increase in the output pressure applied to the diaphragm motor, but when the flapper is adjusted to be in the R.P. sector, an increase in the variable in the same sense as before produces a decrease in the output pressure of the system. These two conditions are the direct acting and reverse acting, respectively. If the flapper is adjusted to lie in the D.S. and R.S. sectors, direct and reverse action, respectively, will be produced as before, but the flapper will not give a continuous regulation but will snap over from one limiting position to another as the limits of the range over which the temperature is to be controlled are attained.