Patent GB-465530-A (GB)
Title: Improvements in air actuated apparatus for effecting automatic control action in response to variations in a physical condition
IPC: G05D23/12
Filed: 1935-12-04
Abstract: 465,530. Fluid - pressure servomotor - control systems. JAMES, R. W. (Brown Instrument Co.) Dec. 4, 1935, No. 33599. [Class 1351 An air-actuated control instrument, Figs. 1, 2, 3, for effecting automatic control action in response to variations in a physical condition such as temperature, pressure, liquid level or velocity comprises a control pressure space and a floating lever such as C<4> for operating a valve or flapper D which controls the pressure in the said space, the lever being movable about one pivot C<6> by means responsive to the physical condition so as to effect a change in the control pressure and further means being provided for moving the lever about a second pivot C3‹ in response to the said pressure change in a direction tending to neutralize the said pressure change and subsequently giving a slow return movement. The instrument is shown in Fig. 1 applied to the control of a fuel supply valve a in accordance with the temperature of a furnace A. A thermal feeler b actuates a Bourdon tube B the movable end of which is connected to a bell-crank lever B<4>, Fig. 1, which lever is also linked to a bent lever C<1> having an adjustable fulcrum C<2>. A link C<3> connects the lever C<1> to a three-armed floating lever C<4>, the short arm C<7> of which has an adjustable pin C<8>, Fig. 3, which actuates a spring-urged flapper D pivoted at d. The flapper D controls the nozzle end E of a pipe EF communicating with an air supply pipe F<2> through a coiled capillary tube F<1>. The restricted air supply is also in communication by a pipe F<3> with a chamber F<4> containing two concentric bellows F<5>, F<50> with a common movable head. The space between the bellows is vented and the inner bellows chamber forms part of a chamber F<10> containing a spring-urged relay valve device. This device comprises a disc F<7> controlling the air supply to the chamber F<10> through a nozzle F<8> and a capered nut F<70> controlling the exhaust therefrom. The position of the flapper D determines the pressure in the chamber F<4> the bellows device in which actuates the relay valve device to generate a higher pressure in the chamber F<10> in inverse proportion to the areas of the two bellows. The control pressure in the chamber F<10> acts on the motor a<2> of the valve a through a pipe aF so as to shut down the valve as the furnace temperature rises. The control pressure also acts on the larger of two concentric bellows 9<2>, GA secured to a fixed head GH<1>. A rod AB rigidly connects the movable end of the bellows GA to the corresponding end of the inner HA of a similar pair of bellows HA, H<2> connected to a head GH<3>. The sets of bellows have casings GH<2>, GH<4>, the former being exposed to the control pressure and the latter vented to the atmosphere. An interchangeable loading spring G<3> acts on the bellows H<2> and springs GA<3>, HA<3> resist the contraction of the smaller bellows GA, HA respectively. The spaces GA<1>, HA<1> between the sets of bellows are filled with an incompressible fluid such as oil or water and communicate with one another through passages GH<5>, GH<6> under the control of a screw-down throttling valve, the actuating member O<11> of which has a screw-driver slot for adjustment purposes and carries a dial O<12> movable with respect to a fixed index O<13> on a plate J4. This adjustment determines the rate of the slow return or compensating movement. The rod AB carries a transverse eccentrically adjustable pin AB<3> engaging one side of a lever ABC pivoted at GH<11>. The other side of this lever engages a thrust pin C<9> contacting a spring-biassed lever C<5> to which the floating lever C<4> is pivoted at C<6>. The point of action of the pin C<9> is adjustable to determine the extent of the follow-up movement. The pin C<9> is carried on an arm C<50> pivoted to a rack C<52> reciprocated vertically by a pinion C<54> carried on an adjustable shaft C<55>. The shaft C<55> which carries a dial C<60> is movable with respect to a further index C<62> on the plate J<4>. In a modified adjusting arrangement, the arm C<50> is pivoted on an arm projecting from a semicircular dial plate. The plate J<4> has apertures for the shafts O<11>, C<55> and windows J5, J<6> adjacent the indices O<13>, O<62> respectively. A pen arm B<9> connected by a stirrup B<7> to the lever B<4> records the changes in the controlling condition (temperature) on a continuously rotated chart J<1> in a housing J which encases the flapper D, its operating mechanism and the bellows devices GH<2>, GH<4>. The control point is adjustable by means of a lever C carrying the fulcrum C<2> and having a stirrup CI<3> which carries a pointer CI<4> and is connected by a link CI<2> to a shaft CI adjustable by means of a knob CI<6> within the housing J or by means of a shaft CI<8> passing through the hinged cover J<3> and engaging a kerf in the knob CI<6>. The capillary tube F<1>, Fig. 1, is carried in a hollow plug FA the inner end of which forms a valve FA<4> for byepassing the capillary restriction so as to permit of manual control of the pressure in the chamber F<4> and hence of the entire apparatus after the flapper D has been withdrawn so far from the nozzle E by adjustment of the shaft CI as to have no effect thereon. The plug FA has a filter FA<3> and an inlet FA<2>. Pressure gauges FA<7>, FA<8> indicating respectively the control pressure in the chamber F<10> and the supply pressure at F<2> are mounted with the plug FA and the relay valve mechanism in an extension of the housing J. Where a reverse movement of the valve a is desired upon a change of temperature, the link C<3> may be connected to the floating lever C<4> at C<31>. The symmetrical arrangement of the bellows G<2> GA, HA, H<2> minimizes the effect of atmospheric temperature changes.