GB892056A - Improvements in or relating to pneumatic pressure output relays - Google Patents

Abstract

892,056. Fluid-pressure servomotor-control systems. BAILEY METERS & CONTROLS Ltd. April 14, 1958 [April 12, 1957], No. 11870/58. Class 135. In a process controller having a nozzlebaffle pair and an associated negative feedback bellows or diaphragm the nozzle back pressure is not transmitted directly to the bellows or diaphragm but via a relay having proportional plus integral action. In the first example, Fig. 1, the controller 1 is responsive to changes in flow in a line 3 and adjusts the diaphragm operated regulating valve 6 in line 7. The pressure drop across the orifice 2 is reflected by the diaphragm 12 which is connected via a link 21 and a sealing diaphragm 23 to a balance beam 22 which carries a baffle 24 which cooperates with a nozzle 25. The nozzle back pressure is transmitted to a relay 35 the output signal from which is fed to the diaphragmoperated valve 6 and to a feedback bellows 32 which acts on a beam 30 carried by springs 31 and abutting a settable nut 29 on a screwed rod 28 carried by the beam 22. The relay 35, Fig. 2, comprises a four part body 41-44 supporting three diaphragms 46, 47, 48, which define chambers 49-52 and which are rigidly connected by a member 45 loaded by a spring 53 in the chamber 52. The chamber 51 has an exhaust port. The chamber 52 is connected to the nozzle 25. A valve spindle 62 having two closure members 61, 63 is controlled by the member 45 to discharge air from the chamber 52 via the valve 61 or to admit air to the chamber 52 via the valve 63. The chamber 52 is connected via an orifice 70 to the positive feedback chamber 49 so introducing integral action. The pressure in the chamber 52 is reflected in the bellows 32, Fig. 1, and constitutes the relay output signal. In another example, Fig. 8, changes in a variable condition are transmitted via links 303, 301, and a screw 312 to a baffle 315. The nozzle back pressure is transmitted to a relay 310 which is similar to the relay 35 of the previous embodiment and the output signal from which is fed to the line 319 and to a feed back diaphragm 306 which acts on the lever 301. In another example, Fig. 9, a change in a variable pressure is detected by a Bourdon tube 401 which is connected via a link 402, a pointer 403, a link 404 to a lever 405 carrying a baffle 406 which co-operates with a nozzle 407. The nozzle back pressure is fed to a relay 413 the output signal from which is led to indicating and/or recording and/or regulating means and to a feedback bellows 410 which acts on a lever 408 carrying the nozzle 407 and connected by a link 411 to a pointer 412.