GB1404991A - Fluidic control system - Google Patents

Abstract

1404991 Fluid-pressure servomotor systems PROCESS SYSTEMS Inc 11 May 1972 [12 May 1971 9 Aug 1971] 22245/72 Heading G3P [Also in Divisions F2 and G4] A fluid-pressure control system provides a pressure in a chamber that is the analog of a digital signal applied to digital valves coupling the chamber to a source of constant pressure or coupling the chamber to a receiver. In the former case the chamber is coupled to the receiver, and in the latter case to the source, via one or more orifices of constant cross-sectional area. The receiver may be the atmosphere. In one embodiment, Fig. 2, the valves 36-39 of the converter control the flow between an inlet manifold 34 and an outlet manifold 35 constituting the chamber referred to above. Each valve includes a needle assembly 45 spring urged towards seat 47. When coil 52 is energized the needle assembly 45 rises to allow fluid-flow. Each valve has a screw thread 50 so that, by rotating the valve when clamping ring 56 is released, the effective area of the orifice defined by seat 47 and the raised needle 45 is adjustable. Bleed ducts 64, 65 are provided as shown, duct 64 maintaining a required minimum pressure in manifold 35 when all the valves are closed, duct 65 setting an upper limit to the flow-rate. The pressure in manifold 35 may control a movable element of a valve forming part of a system monitored by a sensor, the sensor output being fed back to a device producing the digital signals controlling the valves. The ratio of the pressure in manifold 34 to that in manifold 35 is kept at about 2:1 (for air) which is larger than the critical pressure ratio. The ratio of the pressure in manifold 35 to atmospheric pressure is kept larger than 2:1. As a result there is sonic velocity air-flow through the valves, which isolates the manifolds from one another so that pressure changes in manifold 35 do not alter the mass flow-rate through the valves. To maintain the pressure ratio across the duct 65 it may be necessary to couple it to a vacuum chamber. In a second embodiment, Fig. 6, each electrically controlled valve 95 controls the flow between an inlet duct 81 and an outlet duct 82. A needle valve 97 permits adjustment of the flow-rate for each valve. The inlet and outlet ducts are connected by a bleed channel including needle valve 93. The outlet duct 82 has a bleed 88 to atmosphere.