GB1355659A - Fluid pressure responsive apparatus - Google Patents

Abstract

1355659 Fluid-pressure servomotor systems WESTINGHOUSE BRAKE & SIGNAL CO Ltd 28 Sept 1971 [26 Oct 1970 2 April 1971 (2)] 50800/70 8507/71 and 8508/71 Heading G3P [Also in Division F2] Fluid-pressure-responsive apparatus for comparing first and second fluid pressures includes a fluid-tight vessel 4, Fig.1, divided into a first and second chamber 1, 2, respectively by a pressure responsive member 15, the first chamber having a first port 11 for a first input fluid-pressure signal and the second chamber having both a second port 12 for a second input fluid-pressure signal and a third port 13, the pressure-responsive member 15 comprising a flexible fluid-tight membrane with a surface deformable to itself to close the third port 13 when the requisite force difference exists across it, the third port 13 being vented through a restricted passage 3 to atmosphere, the fluid flow in this restricted passage depending on the degree of closure of port 13 by deformation of the membrane, such flow giving rise to a third (output) fluid-pressure signal indicative of the difference between the first and second pressures. As further shown in Fig.1, fluid-pressure conduit 5 may be a railway train brake pipe, the arrow indicating normal direction of flow. A restrictor 31, (e.g. the driver's brake valve) may be interposed between points 21 and 22 where the connections are made to chamber 1 and chamber 2 respectively, and a second restrictor 32 having similar flow characteristics to restrictor 31 but of much smaller size is interposed between point 22 and inlet 12. Initially, diaphragm 15 closes port 13, so pressure in chamber 2 builds upupto restrictor 32 until this pressure equals that at point 22. This pressure is greater than that at 21 (because of restrictor 31), so the diaphragm is displaced from port 13, and flow through restricted passage 3 begins. This rate of flow simulates that through conduit 5 and may be measured by a flow-meter or, as shown, a pressure gauge 47, calibrated in terms of flow in conduit 5; if restrictor 32 is changed for one of a different size, the scale on guage 47 is changed at the same time. Taking into account known leakage characteristics of brake pipe 5, gauge 47 could be calibrated, and include a movable pointer, so that an operator could determine whether or not the brake system of a freshly-assembled train was in order, and also determine during train operation whether the leakage had varied by an excessive amount. Fig. 2 (not shown) repeats the arrangement of Fig.1 but has added features. Thus, cut-off valves (6) and (7) are provided upstream of point 22 and between point 22 and inlet 12 respectively, the connection between 21 and 11 has a T-junction leading through a check valve (9) to a reservoir (8), and a further inlet (14) for chamber 2 is connected to a point between the check valve and the reservoir. In operation, if cocks (6) and (7) are left open, the apparatus may be used in the same way as that of Fig.1 to measure pressure or flow. If cocks (6), (7), are closed, conduit 5 having been charged with fluid previously, any leakage from conduit 5 will cause check valve (9) to close, whereupon reservoir (8) will feed chamber 2 via inlet (14), raising diaphragm 15 and causing flow through port 13 and restrictor 3. In fact, port 13 will be alternately opened and closed rapidly, but gauge 47 will register a steady value which represents the leakage rate from conduit 5. In Fig.4, provision is made to allow for non- linearity of the scale of pressure gauge 47. Conduit 5 is connected to the passage from port 13 to restriction 3 through a first valve 51 which reduces the pressure from conduit 5 to a fixed value which will be maintained over a range of fluid pressure levels in conduit 5, and through a constant-pressure-difference valve 52. One or both valves may be omitted (the connection from conduit 5 being retained) provided the scale is marked appropriately or arrangements made to adjust the zero. (The connection to 53 may be from a source other than conduit 5.) A spring 16, chosen in size to compensate at lower flow values supports diaphragm 15 to allow for the out-ofbalance force resulting from reduction of area of the diaphragm by port 13. Fig. 3 shows an arrangement to control a pressure in accordance with a reference pressure. The reference pressure is connected to port 11 of a device 10 (compare Fig. 1) and the pressure to be controlled is connected at 43 to the self-lapping controlled part 42 of a relay valve 40. The controlled pressure, at 44, is applied to the second input port 12 of device 10. The connection from third port 13 of device 10 to the closed-volume control port 41 of valve 40 exercises control by determining the position of exhaust tube 45 spanning both parts. Fig. 5 (not shown) is a cross-section of an embodiment suitable for manufacture.