Patent GB-671260-A (GB)
Title: Improvements in hydraulic control systems
IPC: F15B20/00
Filed: 1950-03-17
Abstract: 671,260. Hydraulic transmission of power. SOC. D'INVENTIONS AERONAUTIQUES ET MECANIQUES, S.I.A.M. March 17, 1950 [April 11, 1949], No. 6765/50. Class 69 (ii). In a hydraulic control system wherein a plurality of hydraulically operated units, such as jacks Va, Vb, are connected in parallel to normal main supply and exhaust conduits N', N<SP>2</SP>, with separate normal control valve means, such as a distributor Da for each unit, there is provided a separate emergency supply conduit S<SP>1</SP> with emergency connections therefrom in parallel with each unit, an emergency control valve means da and a protection box Pa for each unit, the supply of pressure liquid from the normal supply N<SP>1</SP>, N<SP>2</SP>, to the normal control means Da being taken through the protection box Pa, and a piston controlled isolating valve 12 being provided therein with the piston subjected to pressure from the emergency valve means da. When the emergency control is brought into operation, the isolating valve 12 serves, whenever its piston is actuated by the emergency pressure, to isolate the supply line 14 connecting the protection box Pa to the normal valve means Da from normal pressure and connect the line 14 to normal exhaust. The jack Va is either fed from conduits N<SP>1</SP>, N<SP>2</SP> for normal operation or S<SP>1</SP>, N<SP>2</SP> for emergency operation and in order to normally retract the jack the handle Ma of the distributor Da, comprising four separate but interconnected valves 1, 2, 3, 4, is moved to the dotted-line position so that pressure liquid from conduit N' is led to the jack through a conduit a', holding valve 7, isolating valve 12, relief valve 8, line 14, distributor valve 2 and a conduit 15, the exhaust from the jack Va, flowing to conduit N<SP>2</SP> through a conduit 16, distributor valve 4 and a conduit a<SP>2</SP>. The jack is normally extended by moving the handle Ma to the full-line position. In order to extend the jack Va in an emergency the handle Ma of valve means da comprising two separate but interconnected valves 5, 6, is moved to the dotted-line position so that pressure liquid from conduit S<SP>1</SP> flows past valve 5 into conduits 18 and 19 and operates a plunger valve 17 before entering the jack, the exhaust escaping by conduit 15 and depending upon the position of handle Ma either valve 1 and conduit a<SP>2</SP> to exhaust N' or valve 2, line 14, orifices in relief valve 8, the opening 10 in a piston 9 of the protection box Pa and conduits a<SP>2</SP> and N<SP>2</SP>. The exhaust can only pass through the protection box due to pressure from conduit 18 in a conduit 13 acting upon the top of a piston 9<SP>1</SP> thereby moving downwardly the piston assembly 9, 9' so that relief valve 8 seats on a shoulder 21 ; downward movement of the piston assembly also closes the isolating valve 12. During normal operation the holding valve 7 is opened by the pressure in conduit N<SP>1</SP> so that should for any reason a loss of pressure occur in the normal supply N<SP>1</SP>, N<SP>2</SP> the valve closes and prevents operation of the jack from the normal pressure source. If an overpressure occurs it acts upon the piston 9 and thereby opens the pressure line to exhaust through the relief valve orifices and the valve controlled opening 10. Where a number of jacks are connected to the same supply conduits it is possible to operate one or more from the emergency supply whilst the remainder operate from the normal supply. In parallel with the normal and emergency supply conduits is another jack Vb the operation of which differs from jack Va only in that the emergency distributor comprises four valves whilst a plunger valve 26 is provided at each inlet to the jack Vb so that it may be both extended and retracted by the emergency supply. No outflow from the jacks takes place into conduit S' which is merely provided to exhaust conduits 13, 18 and 19 to allow operation of the jacks from the normal supply N<SP>1</SP> and N<SP>2</SP>.