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Aviation History
1960
1960 - 1116.PDF
12 FLIGHT 22 JULY I960 TYPE AWE . 144/5 ELECTRO-HYDRAULIC SERVO VALVE This electro-hydraulic servo valve, developed by Armstrong Whitworth from their successful aircraft unit, can be used to control a wide range of hydraulic machinery and is particularly suited to process control systems. The valve utilizes hydraulic rather than electrical power amplifications and has a remarkably high power gain. A diaphragm, clamped around its periphery by two coil housings, is used to control the power — instead of the usual torquemotor — and the valve is therefore not susceptible to vibration effects. The valve — see diagram — consists of a main valve and a pilot valve. The main valve is supplied with pressure oil through ports A and B. When the spool is in the central position — as shown — the oil escapes through the tapered slots to the opposed jets C and D in the pilot valve and impinges on each side of the diaphragm. The two coils can be energised to attract the diaphragm towards one or other of the jets. If the signal to the right hand coil is the stronger, the diaphragm will flex to the right, restricting the flow from the right hand jet and thus increasing the pressure in that line. Similarly, the pressure in the left hand line is reduced. This pressure difference is transmitted to the main valve and causes the spool to move to the left until the resultant decrease in discharge area of the tapered slot at the right hand end of the spool and the increase in that at the left cause equilibrium to be restored. The displacement of the spool uncovers ports E and F, thus opening pressure and return lines to the hydraulic machinery. ARMSTRONG WHITWORTH EQUIPMENT HUCCLECOTE, GLOUCESTER TELE, GLO noii SIR W. G. ARMSTRONG WHITWORTH AIRCRAFT LTD., A MEMBER OF THE HAWKER SIDDELEY GROUP
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