Patent GB-1309171-A (GB)
Title: Liquid fuel systems
IPC: B64D37/32
Filed: 1970-06-24
Abstract: 1309171 Inerting system for aircraft fuel tanks PARKER-HANNIFIN CORP 24 June 1970 [14 Aug 1969] 30715/70 Heading A5A A system for avoiding the over-pressurisation of aircraft fuel tanks, and hence reducing fire or explosion risk, in general comprises a vent passage from the fuel tank to atmosphere containing a normally closed valve, means responsive to a pressure difference between the vent passage and atmosphere less than a predetermined minimum to transfer inert fluid from a tank thereof into the fuel tank, and means other than the said valve to prevent the said pressure difference from exceeding a predetermined maximum, irrespective of whether the vent passage connection to the fuel tank is open or closed. In one method of operation, (Figs. 1, 3), the inert fluid is introduced directly into the fuel tank and its pressure is controlled by a regulator, operative even if the vent system is non-functional. In another, (Fig. 5) the inert fluid is introduced into the fuel tank via the vent passage under the control of an on-off valve such that if the tank vents become clogged with fuel any excess inert gas pressure vents directly to atmosphere. Another method, (Fig. 7), combines the pressure regulator valve and indirect introduction of inert fluid. The pressurising system may be used in conjunction with a scrubbing system. The Fig. 1 system comprises fuel tank 24; nitrogen source 10; control unit 17; scrub unit 43; surge tank 57; vent pipe 58; and valve assembly 62; basically resembling that in Specification 1264841. Nitrogen supply line 15 leads to control unit 17 and passes in parallel with large capacity pressure control valve 18 and small capacity scrub valve 19. The outlets from 18, 19, lead to pressurisation and scrub manifolds 23, 21, and thence to fuel tank 24, manifold 23 communicating with constantly open nozzle 28. Scrub manifold 21 is part of the system for scrubbing dissolved O 2  from the fuel during flight disclosed in Specification 1264841. Spray bar 25 is connected to manifold 21 and also to valve 32 which in turn is connected to pumps P 1 , P 2  and to fuel feed line 37. Scrub sequencer unit 43 includes pressure differential-operated switch 44 connected between fuel tank 24 and reference tank 47. Fuel tank 24 communicates via ports 60, 61 with vent pipe 58 and surge tank 57, and via 57 with valve assembly 62 having scoop 63 open to atmosphere. Vent pipe 58 is of large capacity to equilibrate pressure in the vent passage and tank 24. Valve assembly 62 includes climb and dive valves 64, 65 sensing the vent passage/scoop pressure differential. As shown in Fig. 3, pressure control valve 18 has inlet and outlet chambers 80, 81 connected via port 82 and respectively connected to lines 15, 16. Member 83 has stem 84 connected to sealed bellows 85 and diaphragm 86, the two sides of 86 being exposed respectively to the scoop and vent passage pressures on valves 64, 65 via lines 87, 89. Spring 90 urges valve 83 open. Secondary valve member 93 is connected to sealed bellows 94 and diaphragm 95, the two sides of 95 being exposed to atmosphere via port 96 and chamber 81 via passage 97, and spring 98 urging valve 93 open. Relief valve 100 and bursting disc 101 (Fig. 1) are provided in case valve 18 fails properly to limit the N 2  discharge pressure into conduit 16.  Operation of the Fig. 1 and alternative systems is described in detail.