Patent GB-704237-A (GB)
Title: Improvements relating to hydraulic pressure systems
Inventor: HANCOCK KENNETH GEORGE
IPC: F15B21/0423
Filed: 1950-05-11
Abstract: 704,237. Hydraulic machines. ELECTROHYDRAULICS, Ltd. Aug. 10, 1951 [May 11, 1950], No. 11827/50. Class 69 (2). [Also in Group XXXIII] In a hydraulic system for operating one or more devices, e.g. aircraft undercarriages, which include at least one jack having a permanently open orifice in its piston, thermostatic means are provided by which the temperature of the liquid in at least a part of the system is controlled automatically so that liquid is circulated through this part of the system and through at least one of said permanently open orifices until a predetermined temperature is reached. The system includes a tank 1 from which a pump 2 supplies liquid through a filter 3 to a hydraulic accumulator 5 supplied with air from a valve 50 which also supplies a compressed air accumulator 52 for emergency operation of the undercarriage. To lower the undercarriage current is supplied to an electromagnetic relay valve 15 in a selector 13 thus closing a valve 17 and opening a valve 18 so that pressure liquid flows from the accumulator 5 through lines 6, 7 and 8 and valve 18 to move the piston 21 of the selector 13 against its spring 22, thereby opening a valve 23 and allowing pressure liquid to pass from a pipe 9 through the selector into pipes 29 and 31 to move the piston 41 of the main jack 40 to lower the undercarriage. Liquid also flows from pipe 29 into pipe 32 to act on a piston 44 against its spring 83 to release the up lock, and into a pipe 33 to move the piston 46 to release the down lock. To retract the undercarriage, current is supplied to the electromagnetic valve 16 of the selector 14 thus opening valve 20 and closing valve 19; liquid flows from pipes 6, 10 and 11 through valve 20 to move piston 25 to open valve 27 so that liquid from pipe 12 flows into pipes 34 and 35 to move piston 46 to release the down lock. Liquid from pipe 34 will also act on the piston 41 to retract the undercarriage. The force of the undercarriage jack overcomes the load of the spring 83 to allow the undercarriage to go into the up locked position. For emergency lowering of the undercarriage a selector 56 is depressed allowing compressed air from the accumulator 52 to flow through pipes 53, 54, and 57 to move a piston 59 in an automatic control valve 58 to close a valve 60 and open a valve 61 so that air from pipe 53 flows through pipes 55, 62 and 64 to move a floating piston 45 to move the piston 44 to release the up lock; air is also passing from the line 62 to act on a floating piston 42 to move the piston 41 to lower the undercarriage, and into a pipe 63 to act on a floating piston 48 to move the piston 46 to close the down lock. The thermostatic means comprise thermocouples (not shown) in the hydraulic system so that at a predetermined temperature an electric current automatically actuates the intermittently operated pump if such a pump is used in the system, or if the pump is continuously operated, actuates the electromagnetic valves of the selectors. in both cases the last preceding operation of the system being repeated, e.g. if the last operation was " undercarriage up " liquid will be circulated for the up position. This circulation continues through the permanently open orifices 82, 85, 87 in the pistons till the heating up or cooling down through the circulation of the liquid reaches a predetermined temperature.