Patent GB-1299018-A (GB)
Title: Method of sequential leakage testing
IPC: G01M3/26
Filed: 1970-07-02
Abstract: 1299018 Testing fluid systems for leaks: measuring pressure electrically GENERAL MOTORS CORP 2 July 1970 [31 July 1969] 32083/70 Headings G1S and G1N Automatic test equipment for testing a fluid system such as a vehicle hydraulic brake system comprises a hydraulic test circuit, Fig.1, an adapter 54 having a probe 58 capable of being fastened to a vehicle master cylinder port 186 by a toggle clamp 62, a hydraulic leak meter 30 supplied with pressure fluid from a line 28 and which electrically detects fluid leakage from that system which includes an intensifier 27 and a valve and filter system supplied with brake fluid from a line 10 at 20-200 p.s.i., a pneumatic system supplied from a line 70 at 60-125 p.s.i. and including air filters and valves to operate the intensifier 27 to automatically increase the hydraulic pressure within the system, and an electrical control system which controls timers, relays, the automatic test cycle, and operates accept and reject circuits. Initially the brake system test pressure is timed to exist at 2000 p.s.i. to expand the system prior to test but this automatically reduces to 1600 p.s.i. which is the test pressure when the air-pressure in the intensifier itself reduces. During this period at 1600 p. s.i. any leakage is measured by the meter 30 which takes account of any continued pipe expansion, and the system is then automatically re-set for a further test sequence and disconnected. The electrical control Fig. 5a is energized by the operator closing the main A. C. switch 194 and a start switch 195 which energizes a relay 196 which energizes the coil 216 and a relay 198. After the cable 147 is connected to the brake warning switch 188 the relays 190, 192 are supplied with D. C. via a rectifier. The relays 190, 192 will be energized if the safety switch 188 is not grounded and thus allows switch button 150 when operated to energize relay 200 and de-energize the accept and reject circuits operated by the relay 198. Relay 200 operates solenoid valve 40, Fig. 1, to allow fluid into the vehicle brake system whilst also re-setting the coil 154 in the leak meter 30. A fast timer 202 set for 10 seconds is then energized to apply fluid at 2000 p.s.i. through solenoid valves 98, 136 and an intensifier 27 and a circuit of reject control relays 204, 206 and 208 are prepared, Fig.5b. Release of the button 150 re-energizes the relay 198 which activates the holding circuits of the air reject relay 204, relays 206, 208, 210 and an accept relay 212. When 202 times out valve 98 is closed to reduce the test pressure to 1600 p.s.i. and a second timer 220 is energized for 5 seconds to allow the pipe expansion to stabilize. The timer 220 then times out and energizes relay 222 and a third timer 224. Relay 222 energizes a 10 sec test timer 228 for the duration of the 1600 p.s.i. pressure test and de-energizes the valve 40 which remains closed for this time. At the same time a relay 209 is prepared to read the output of relay 242 should a leak occur. The  test fluid is applied to chamber 36, 48, Fig. 2, and the piston 50 is free to respond to any leak in the system. If the system is O.K. the timer 228 energizes accept control relay 212 which operates a punch card solenoid 230 and a valve 125 which opens the air circuit to atmosphere via muffler 127. Relays 234 and 200 are energized which reset the test portion of the circuit. Simultaneously the energizing of relay 212 energizes and opens valve 40 which allows fluid into the intensifier 27 thereby reducing test system pressure to 30 p.s.i. Upon completion of the 10 second period, timer 228 opens circuits to the punch card solenoid 230 and leaks the reject relay 210. The re-set timer 232 permits the intensifier plunger 124 to pull fluid out of the test system before valve 20 is opened thereby allowing full reduction in pressure before any make-up fluid is added to the system. When 232 times out valve 20 is energized to supply the make-up fluid. The operator then manually disconnects the brake cable 147 and removes the stamped card and the test adapter 54. In Fig.5b the leak detector includes a 6 volt A. C. supply to the coil 156 of the leak meter 30 and the position of piston 50 determines the voltage in coil 158  and gives a leak indication via a D.C. supply circuit 240 and an analog comparator relay 242 where the voltage of 158 is measured against a reference voltage determined by a potentiometer 246.