GB1082736A - Leak testing method and apparatus - Google Patents

Abstract

1,082,736. Testing for leaks. AJEM LABORATORIES Inc. May 13, 1965 [June 16, 1964], No.20340/65. Heading G1N. A part is tested for leaks by forming a closed chamber in the part, supplying fluid under pressure to the chamber and to a standard chamber, segregating the chambers when pressures therein are equal, and generating a voltage proportional to any difference in pressure between the chambers after a predetermined time. Air is supplied to the test chamber under pressure and if the air in the chamber fails to reach the required pressure after a predetermined time due to a large leak the part is automatically rejected. If the required pressure is reached the pressure source is cut-off and the pressure in the chamber is reduced to a predetermined value. The test chamber is then connected to the standard chamber and sufficient time is allowed for the pressures to equalize. A valve in the connection between the chambers is then closed so that the test chamber connects with a chamber 27 on one side of a diaphragm 29 in a measuring instrument while the standard chamber connects with chamber 28. Electrodes 33, 34 are connected to a source 37 of highfrequency A. C., so that air between the electrodes is ionized. It is stated that any deflection of the diaphragm gives rise to a direct voltage proportional to the deflection, and this voltage is applied to meter 39. Light beams are directed through slit 49 in a shield plate on the meter and through slits in adjustable arms 47, 48, and impinge on two photo-cells (not shown), each connected in series with a relay coil. If the meter needle 40 is deflected sufficiently to block light passing to either photo-cell, the corresponding relay is deenergized, a normally lit "accept" lamp is extinguished and a "reject" lamp is lit. The part may also be automatically rejected. In the fluid-pressure system all the conduits and the standard chamber are preferably formed by passages in a solid mainfold block and the various valves are mounted directly on the block Figs. 6 to 10 (not shown) The operation of the apparatus is preferably controlled by a two-bank stepping switch, the first bank of which is connected to R. C. timing circuits controlling stepping of the switch, while the second bank is connected to circuits including silicon controlled rectifiers for controlling actuation of the pressure valves and the "accept" and "reject" lamps Fig. 12 (not shown). Faulty operation of the apparatus leading to a higher pressure in the test chamber than in the standard chamber causes the needle of meter 39 to move to the right and blocks light which normally falls on the second photo-cell. This also causes the "reject" lamp to light and the part to be rejected. Repeated rejection of parts thus indicates a fault. The parts under test may be on an intermittently moving conveyer belt.