Patent ID: 7290440

Claim:
A leak tester which detects leakage of gas from a measured object, the leak tester comprising: a source of a pressurized gas which supplies the pressurized gas; a first pipe through which the pressurized gas from the source flows; a second pipe which communicates with the first pipe and through which the pressurized gas flows, the second pipe being branched from the first pipe, communicating with the measured object, and allowing the pressurized gas to flow in the measured object; an on-off valve, which is interposed between the second pipe and the measured object, and stops flow of the pressurized gas into the second pipe in accordance with opening and closing action of the on-off valve, the on-off valve stopping the flow of the pressurized gas into the measured object when closed; a third pipe, which communicates with the second pipe, and which is branched from the second pipe and interposed between the measured object and the on-off valve; a differential pressure detecting section which is connected to the first pipe and the third pipe, and detects a pressure difference over a predetermined time between the pressure of the pressurized gas supplied to the first pipe, and the pressure of the pressurized gas supplied in the measured object, the pressure difference being detected when the on-off valve is closed, and the pressure of the pressurized gas supplied in the measured object being defined based on the pressure of the pressurized gas supplied to the third pipe; and a pressure adjusting mechanism which adjusts the pressure in the first pipe to make the pressure of the pressurized gas in the first pipe constant, the pressure adjusting mechanism comparing the pressure difference detected by the differential pressure detecting section to a threshold pressure difference to detect said leakage, the threshold pressure difference determined by taking into account leakage of gas from the leak tester and based on the volume of the measured object.