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I. Introduction

　　Valve is an important control component in fluid conveying system. It is widely used in petrochemical, thermal power, nuclear power and other industries. Accurate detection of valve leakage is of vital importance to industrial production. The pressure leak detection methods of valves in domestic and foreign patent documents mainly include: bubble method, soap bubble method, special tracer material method, water pressure method, ultrasonic method, pressure drop method, valve internal leakage temperature method.

　　 2. Several different valve leak detection methods

　　2.1 Bubble method

When using the bubble method for valve leak detection, fill the valve with a certain pressure of leaking gas and then put the valve into the liquid. The gas enters the surrounding liquid through the leak to form bubbles. The place where the bubble is formed is where the leak exists. . It is usually close by hand to observe whether bubbles are generated.

　　 In patent CN205785696, a camera is installed in the water tank 1 to realize remote observation of whether there are bubbles in the valve in the water tank 1. In the patent CN106052969A, when a bubble 25 is generated in the water tank liquid 27, the air detector 20 will output a signal of bubble generation, realizing the automatic detection of bubble generation.

　　2.2 Soap Bubble Method

　　 When using the soap bubble method for valve leak detection, fill the valve with a certain pressure of leaking gas and apply soap to the suspected leak. The place where the soap bubble is formed is the location where the leak exists. Usually manually observe whether bubbling and determine the size of the bubbling.

In patent CN105954015A, a camera is used to photograph the soapy water state of the valve 100 seal, and the control system 7 compares the received soapy water state image of the seal with the qualified soapy water state image stored in its memory to realize whether the valve leaks and the degree of valve leakage Automatic judgment.

　　2.3 Special tracer material method

When using the special tracer substance method for valve leak detection, fill the valve with a certain pressure of leaking fluid containing special tracer substances. When the special tracer substance escapes from the leak, use the detection device of the special tracer substance Find the location of the leak. The most common special tracer substance is helium, which is used in conjunction with a helium mass spectrometer leak detector for leak detection.

　　 When performing leak detection on valves for general use, a special tracer substance is mixed into the fluid controlled for leak detection. In the patent CN104977139A, an isotopic tracer material (such as carbon fourteen, tritium) is injected into the cold water circuit of the converter valve and mixed with the cold water liquid evenly, and the tracer material in the air around the converter valve is detected by a nuclear detection counter. In the patent CN107655636A, a colored liquid is injected into the valve housing, and the sealed valve housing is lowered below the water surface of the water tank to observe the color change of the water in the water tank and use color contrast to identify the leakage point. In the patent CN108279096A, the upper cavity of the valve body 31 is injected with iodine solution. If the sealing of the valve 30 is defective, the iodine solution will leak down to the glutinous rice paper 17 in the lower cavity and make the glutinous rice paper 17 appear blue. The color change of the glutinous rice paper 17 determines the sealing performance of the valve 30. In patent CN202720099A, the valve is filled with a mixture of hydrogen and nitrogen. When the valve leaks, the gas sensor detects the hydrogen and generates an electrical signal output and uploads it to the PLC. The PLC compares the measured leakage value with the standard value.

For some special purpose valves for leak detection, you can directly use the fluid controlled by it as a tracer. For example, in patent CN104913886A, freon valves use freon and halogen detectors for leak detection, and in patent CN107727324, natural gas valves use natural gas and natural gas In the patent CN204666317A, the gas valve uses methane and carbon monoxide in the fuel gas with a methane inspection probe and a carbon monoxide detection probe for leak detection. In the patent CN205138736A, the acid-base valve uses an acid hydrolysis solution and a PH display device for leak detection. .

　　2.4 Water pressure method

　　 When using the water pressure method for valve leak detection, fill the valve with water first, and then inject water with a pump to observe whether there is any water leakage around the valve. Normally, directly observe whether water leaks out manually.

In the patent CN205580687A, a water collection tank 4 is provided on the bottom side of the SVC valve block, a water-absorbing sponge 5 is embedded on the water collection tank 4, and a water-soluble fluorescent yellow powder is provided on the water-absorbing sponge 5. When the water leaks into the water collection tank 4, the water-absorbing sponge 5 Inhalation of the leaking water, the leaking water comes in contact with the water-soluble fluorescent yellow powder, and the obvious yellow-green fluorescence can be seen through ultraviolet radiation, so that the staff can clearly observe the water leakage with the naked eye in the distant and dark environment. In the patent CN107702866A, a water leakage detection module (short circuit detection) unit is composed of two metal guide pieces H201, H202 and a sensitivity adjustment resistor. When the two metal guide pieces open when no water leakage is detected, and when a water leakage occurs, both Two lead pieces are short-circuited and connected, and the corresponding I/O of the microcontroller changes from high to low. This falling edge will trigger the microcontroller to send out an alarm signal to warn the valve of leakage.

　　2.5 ultrasonic method

　　 When the ultrasonic method is used for valve leakage detection, the audible frequency part of the leakage sound is cut off, and only the ultrasonic part is amplified to detect the leakage. Usually, the staff directly use the ultrasonic detector to determine whether there is leakage according to whether the pointer of the detection instrument swings, or use frequency conversion technology to convert the ultrasonic signal into a signal that can be heard by the human ear.

In patent CN106033021A, the spectrum/amplitude display analysis software displays the amplitude spectrum of the acoustic signal of each frequency in the environment where the ultrasonic probe is located. By observing or monitoring whether the ultrasonic signal of a fixed frequency in the figure is significantly enhanced, or by judging whether it is fixed Whether the amplitude of the frequency ultrasonic signal exceeds the preset value, it can be safely, remotely, and on-line judged whether the steam safety valve has steam leakage.

　　2.6 pressure drop method

When using the pressure drop method for valve leakage detection, connect the compressor to the valve, and then press the pressure. When the pressure rises to a certain value, stop the pressure, close the valve at the same time, and leave it for a period of time. If the pressure drops sharply, the leakage rate can be judged If the pressure does not change much, it can be considered that the leakage rate is small or there is no leakage. Usually, the staff directly use the pressure gauge to determine whether there is leakage according to the change in the reading of the pressure gauge pointer.

In patent CN108332958 A, the high-pressure gas cylinder 5, the second pressure gauge 6, the second shut-off valve 7, the first pressure sensor 12, the test station 20, the second pressure sensor 13, and the fifth shut-off valve 14 are connected in sequence by pipelines. The pressure difference between the first pressure sensor 12 and the second pressure sensor 13 is used to judge the airtightness of the electromagnetic pneumatic shut-off valve on the test station 20.

　　2.7 Valve internal leakage temperature method

When the valve has a working fluid leakage, especially a high-temperature valve or a low-temperature valve, the heat emitted or absorbed by the working fluid will cause the temperature of the pipe wall to increase or decrease. If the valve leakage remains unchanged, the heat transfer process will tend to For stability, the heat dissipation or absorption and the tube wall temperature are maintained at a certain value. When using the valve internal leakage temperature method for valve leakage detection, temperature sensors are installed on the upstream and downstream of the valve to measure the ambient temperature around the valve, which is used as a characteristic parameter to detect whether the valve is internal leakage. The internal leakage of the valve is judged after instrument data analysis.

In the patent CN102478445A, by detecting the temperature of the outer wall of the pipe before the valve, the temperature of the outer wall of the pipe after the valve, and the ambient temperature, the heat dissipation heat Q of the pipe is calculated, thereby calculating the flow velocity and flow rate of the fluid in the pipe, and obtaining the working fluid leakage of the valve flow. In the patent CN102323013A, a temperature sensor is installed on the valve, and the information measured by the temperature sensor is compared with the temperature information measured by the temperature sensor when there is no leakage to determine whether the valve is leaking.

　　3, the end

Each valve leak detection method has different advantages and disadvantages. When leak detection is performed for a specific purpose valve, it needs to be based on the actual leak detection conditions and the leak detection requirements that need to be met, such as the length of time, cost, and operation. The method is easy, whether to determine the leakage point, whether to determine the leakage rate, whether to pollute the environment, etc., to choose the appropriate leak detection method