Precautions in vacuum equipment design:

1. Determine the total maximum allowable leakage rate of the vacuum equipment according to the process requirements of the equipment, and determine the maximum allowable leakage rate of each component based on this total leakage rate.

2.  Based on the maximum allowable leakage rate and other indicators of the equipment, the leak detection method to be used is preliminarily determined during the design phase, and it is used as one of the basic principles to guide debugging and acceptance.

3.  Based on the maximum allowable leakage rate index of the equipment or components, determine the sealing, connection method, and overall processing accuracy of the equipment, as well as which dynamic sealing form can meet the requirements. For example, the flange adopts metal sealing or rubber sealing.

4.  When designing the structural strength of containers, consideration should be given to the pressure resistance and structural strength that the tested piece should possess if using the pressure method for leak detection.

5.  When selecting structural materials for components, consider whether materials that may be corroded by working media and leakage gases have been used and may cause damage.

6.  When designing the structure, necessary backup interfaces for leak detection instruments should be left on the container or system for use in leak detection during equipment assembly and debugging. Especially for large and complex pipeline systems, segmented leak detection methods are usually required. Therefore, segmented isolation valves should be installed on the pipeline, and leak detection instrument interfaces should be reserved on each isolation section.

7.  When designing the structure of parts, try to avoid using design schemes that may interfere with leak detection work. For example, blind holes cannot be used for screw holes in vacuum chambers, as the gas in the remaining space inside the screw hole can only escape through the thread gap after installing the screw, resulting in virtual leakage. Thereby prolonging the system's pumping time and interfering with the normal operation of leak detection. The structure that should not appear in vacuum leak detection as shown in the figure.

8. Similarly, continuous double-sided welds and multi-layer sealing ring structures are not allowed in structural design, as this will create a "parasitic accumulation" in the middle where gas will form virtual leaks; When both inner and outer weld seams or sealing rings leak simultaneously, the "parasitic volume" causes the response time of the gas passing through the double-layer weld seam to be too long, making it impossible to detect leaks normally.

9. When designing welding structures, try to minimize the number of welds that cannot be leak tested after final assembly.

Leak detection in the manufacturing process of vacuum equipment

Is necessary during the processing stage of the equipment, and it is necessary to follow the processing technology (especially the welding process) to conduct leak detection on semi-finished components in a timely manner. For components that cannot be touched, leak checked, or repaired after manufacturing, the quality of the weld seam must be strictly inspected. Unqualified parts must be re welded, repaired, and re inspected in a timely manner. Only after meeting the requirements can the next process be carried out. Especially for the assembly, welding, and processing of large containers, leak detection during the intermediate process is crucial. If necessary, specialized leak detection tools (such as leak detection boxes, blind plates, etc.) should be designed and manufactured. For vacuum chambers using double-layer water-cooled jackets, it is best to first weld the inner chamber wall and perform leak testing to confirm that there are no leaks before welding the outer chamber wall. Similarly, for situations where there is insulation layer or other non removable structures on the outer side of the chamber wall, strict leak detection must be carried out on the chamber wall first before covering the outer structure. If conditions permit, all vacuum flanges and their connecting pipes (including vacuum chamber body flanges and chamber walls) should be processed by welding the flange surface. Flanges that are not processed after welding may meet sealing requirements during installation and commissioning, but during equipment use, factors such as heat and vibration may induce the release of welding stress, leading to flange deformation and decreased sealing performance. Strict adherence to vacuum operation hygiene and operating standards during the manufacturing process is also helpful in improving the airtightness of vacuum equipment and systems. After the welding groove is polished and formed, it needs to be cleaned and protected in a timely manner to improve the airtightness of the weld seam. The dynamic and static sealing surfaces of the processed components should have protective measures to prevent collisions and scratches during storage, handling, and assembly. When using welding corrugated pipes, metal ceramic or glass sealing parts, glass components and other vulnerable parts, careful operation should be carried out, especially to avoid damage caused by leakage after passing the pre inspection.

Leak detection steps during installation and commissioning of vacuum equipment

The installation and debugging phase is the main body of vacuum equipment or system leak detection work. If the airtightness of the equipment welds has been ensured through leak detection during the processing stage, then checking and ensuring the sealing of the connection parts during equipment installation and commissioning is the focus of leak detection work. Including key suspicious areas such as flange connections and dynamic seals between various pipelines and components. If leak detection is carried out on both the weld seam and the connection part at the same time, the workload and difficulty of leak detection will increase. It is best to use segmented leak detection for large and complex vacuum equipment. For each component installed, a leak detection should be conducted on its connecting parts and welds. After meeting the requirements, the next component can be installed. Because checking for leaks after fully assembling all components not only raises concerns about too many parts, but also the possibility of multiple leaks simultaneously, which poses great difficulties for overall leak detection. The leak detection steps during the installation and commissioning process of vacuum equipment are as follows:

1. Understand the structural composition and assembly process of the equipment to be inspected. Master the requirements of the equipment and identify the key suspicious areas that require leak detection.

2. Based on the requirements of the maximum allowable leakage rate and whether it is necessary to find the specific location of the leakage hole, and starting from the principles of economy, speed, and reliability, correctly select the leakage detection method or instrument, prepare the necessary auxiliary equipment for leakage detection, and formulate a practical and feasible leakage detection program.

3. Clean the inspected parts properly, remove welding slag and oil stains, clean them according to vacuum hygiene conditions, and dry them. For small devices with high requirements. After cleaning treatment, it can be baked in a vacuum drying oven. After cleaning treatment, it can not only prevent leakage holes from being blocked by dirt, oil, organic solutions, etc., but also protect the leak detection instrument.

4. Calibrate the leak detection sensitivity of the selected leak detection methods and equipment, and determine the leak detection time of the leak detection system.

5. If vacuum leak detection method is used, in order to improve the sensitivity of the instrument, the inspected part should be evacuated to a higher vacuum as much as possible.

6. Where possible, priority should be given to using more economical and on-site leak detection methods.

7. When using helium mass spectrometry leak detection equipment for leak detection, for the tested parts that do not require high leak detection or have large leaks, it is recommended to use helium gas with lower concentration for leak detection in the early stage of leak detection, and then perform leak detection for small leaks to save helium gas.

8. Timely repair and block the detected large leaks before conducting leak detection on small leaks.

9. Conduct a re inspection of the detected and repaired leaks to ensure that the leak detection results meet the requirements.