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A pressure gauge is a measuring instrument used to determine the pressure of the medium inside pressure vessels. There are various types of pressure gauges, including those based on liquid columns, elastic elements, pistons, and electrical principles. Most pressure vessels use single-bellows pressure gauges of the elastic-element type. For pressure gauges installed on pressure vessels, the maximum reading on the dial should be 1.5 to 3 times the vessel’s highest operating pressure; 2 times being the optimal value. The larger the range of the pressure gauge, the greater the allowable error and visual distortion. When selecting a pressure gauge, it is also necessary to consider the vessel’s pressure rating and operational requirements. According to these requirements, low-pressure vessels should have pressure gauges with a rating of at least 2.5; medium- and high-pressure vessels should use gauges with a rating of at least 1.5. To enable operators to read the pressure values clearly and accurately, the diameter of the gauge dial should not be too small. In general, the dial diameter should be no less than 100 mm. If the pressure gauge is located far from the point of observation, the dial diameter should be increased; when the distance exceeds 2 meters, it should be at least 150 mm, and when it exceeds 5 meters, it should be no less than 250 mm. Pressure gauges for ultra-high-pressure vessels should have a dial diameter of at least 150 mm. When installing a pressure gauge, it should be placed in a location where it is easily visible to operators, with adequate lighting. It is also important to protect it from radiant heat, low temperatures, and vibrations. Pressure gauges installed at heights should be tilted slightly forward, but the tilt angle should not exceed 30°. The connections of the pressure gauge should be directly attached to the vessel itself. To facilitate the replacement and calibration of the pressure gauge, a three-way valve should be installed between the gauge and the vessel. This valve should be mounted on a vertical pipe section and should have an indicator to help with identification and replacement. In steam vessels, a trap should be installed between the pressure gauge and the vessel. For vessels containing high-temperature, highly corrosive, or condensable media, an isolation buffer device should be used between the pressure gauge and the vessel. Pressure gauges in use should have a warning line marked on their dials according to the vessel’s highest operating pressure; however, this marking should not be made on the dial glass, as this could cause misunderstandings among operators and lead to accidents. Pressure gauges that have not been inspected and certified, or those without seals, must not be installed or used. Pressure gauges should be kept clean, with clear and transparent dial glass, so that the pressure values indicated by the pointers can be seen clearly. The connections of the pressure gauge should be cleaned regularly. If, during operation, the pressure gauge shows incorrect readings, unclear markings, broken dial glass, or if the pointer does not return to zero after pressure release, or if the seal is damaged, it should be corrected or replaced immediately. The maintenance and calibration of pressure gauges must comply with the relevant regulations set by the metrology authorities. Pressure gauges should have calibration marks indicating the date of the next calibration or the valid period for calibration. After calibration, pressure gauges should be sealed with a seal