Knowledge Warmth**: Selection of pressure gauges

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(1) Selection based on the operating environment and the properties of the medium being measured. In harsh environments with high corrosion levels in the atmosphere, excessive dust, or the presence of liquids that can spray around, it is necessary to choose appropriate casing materials and protection ratings according to those environmental conditions. 1. Measurement of ordinary media: (1) For pressures ranging from -40 kPa to +40 kPa, a diaphragm pressure gauge is recommended. (2) When the pressure is above +40 kPa, a Bourdon tube pressure gauge or a diaphragm pressure gauge is generally used. 2. For dilute acids, acetic acid, and other generally corrosive media, acid-resistant pressure gauges or stainless steel diaphragm pressure gauges should be used. 3. For dilute acids and salts, acidic gases, heavy oils, and similar media that are highly corrosive, contain solid particles, or are viscous liquids, diaphragm pressure gauges should be used. The material of its diaphragm and separator must be selected based on the properties of the medium being measured. 4. For media such as those with crystallization, scarring, and high viscosity, flanged diaphragm pressure gauges should be used. 5. In environments with strong mechanical vibration, shock-resistant pressure gauges or marine pressure gauges should be used. 6. In flammable and explosive environments, where electrical contact signals are required, explosion-proof pressure controllers or explosion-proof electrical contact pressure gauges should be used. (II) Selection of accuracy class: For pressure gauges, diaphragm box pressure gauges, and diaphragm pressure gauges used for general measurement purposes, a class of 1.5 or 2.5 should be selected. 2. For precision measurement purposes, pressure gauges of class 0.4, 0.25, or 0.16 should be selected. (3) Selection of external dimensions: 1. For pressure gauges installed on pipes and equipment, the dial diameter is either 100 mm or 150 mm. 2. The pressure gauges installed on the instrument pneumatic pipelines and their auxiliary equipment have a dial diameter of less than 60 mm. 3. Pressure gauges installed in areas with low illumination, at high locations, or where it is difficult to read the indications, should have a dial diameter of 150 mm or 200 mm or more. (IV) Selection of measurement range: 1. When measuring a stable pressure, the normal operating pressure should be within 1/3 to 2/3 of the upper limit of the instrument’s measurement range. 2. When measuring pulsating pressures (such as those at the outlets of pumps, compressors, and fans), the normal operating pressure should be within 1/3 to 1/2 of the upper limit of the instrument’s measurement range. 3. When measuring high or medium pressures, the normal operating pressure should not exceed 1/2 of the upper limit of the instrument’s measurement range. (V) Selection of installation accessories: 1. When measuring water vapor or media with temperatures above 60°C, a condenser or siphon should be used. 2. When measuring easily liquefiable gases, if the pressure sampling point is above the instrument, a separator should be used. 3. When measuring dust-containing gases, a dust collector should be used. 4. When measuring pulsating pressure, a damper or buffer should be used. 5. When the operating temperature is close to or below the freezing point or solidification point of the medium being measured, insulation or heating measures should be taken.