Thread Content
Introduction: A pressure gauge is a device that uses atmospheric pressure as a reference to measure pressures that are either lower or higher than atmospheric pressure. On pressure vessels, a pressure gauge is a measuring instrument used to detect the pressure of the medium inside the vessel. There are many types of pressure gauges, which can be classified into four main categories: column-type, elastic-element type, piston-type, and electrical-type. Pressure vessels mostly use single-bellows pressure gauges with elastic elements. In industrial process control and technical measurement, pressure gauges are increasingly widely used. This is due to the high mechanical strength of the elastic sensing elements in mechanical pressure gauges, as well as the convenience of their production. The elastic sensing element in a mechanical pressure gauge undergoes elastic deformation as pressure changes. Mechanical pressure gauges use sensitive elements such as Bourdon tubes, diaphragms, bellows, and corrugated tubes, and are classified accordingly; the pressure they measure is generally considered relative pressure. Generally, atmospheric pressure is selected as the reference point. The elastic deformation of the elastic element under the action of medium pressure is amplified through the gear transmission mechanism of the pressure gauge, causing the gauge to display a relative value (higher or lower) with respect to atmospheric pressure. The pressure values within the measurement range are displayed by a pointer, and the indication range of the dial is typically set at 270°. Structural principle of stainless steel pressure gauges: A stainless steel pressure gauge consists of a pressure transmission system (including connectors, Bourdon tubes, flow-limiting screws, etc.), a gear transmission mechanism, an indication device (pointer and dial), and a casing (including the gauge body, cover, glass, etc.). The casing has a hermetic structure that effectively protects the internal components from environmental influences and contamination. For instruments filled with a liquid inside the enclosure (usually silicone oil or glycerin), this enables them to withstand severe vibrations in the operating environment and reduces the impact of fluctuations in medium pressure, as shown in the figure below. Image Classification: 1. Based on their measurement accuracy, pressure gauges can be divided into precision pressure gauges (GB/T 1227-2017) and ordinary pressure gauges (GB/T 1226-2017). The measurement accuracy grades of precision pressure gauges are 0.1, 0.16, 0.25, and 0.4 respectively ； The measurement accuracy grades of general pressure gauges are 1.0, 1.6, 2.5, and 4.0 respectively. 2. Pressure gauges are classified into general pressure gauges, absolute pressure gauges, and differential pressure gauges, depending on the reference for the pressure they indicate. A general pressure gauge is based on atmospheric pressure, an absolute pressure gauge is based on the zero level of absolute pressure, and a differential pressure gauge measures the difference between two pressures being measured. 3. Pressure gauges are classified into vacuum gauges, pressure-vacuum gauges, micro-pressure gauges, low-pressure gauges, medium-pressure gauges, and high-pressure gauges according to their measurement range. Vacuum gauges are used to measure pressure values below atmospheric pressure; gauge vacuum gauges are used to measure pressure values both below and above atmospheric pressure; micropressure gauges are used to measure pressure values below 60,000 Pa; low-pressure gauges are used to measure pressure values in the range of 0–6 MPa; medium-pressure gauges are used to measure pressure values in the range of 10–60 MPa; and high-pressure gauges are used to measure pressure values above 100 MPa. 4. Based on their display method, pressure gauges can be divided into pointer pressure gauges and digital pressure gauges. In addition, there are also pressure gauges for special purposes, such as: 1) The isolators used in diaphragm gauges (chemical seals) enable the separation of the medium to be measured from the gauge through a diaphragm, allowing for the measurement of pressure in highly corrosive, high-temperature, or crystallizing media, as shown in the figure below: Image 2) The casing of vibration-resistant pressure gauges is designed to be fully sealed, and the casing is filled with damping oil (silicone oil is commonly used nowadays); thanks to its damping effect, these gauges can be used in environments where there is vibration or fluctuations in medium pressure (load). 3) A pressure gauge equipped with an electrical contact control switch can perform signaling for alarms or control functions. 4) Pressure gauges equipped with remote transmission mechanisms can provide the electrical signals required in industrial engineering (such as resistance signals or standard direct current signals). Installation and Use: When installing a pressure gauge, it should be placed in a location where it is easily visible to the operator, with adequate lighting. Additionally, care must be taken to protect it from radiant heat, low temperatures, and vibrations. Pressure gauges installed at high positions should be tilted slightly forward, but the tilt angle should not exceed 30°. The pressure gauge connection should be directly connected to the container body. To facilitate the removal and replacement of the pressure gauge as well as its calibration, a three-way valve should be installed between the pressure gauge and the container. The stopcock should be installed on a vertical pipe section and equipped with an opening indicator for verification and replacement. A trap should be installed between the pressure gauge and the steam container. For containers holding high-temperature, highly corrosive, and condensable media, an isolation buffer device should be installed between the pressure gauge and the container. For pressure gauges in use, a warning red line should be marked on their dials according to the maximum operating pressure of the equipment; however, this marking should not be made on the dial glass, to avoid creating illusions for the operator due to the movement of the glass and thereby preventing accidents. Gauges that have not passed inspection and do not have lead seals shall not be installed or used. The pressure gauge should be kept clean, and the glass on its dial must be clear and transparent, so that the pressure value indicated by the pointer inside can be seen clearly. The connections of the pressure gauge should be flushed regularly. During the operation of the container, if issues such as a malfunctioning pressure gauge indicator, unclear markings, broken dial glass, a pointer that does not return to zero after pressure release, or damaged seals are detected, they should be corrected or replaced immediately. The maintenance and calibration of pressure gauges shall comply with the relevant regulations of the **metrology authorities. The pressure gauge should have calibration marks indicating the date of the next calibration or the validity period of the calibration. The calibrated pressure gauge should be sealed with a lead seal. The inspection cycle generally does not exceed six months (according to JJG 52-2013).