[Q&A Question 235] 2017.08.23
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【Q&A Question 235】August 23, 2017: How should one proceed when installing a pressure gauge? The reference answer can be seen after replying; points for the correct answers are awarded based on identifying the key aspects. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) First, close the isolation valve on the tank, remove the pressure gauge. Coat the threads of the calibrated pressure gauge evenly with several layers of polytetrafluoroethylene, then tighten them using an adjustable wrench. After that, open the isolation valve. Scoring criteria: 2 points for incorrect answers; 3–8 points for incomplete answers; 10 points for correct answers accompanied by a detailed explanation; 15–20 points for correct answers with additional supplementary information. Please score according to these criteria. Note: If there are editing records after answering, only those who participated will be credited points. For continuous malicious spamming, 2 points will be deducted each time, with no upper limit. Pure numbers, pure emojis, or random letters that have nothing to do with the answer are all considered malicious spamming; points will start to be deducted after three warnings. 2017 Q&A Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (updates completed) http://bbs.hcbbs.com/thread-1597792-1-1.html Petrochemical Sector – “Creative Ideas for Energy Savings” Campaign (Phase 2 is in full swing) http://bbs.hcbbs.com/thread-1666758-1-1.html 2017 Coal Chemicals – “My Technical Upgrades” http://bbs.hcbbs.com/thread-1786290-1-1.html
1. The pressure gauge should be installed in a location that is easy to observe and access for maintenance. 2. The pressure gauge should be kept away from sources of vibration and high temperatures. 3. When measuring water vapor pressure, the pressure guide tube should be made in a U-shaped or ring shape to create a condensate seal that prevents high-temperature water vapor from affecting the elastic elements ； For corrosive substances, a neutral medium isolation tank should be used when introducing pressure. 4. When the pressure gauge is not at the same level as the pressure measurement point and the medium being measured is a liquid, it is necessary to take into account the effect of the liquid column height on the measurement value; in such cases, the reading indicated by the gauge must be reduced by the pressure corresponding to the liquid column between the center of the gauge and the pressure sampling point. 5. Sealing gaskets should be used at the connections of pressure gauges; for temperatures below 80°C and pressures up to 2 MPa, asbestos paper or aluminum sheets are used, while for higher temperatures and pressures, annealed copper or lead gaskets are employed. When measuring special media, special attention must be paid to safety; for example, when measuring oxygen pressure, it is necessary to prevent oils and organic compounds from coming into contact with oxygen ； When measuring acetylene pressure, it is strictly prohibited for copper to come into contact with it, etc.
First, close the isolation valve on the gauge, remove the pressure gauge, wrap several layers of PTFE evenly around the threads of the calibrated gauge, tighten them with an adjustable wrench, and then open the isolation valve.
The pressure gauge should be calibrated before installation, and it can be used only after passing the calibration. During installation, the pressure gauge should be fixed to a specially fabricated fitting, with gaskets used; it should not be secured by wrapping hemp thread or directly attached to the valve. The pressure gauge should be installed in a location that facilitates operation and maintenance. To ensure accurate measurement, the pressure sampling points must be representative. It should be selected on a straight pipe section with stable flow velocity, not at bends or dead ends in the pipeline; the pressure tapping tube generally should not extend into the equipment or pipelines.
(1) The pressure search table must be calibrated by the relevant metrology and calibration department of the labor bureau before installation; it can only be installed if it passes the calibration. Installed pressure gauges should be regularly recalibrated. It is not allowed to remove the lead seals privately for repairs, or to use pressure gauges that have not been calibrated beyond their expiration date. (2) The pressure gauge should be installed in a location where it is easy to view and clean, and it should be protected from vibration and high temperatures. Sufficient lighting should be available at the location where the pressure gauge is installed. (3) Pressure gauges should be installed in steam spaces such as the boiler drum or steam header; when installed on pipes, they should be placed in straight sections of the pipe. (4) Pressure gauges must not be installed directly on the boiler drum, steam distribution cylinder, or pipes; instead, a water storage pipe (elbow) should be connected, and a three-way stopcock should be installed between the elbow and the pressure gauge before connecting it to the equipment or pipes. The function of the bellows is to collect the condensate water in the steam, preventing it from entering the Bourdon tube directly and causing it to fail due to overheating. The three-way stopcock makes it easy to flush the pipeline and replace the pressure gauge.
For pressure gauges that have passed the inspection, wrap sealing tape around their threads in a counterclockwise direction. Hold the pressure gauge in place, install it on the adapter, turn it several turns tight, and then secure it using a 17mm fixing wrench and an adjustable wrench
1 The installation location shall meet the requirements of the installed state. 2. The front end of the installed radial pressure gauge should be equipped with a buffer ； For ease of inspection, a shut-off valve should be installed below the instrument ； When the medium is dirty or there is pulsating pressure, filters, buffers, and pressure stabilizing tanks can be used. 3. The distance between the installation site and the pressure measurement point should be as short as possible to ensure a proper seal and prevent any leaks.
1. The installation location shall meet the requirements of the installed state. 2. The front end of the installed radial pressure gauge should be equipped with a buffer ； For ease of inspection, a shut-off valve should be installed below the instrument ； When the medium is dirty or there is pulsating pressure, filters, buffers, and pressure stabilizing tanks can be used. 3. The distance between the installation location and the pressure measurement point should be as short as possible to ensure a perfect seal and prevent any leakage.
For isolation, first wrap sealing tape around it and tighten it with a wrench, then slowly open the isolation valve to check for any leaks
First, isolate the table and remove the pressure gauge. Wrap several layers of PTFE around the threads of the calibrated pressure gauge, then tighten it with a wrench. After that, open the isolation valve. Also, check whether there are any leaks after tightening; if there are leaks, address them
1. Select a pressure gauge with an appropriate pressure rating. 2. The pressure gauge must pass inspection before it can be used. 3. It must be installed vertically to facilitate observation. 4. A root valve and an annular pressure guide tube must be installed. 5. Use sealing tape and suitable gaskets (Teflon or copper gaskets) to ensure good sealing. 6. Introduce it into use gradually and carry out regular maintenance