The measuring part of the metal tube float flowmeter is composed of a conical tube with large upper and small lower. There is a metal float that can move up and down in the conical tube. When the measuring medium flows from the bottom to the top, the metal float will be pushed up. With the increase of the rising height of the metal float, the area through which the fluid passes will increase and the medium flow will increase. When the rising medium flow reaches a balance with the rotor weight and the upper and lower pressures, the stable balance will be at a certain value. Because the metal float is a moving magnetic body, the current value is proportionally coupled to the local indicator, and the analog output shows the value, and the flow value is obtained. This value is converted into a DC (4-20) MA signal and sent to the DCS operation station in the control room for display
Quickly judge the fault of metal float flowmeter
During the maintenance of metal tube rotameter, the common fault phenomenon of Zui is that the instrument is stuck and cannot display the actual flow. According to the structural principle of metal float flowmeter, the troubleshooting methods are as follows:
1) remote display fault
During on-site maintenance and repair of metal float flowmeter, it is often seen that the flow indication is unchanged and fixed at a certain value. At this time, * analyze whether the display meter circuit components are faulty, whether the flowmeter float is stuck, whether the transmission signal line is faulty, or whether the DCS control room is faulty. The quick judgment method is to loosen the fixing screws of the local remote transmission display part and the rotor part, move the display part to change the mutual position between it and the rotor part, and simulate the state of the float during dynamic flow. At this time, the metal float is fixed. According to the magnetic principle of the float, the follow-up magnetic steel in the display is coupled with the float. If the float is stuck, the pointer of the moving display part can change the display normally, which proves that the display part is normal. If the pointer cannot be changed, find the fault of remote display and signal power supply. The fault causes are as follows:
1.1 pointer card
(1) Vibration, when other equipment or instrument are overhauled, the pointer of the instrument is deformed and loosened, so that the pointer deformation cannot reflect the actual flow value. The treatment method is: replace the installation and adjustment with the display meter of the same model;
(2) The glass panel of the metal rotameter is damaged and the pointer is jammed. The treatment method is: disassemble the display meter and replace the glass panel.
1.2 pointer jitter
(1) The pointer of metal float flowmeter will slightly fluctuate due to the fluctuation of pipeline and medium;
(2) The pipeline and medium fluctuate slightly due to unstable operating pressure; For the above faults, please contact the control room to find out the operation reasons, adjust the process parameters to stabilize the pressure, temperature and flow, increase the damping of the metal float flowmeter, and improve the process environment to stabilize the flowmeter.
1.3 signal power failure
(1) Signal amplification and conversion components are damaged;
(2) Screw looseness and line transmission failure;
(3) DCS control station wiring terminal fault;
(4) Control station I / O module fault. The troubleshooting method is to measure the voltage DC (1-5) V at the rear terminal of the control station panel in the control room with the “split method”, analyze and determine whether it is a field fault or a control room fault. The high fault rate is due to the loose terminal screws, and the fastening screw fault can be eliminated. If the fault cannot be eliminated, you can find the fault of the DCS measurement module according to the terminal wire number, find the fault indicator of the module, and see whether there is a fault. You can also replace the measurement module of the same model with the “replacement method” to see whether the display is normal.
Maintenance and reconstruction of metal tube float flowmeter
(2) float fault
(1) During the start-up and production of the new project, due to improper operation of the metal float flowmeter, the stop valves at the front and rear of the flowmeter were quickly opened, which caused the float to rush up rapidly and the stopper was deformed and stuck;
(2) The float is deformed and not concentric due to various reasons during operation. Troubleshooting: remove the metal float flowmeter, remove the snap ring with pointed nose pliers, remove and take out the metal float, remember the direction of the metal float, and adjust the float and deformation parts to make them concentric with the upper and lower parts. Reassemble and install, push the float by hand or shake it up and down, and observe whether it can move freely and normally. When installed on the pipeline, the sealing gasket of the same size shall be replaced. The sealing gasket shall meet the pressure requirements of the pipeline and the material of the sealing gasket shall meet the process medium parameters. The vertical installation shall not be inclined. When the upper screw is fixed, the diagonal shall be “tight”, and the sealing gasket shall be uniformly stressed without leakage. The screws shall not be fixed too tightly to prevent the gasket from being crushed and damaged to prevent leakage. The float failure frequency Zui of metal float flowmeter is high. When the flow display of the operation station is abnormal, first check whether the rotor of the on-site metal float flowmeter is stuck. Eliminate the fault that is not the remote display part. The simple and effective method is to knock the vibration float with explosion-proof tools. Because of the magnetic adsorption of the rotor, there are many metal particles attached to it, causing the rotor to move up and down and get stuck. After knocking and vibration, part of the particles and dregs will flow out of the flowmeter along with the medium to make the metal tube float flowmeter work normally. When knocking can not eliminate the fault, the flowmeter can only be disassembled, the float can be cleaned, and it can operate normally after correct installation. Some of the metal float flowmeters in our factory are used to measure the colloidal liquid. The colloid itself has a certain viscosity. The plastic float and the plastic lined metal float flow meter are used to solve the problem of adsorbing metal dregs during the use of the plastic, which has an anti-corrosion effect. However, the relative cross-sectional area of the plastic float rod increases, and new problems appear in the operation and maintenance process. When the flow Zui is large, the top of the rotor rod will be sucked. The problem can be solved only by disassembling and reinstalling. The reason why the top is adsorbed is that the adsorption of engineering plastic is greater than that of metal. The area between the top of the plastic float rod and the plastic stopper is expanded, and the measuring medium has a certain viscosity. Theoretical formula of adsorption force: F = 10-2 (101-p) s, f is the size of adsorption force and S is the area of suction cup. It is concluded from this formula that reducing the top area of the float or destroying the top adsorption structure can solve the problem.
Reconstruction of flowmeter
Modification: slotting the top of the rotor rod to reduce the contact area. Because the hardness of the plastic material is limited, too much modification will make the flowmeter float unable to work normally. Use an iron saw to saw a cross groove on the top of the plastic material float rod, with a depth of about 2mm. The rotor cannot be absorbed when it is against the upper part. After the modification of the metal float flowmeter of our factory, the fault is eliminated. There are various problems in the use of the metal float flowmeter in our factory, which increases the maintenance of the instrument. The reasons are as follows:
(1) In order to facilitate instrument maintenance and prevent metal and other dregs from entering the instrument during initial startup after installation and maintenance, bypass pipeline and bypass valve shall be installed;
(2) Prevent solid impurities from entering the instrument during operation and install a filter;
(3) In order to ensure the stable operation of the flowmeter, the flow gas flowmeter is equipped with a damper. In the process of instrument maintenance and repair, it is necessary to think calmly, constantly summarize experience, think clearly, draw inferences from one instance, and understand the working principle of the instrument, so as to ensure the smooth operation of the production unit.
Post time: 24-08-22