With the increasing modernization of industry and the socialization of municipal construction, the caliber of pipelines used by industry, municipal administration, and energy has gradually increased. The use of throttling devices (such as orifice plates and venturi tubes) not only has excessive pressure loss, but also has a large and bulky structure. The recent emergence of ultrasonic flowmeters is too expensive. In the past two or three decades, plug-in flowmeters have attracted people's attention and selection due to their simple structure, light weight, easy installation and maintenance, low pressure loss, and low price. Its characteristic is to estimate the flow rate based on measuring only one (or several points) of the flow velocity in the pipeline. Although simple, it has the disadvantage of being difficult to improve the accuracy. In the current market economy, logistics generally require economic accounting. For this reason, it is necessary to inquire whether the accuracy can reach ± 1% claimed by many manufacturers under actual application conditions.
的种类与特点 I. Types and characteristics of plug-in vortex flowmeters
1. Type: The classification of flow meters is generally based on principles such as throttling, vortex, electromagnetic, ultrasonic, etc. Most of these meters are installed on pipelines through flanges. The plug-in flow meter, as the name suggests, is a flow meter installed in the plug-in form, which measures the flow rate by measuring the flow rate at one point (or points) in the pipeline. It can be said that any instrument that can measure the flow rate can be a plug-in flow meter (this article only discusses a plug-in flow meter that measures a bit of flow rate). These flow meters are currently commonly used: 1) Pitot tube is a classic and relatively accurate flow meter. It was often used for on-site measurement decades ago. Due to its easy clogging and small output differential pressure, it is rarely used in industrial sites, but it is still often used for calibration. (2) Pitot-Venturi tube, also known as double horn tube or double venturi tube, is also based on the principle of pitot tube speed measurement, but the structure adopts acceleration and pressure reduction measures. At the same flow rate, it can be compared with pitot tube Obtain a larger differential pressure, and it is not easy to block, can withstand high temperatures, but the accuracy is not high. (3) Other flow meters, such as vortex, turbine, electromagnetic, etc. can reflect the size of the flow velocity. It can be made into a small measuring head, and the flow rate can be estimated by measuring the flow velocity at a point in the pipeline
优、缺点 2. Advantages and disadvantages of plug-in vortex flowmeters
(1) Simple structure, light weight and low manufacturing cost.
(2) The pressure loss is small, and the operating cost is low. It is an energy-saving instrument.
(3) A structure can be used for a variety of calibers (limited to the point speed type), which can reduce the number of user backups.
(4) Convenient for packaging, transportation, installation and maintenance.
(5) It can be installed and disassembled continuously, avoiding economic loss caused by interruption.
(6) The flow velocity distribution in the pipeline has too much influence on the measurement accuracy, and the straight pipe section is required to be as long as 30D ~ 50D.
(7) The situation on the site is complex, which has a great impact on its application and is difficult to standardize.
(8) The accuracy is difficult to improve, and generally can only reach ± (3 ~ 5%).
的安装技巧：1.插入式涡街流量计只能单向测量，安装时注意保证介质流量方向与流量计箭头所示方向一致。 Installation techniques for plug-in vortex flowmeters : 1. Plug-in vortex flowmeters can only measure in one direction. When installing, pay attention to ensure that the flow direction of the medium is consistent with the direction shown by the arrow on the flowmeter. 2. The best installation method of the plug-in vortex flowmeter is vertical installation, and the medium passes through the flowmeter from bottom to top. That is, the flow meter is installed on a vertical pipe, and the flow direction is from bottom to top. 3. For horizontal installation, the flowmeter must be installed in the high-pressure area of the entire system and the corresponding outlet pressure must be ensured. Do not install it at the highest point of the pipeline, because the highest point often has gas accumulation and the pipeline is not full. 4. When measuring high-temperature fluids, try to use a vertical installation method; if you have to install it horizontally, please install the transmitter part of the flowmeter vertically downward or horizontally to avoid excessive temperature; pay attention to the air flow at the installation location Or well ventilated. 5. Straight pipe section requirements: At least 15 times the pipe diameter in front of the flowmeter and 5 times the pipe diameter after the flowmeter are guaranteed. If there are interference sources such as elbows, indentations, and expansions in front of the flowmeter, you must ensure that the pipe diameter is 30-40 times in front of the flowmeter and 6 times in diameter after the flowmeter. The flow meter should be installed upstream of the regulating valve, pressure or temperature sensor. 6. Note that the diameter of the pipeline should be slightly larger than or equal to the internal diameter of the instrument during installation. 7. When using a sealing ring, note that the inner diameter of the sealing ring should be slightly larger than or equal to the inner diameter of the meter, and the center of the sealing ring is located in the center of the pipe.
Cable entry seal
When the instrument is electrically connected, the seal of the inlet hole must be paid attention to. The corresponding sealed interface (M20 × 1.5; 1/2 "NPT; G1 / 2") must be selected according to the meter cable entry model, and installed correctly and tightly. No sealing joint, or sloppy installation, can not achieve the sealing effect, is one of the most common reasons for instrument damage