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The main features of throttling differential pressure flowmeter

by:Sure     2021-08-10
The standard orifice structure of the most common throttling piece is easy to replicate, simple, firm, stable and reliable in performance, long in service life, and low in price. The throttling type has a very wide range of applications, and there is no other type of flowmeter that can be compared with it. All single-phase fluids, including liquid, gas, and steam can be measured, and some mixed-phase flows, such as gas-solid, gas-liquid, liquid-solid, etc., can also be used. The most common standard orifice structure of throttling parts is easy to replicate in general production processes. , Simple, firm, stable and reliable performance, long service life, low price.   The application range of the throttling type is extremely wide, and there is no other kind of flowmeter that can be compared with it. All single-phase fluids, including liquid, gas, and steam can be measured, and some mixed-phase flows, such as gas-solid, gas-liquid, liquid-solid, etc. can also be applied. Generally, the pipe diameter and working state (pressure, temperature) of the production process are all available. .  The detection parts and the differential pressure display instrument can be produced separately from different manufacturers, which is convenient for specialization to form scale economic production, and their combination is very flexible and convenient. The inspection parts, especially the standard type, are universally used all over the world and are recognized by the International Standards Organization. The experimental research on standard detection parts is international, and other flowmeters generally only rely on individual manufacturers or research groups, so the depth and breadth of their research are not the same. From the time point of view, the standard detection parts have not changed since they were determined by the International Organization for Standardization in the 1930s. The accumulation of research materials and production practices is extremely rich, and the scope of application it involves is not comparable to a type of flowmeter.   Because of the above reasons, the standard throttling type can be put into use without real flow calibration, and it is the only one among the flow meters.   At present, the throttling type and dynamic head type are the most used in various types. More than 20 varieties of throttling type have been developed, and there are still new varieties developed, and the more mature ones are developing towards the standard type. ISO has a special technical committee responsible for this work. The dynamic head type is represented by the average velocity tube flowmeter, which has developed rapidly in recent years. It is the main variety of the plug-in flowmeter, and its consumption is increasing rapidly.   Throttle type mainly has the following shortcomings:    1) The repeatability and accuracy of measurement are at a medium level among flow meters. Due to the intricate influence of many factors, the accuracy is difficult to improve.  2) The range is narrow. Because the instrument signal (differential pressure) and the flow rate are squared, the general range is only 3:1-4:1.  3) On-site installation requirements are relatively high. If a long straight pipe section (referring to orifice plate, nozzle) is required, it is generally difficult to meet.  4) The impulse pipeline between the detection part and the differential pressure display instrument is a weak link, which is prone to leakage, blockage, freezing and signal distortion.  5) Large pressure loss (referring to orifice plate, nozzle).   In order to make up for the above shortcomings, the following measures have been taken in instrument development in recent years.  1) Regarding the widening of the range    The expansion of the throttling type range shall start from two aspects: 1) the development of a linear orifice plate; 2) the use of a wide range differential pressure transmitter or multiple differential pressure transmitters. (2) Development of fixed-value throttling pieces The fixed-value throttling piece means to equip each kind of diameter measuring pipe with a limited number of throttling pieces. The β value (aperture) of the throttling piece is selected according to the priority number system. 3-5 kinds of β values u200bu200bare matched with the diameter. The application of fixed-value throttling parts has many advantages: changing the defect of the application of the throttling parts; the production method of the throttling parts is changed from small production operations to mass production; for the contoured throttling parts (such as nozzles, venturi tubes, etc.) ) Use special processing equipment to achieve mass production, reduce production costs, and create conditions for expanded use; bring convenience to users and so on. (3) The problem of pressure loss usually means that the detection parts are of orifice plates or nozzles. In fact, a variety of low pressure loss throttling parts have been developed, such as various flow tubes (Door tube, Rollos tube, etc.). General-purpose venturi tubes, etc.), they are not widely used because of their bulky structure and high price. For example, the use of fixed-value throttling parts can greatly reduce the production cost and create conditions for wide application.  (4)Integrated throttling type  The throttling device and the differential pressure transmitter are made into one, which saves the pressure pipeline, reduces the failure rate, improves the dynamic characteristics, and is convenient for installation and use. It is welcomed by users. Foreign applications have been quite common. According to statistics, Japan built more than 400 differential pressure flow meters in four factories from 1996 to 1997, and integrated direct installation meters accounted for about one third. (5) Problems with installation conditions The length of the necessary straight pipe section of the classic venturi is short (about 5D-10D). When there is no long straight pipe section, try to use this kind of throttling piece. It is made into a fixed value throttling piece, which can reduce the manufacturing cost. . In recent years, in order to solve the interference of the flow resistance, the applicable flow regulator has been studied. When the accuracy is high, the throttling device and the flow regulator are supplied together to ensure the accuracy of the measurement, but also increase the pressure loss and maintenance workload.
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