Glass rotor flowmeter knowledge questions and answers

　　Simply put, the fluid must form a typical velocity distribution (laminar velocity distribution and turbulent velocity distribution) in a circular pipe in order to use mature mathematical models for calculation and accurate measurement. However, this typical velocity distribution must be formed by fully developed in-pipe flow, that is, a sufficiently long straight pipe section. However, if the fluid flows through a flow blocker (elbow, tee, valve, etc.), the velocity distribution will be distorted and vortexes will be generated. In this case, the fluid will become a non-fully developed pipe flow, and the flow velocity in any section of the pipe is different and changes at any time. Only at the end of a very long straight pipe section or after the installation of a rectifier can the velocity distribution be restored to a fully developed pipe flow. This is the fundamental reason why many flow meters require a sufficiently long straight pipe section.

　　For metal tube rotor flowmeters, the Ministry of Machinery's standards stipulate that the front straight pipe section should be at least 10 times DN, measured from the upstream flange end face of the flowmeter, and the rear straight pipe section should be at least 5 times DN, measured from the downstream flange end face of the flowmeter. DN refers to the flowmeter diameter.

　　For glass rotor flowmeters, the Ministry of Machinery standards do not clearly specify the length of the front and rear straight pipe sections, but stipulate that if a flow control valve is to be installed, it must be installed 5-10 times DN downstream of the flowmeter, measured from the downstream flange end face of the flowmeter. DN refers to the flowmeter diameter.

Technical Parameters
Nominal    diameter DN  (   mm )     model  Range Measuring range Cone tube length (mm) Accuracy level Allowable measured fluid conditions Water, 20°C LZB/LZJ LZB-( )F LZJ-( )F Temperature(℃) Pressure(MPa) 4 LZB-4 LZB-4F 10:1 1～10L/h 1.6～16l/h 2.5～25L/h 16～160l/h 25～250L/h 40～400L/h 100 2.5 2.5;4 -20～+120 ≤1 6 LZJ-6 LZJ-6F 2.5～25L/h 4～40L/h 6～60L/h 40～400L/h 60～600L/h 100～1000L/h 2.5 2.5;4 10 LZJ-10 LZJ-10F 6～60L/h 10～100L/h 16～160L/h 100～1000L/h 160～1600L/h 250～2500L/h 160 15 LZB-15 LZB-15F 16～160L/h 25～250L/h 40～400L/h   0.25～2.5/h 0.4～4/h 0.6～6/h 350 2.5 ≤0.6 25 LZB-25 LZB-25F 40～400L/h 60～600L/h 100～1000L/h   1～10/h 1.6～16/h 2.5～25/h 1.5 40 LZB-40 LZB-40F 160～1600L/h 250～2500L/h 4～40 /h 6～60 /h 430 50 LZB-50 LZB-50F 0.4～4 /h 0.6～6 /h   10～100 /h 16～160 /h 450 80 LZB-80 LZB-80F 10:1 5:1 1～10/h 1.6～16/h 5～25/h   50～250/h 80～400/h 500   ≤0.4 100 LZB-100 LZB-100F 5:1 5～25/h 8～40/h 12～60/h   120～600 /h 200～1000 /h Note: The maximum measuring range of liquid flow can be expanded to 90/h according to user needs.
Installation Dimensions	(mm)
Nominal diameter DN model           size   Connection A B C D E M N 4 LZB-4 36 171 119 43.5   145 Ø14 hose 6 LZB-6 10 LZB-10 43 244 178 208 Ø16.5 15 LZB-15 Ø95 470 Ø65 Ø15 4-Ø14 _______ _______ Flange 25 LZB-25 Ø115 Ø85 Ø25 40 LZB-40 Ø145 570 Ø110 Ø40 4-Ø18 50 LZB-50 Ø160 Ø125 Ø50 80 LZB-80 Ø185 660 Ø150 Ø80 100 LZB-100 Ø205 Ø170 Ø100

 

　    Glass rotor flowmeter is an instantaneous flow measurement instrument that is simple to use, easy to read, and widely used. In the field of environmental protection equipment and instruments, the usage is as high as more than 30,000 units per year. Therefore, it is extremely important to choose and use this instrument well.

   1. Types and selection of glass flowmeters

   　 Glass rotor flowmeters can be divided into eight series according to their use and scope of application: ordinary type, ribbed vascular type, small flow and small shape type, corrosion-resistant type, laboratory type, insulation type, alarm type and high-pressure resistant type. According to the instrument series spectrum formulated by the country, no matter which series, it includes a total of 12 calibers from 1 mm to 100 mm, and the measurable flow range is: liquid (water) 0.1 ml/min ~ 40 cubic meters/hour, gas (air) 1 ml/min ~ 1000 cubic meters/hour. The glass rotor flowmeter used for environmental protection instruments generally has a caliber of no more than 10 mm, and the measured flow belongs to the small flow range.

   The selection of glass rotor flowmeter can be considered from the following aspects.

   1.  The object of measurement. That is, the type, pressure and chemical properties of the measured medium. For example, for liquid medium and gas medium, a corrosion-resistant flow meter should be selected for corrosive media.

   2.  Performance of the flow meter itself. Generally speaking, if the price does not change significantly after the above conditions are determined, it is preferred to use a flow meter with a needle valve placed on the top; a flow meter with a larger flow hole, a direct flow scale; a simple structure; a flow meter with a smaller external size, etc. If the flow range is small, a ball float type can be selected because it is stable during measurement, not easy to accumulate dust, has high accuracy, and good interchangeability.

   3.  Choose based on price. Generally speaking, the higher the accuracy, the higher the price. The accuracy level of the instrument should be selected according to the measurement purpose. For example, if you only need to control the flow rate of the measuring medium, and after trial operation and adjustment, you need to keep this flow rate stable, then accuracy is secondary.

   2. Scale Correction of Glass Rotor Meteorometer

    　The scale of the glass rotor flowmeter is obtained by calibration under the factory conditions using water and dry air, which are close to ideal fluids, as the medium. However, there are two situations where the scale value cannot be used directly at the site of the flowmeter: one is that the measuring medium is not water and air, and the other is that although the measuring medium is water and air, its state (temperature and pressure) is different from the scale state. In this way, when using the flowmeter, in order to obtain the correct measurement results, the problem of correcting the scale value arises. Therefore, solving the problem of glass rotor flowmeter scale correction is the key to using this instrument well.    

     Why are there certain straight pipe sections before and after the velocity flowmeter when it is installed? The velocity flowmeter is a flowmeter based on the principle of directly measuring the full flow velocity in a closed pipe. Although there are many types, their measurement principles are the same. The accuracy of the measured flow velocity is not only related to the accuracy of the flowmeter itself, but also to its installation position. The ideal installation position of the flowmeter is that the flow state of the upstream and downstream fluids is a single-phase stable flow, so that the influence of the local resistance pipes upstream and downstream of the flowmeter on the fluid flow state does not directly affect the measurement accuracy of the flowmeter.