What is an elliptical gear flowmeter
Elliptical gear flowmeter is a precision instrument used to measure liquid flow rate. It is a direct reading cumulative instrument that measures the total flow rate of liquid flowing through the pipeline. The elliptical gear flowmeter can use two counting mechanisms: mechanical display head and electronic display head. The display head has the functions of displaying cumulative flow rate, instantaneous flow rate, and zero return, and can achieve on-site display and remote control.
It has many advantages such as a large range, low pressure loss, strong viscosity adaptability, ability to measure high temperature and high viscosity liquids, convenient calibration, and easy installation. It is a representative product of volumetric flow meters.
The LC series elliptical gear flowmeter is equipped with on-site pointer display and word wheel cumulative counting device, which can directly display the cumulative flow rate of liquid flowing through the pipeline. Especially suitable for measuring finished oil media. Widely used for flow measurement of non corrosive media in industrial sectors such as petroleum, chemical, synthetic fiber, transportation, commerce, food, medicine and health.
Product principle and structure
The elliptical gear flowmeter consists of a flow transmitter and a counting mechanism. The main part of the transmitter consists of a measuring chamber equipped with a pair of elliptical gear rotors and a sealed coupling. The counting mechanism includes components such as deceleration mechanism, precision adjustment mechanism, counter, and electric pulse transmitter.
The measuring room mainly consists of a pair of elliptical gears and a cover plate forming a crescent shaped cavity as the unit of measurement for flow rate. The elliptical gear rotates by the pressure difference between the inlet and outlet of the flowmeter, continuously measuring the liquid at the inlet through the crescent shaped cavity and delivering it to the outlet. The amount of liquid flowing through each rotation is four times that of the crescent shaped cavity in the figure. The total number of rotations of the elliptical gear and the speed of rotation are transmitted to the counting mechanism through a sealed coupling. The total amount of liquid passing through the pipeline can be determined by the pointer display and the accumulation of the character wheel. In the counting mechanism, a pulse transmitter can also be installed to form an elliptical gear flowmeter with transmission, which can be matched with our company’s electrical display instrument to achieve remote transmission (quantitative, cumulative, instantaneous, etc.) automatic.
Elliptical gear flowmeter
Advantages of elliptical gear flowmeter
*The caliber ranges from 10 to 250mm;
*There are multiple options for shell materials to choose from: aluminum, *stainless steel, and medium to high pressure stainless steel PPS、 Bronze, etc;
*There are various bearing materials to choose from: ceramic, bronze, Hastelloy, carbide PPS、 Stainless steel, etc;
*Material of shaft: 316 stainless steel;
*The materials for O-rings include VITON, fluororubber, stainless steel, and *Teflon for selection;
*The range ratio is 10:1, and the maximum can reach 50:1;
*The accuracy is two types: ± 0.2% and ± 0.5%, with a repeatability of ± 0.03%;
*During installation, the requirement for the straight pipe section is 5D+3D, and a filter needs to be installed;
*The viscosity can reach up to 1000 000CP;
*The pressure level can reach up to 640 bar;
*The maximum temperature resistance level can reach -10~450 ℃; (Insulation jacket type)
* Special flow meters can be customized according to customer requirements
*The electronic meter head can provide 4-20mA output, pulse output, 485 read protocol, and HART protocol.
*Error calculation and adjustment
7.1 The basic error of the flowmeter is calculated based on the measured values at each calibration flow point using the following formula: (volumetric method)
E=(Vmmdash;V)/ V×100%
Emdash; mdash; The flowmeter error (generally referring to cumulative error) is taken as two significant digits.
Vmmdash; mdash; The value measured by the flow meter (i.e. indication)
Vmdash; mdash; After correction, the measured value of the flow standard device (i.e. actual value)
According to the basic error calculation formula, when Vmgt; At V, the basic error of the flowmeter is a “+” value, indicating that the flowmeter is running fast.
In order to keep the flowmeter error within the basic error limit, error adjustment is often necessary. That is, by replacing a pair of adjusting gears (adjusting teeth) installed in the counter to change the mechanical transmission speed ratio, the reading of the flowmeter can be adjusted.
Error adjustment cannot change the flow characteristics of the flowmeter, only artificially placing its characteristic curve in a new coordinate system.
Generally speaking, within the specified (or actual) flow range, the basic error range of the large and small flow calibration points is not greater than the basic error limit of the specified accuracy, and the basic error of the flowmeter can be adjusted through error adjustment to make it qualified.
Used flow meters are generally first calibrated for errors using the original adjusting gear, and then adjusted for errors based on specific error conditions.
Error Adjustment Method for Elliptical Gear Flow Meter (Instructions for Using Error Adjustment Table)
The standard double-layer gear used in design is 38/35. If the flow meter runs too fast during inspection, a (+) error may occur, such as+1.02~+0.3. The double-layer gear 38/35 should be replaced with 41/38. At this point, the origin of the error curve will move from the zero position corresponding to the 38/35 gear to the position corresponding to the 41/38 gear at+0.63 (see table). This way, the error curve will be in the new coordinate system, and the error of the flow meter will be adjusted within the range of+0.39~-0.33 to meet the qualification requirements (see Figure 1).
2. In the use of flow meters, errors often vary due to different working conditions and changes, and may exceed the tolerance. As long as the error range does not exceed 1%, it can generally be adjusted to be qualified. For example, when the instrument error drops to -0.7~+0.2, and it is necessary to replace the double-layer gear, the first thing to consider is how many teeth the double-layer gear has. If it is a 41/38 gear, the corresponding error+0.63 of the gear should be taken as the zero position (i.e. coordinate origin). At this time, the 41/38 gear should be replaced with a 40/37 double-layer gear, and the error curve origin will move down from the zero position corresponding to the 41/38 gear to the position of the 40/37 gear+0.43, so that the error curve is in a new coordinate system.
Installation and use:
1. Before installation, the pipeline should be thoroughly cleaned and a filter should be installed in front of the flowmeter to prevent debris from entering the flowmeter. When the tested liquid contains gas, an air separator should be installed.
2. It should be noted that the elliptical gear shaft of the flowmeter must be installed in a horizontal position, that is, the dial must be perpendicular to the ground plane. The valves for regulating flow and starting and closing should be installed separately at the inlet and outlet ends of the flowmeter.
3. The arrow on the flowmeter housing should point in the same direction as the liquid flow in the installed pipeline.
4. The pipeline for continuous flow and the horizontal pipeline for installing flow meters should be equipped with bypass valves for regular cleaning and maintenance. Flow meters on vertical pipelines should be installed in bypass pipelines to prevent debris from falling into the instrument.
5. Under correct installation conditions, the elliptical gear flowmeter can rotate the counter 180 degrees as needed for easy reading; Or 90deg;
6. It is strictly prohibited to test flow meters with water.
7. When starting or stopping, the valve should be opened and closed slowly to prevent sudden impact and to prevent backflow.
8. When conducting maintenance, the back cover must not be disassembled to avoid accuracy changes during reassembly and affect accuracy.
