Experimental Characteristics of Scraper Flow Meters in Crude Oil Metering Verification

　　Experimental Characteristics of Scraper Flow Meters in Crude Oil Metering Verification

　　Working Principle of Scraper Flow Meters

　　The scraper-type flowmeter is a relatively common type of positive-displacement flowmeter. In this device, the flow measurement chamber contains two or three pairs of rotating scrapers. As the motor rotor spins, these scrapers roll axially within grooves machined into the cylindrical housing. Driven by the fluid pressure, the scrapers cause the stator to rotate as well. The scrapers continuously divide the flowing liquid into discrete volume segments, and a set of transmission gears, combined with a counting mechanism, accurately measures and records the total liquid output.

　　Factors Affecting Deviations in Scraper Flow Meters

　　1. Additional deviations introduced by the flowmeter itself

　　The physical properties of crude oil undergo certain changes as temperature and pressure vary. When using a scraper flowmeter for metering and verification, operational process parameters—such as ambient temperature, working pressure, and viscosity—can all influence the volume of crude oil being measured. Among these factors, temperature has the most significant impact on scraper flowmeter calibration. Even slight variations in ambient temperature can trigger a cascade of parameter changes, affecting the oil’s volume, density, viscosity, as well as the clearances between the flowmeter’s housing and its internal components. This, in turn, leads to fluctuations in leakage flow. For instance, when ambient temperature drops, paraffin and asphaltene deposits tend to adhere to the inner surfaces of the flowmeter housing and its internal parts, altering the effective volume of the metering chamber and directly compromising the accuracy of the flowmeter’s measurement. A scraper flowmeter operates by counting the number of times crude oil fills the metering chamber, thereby determining the total volume of oil being transported. However, due to the inherent gaps between the flowmeter rotor and the chamber walls, combined with manufacturing tolerances in both the rotor and chamber dimensions, some degree of media leakage is inevitable. Fortunately, these leaks typically remain within the design specifications, though they still contribute to the overall measurement error. The primary sources of this additional deviation include factors such as flow rate, fluid viscosity, ambient temperature, operating pressure, and the duration of use.

　　2. Deviations Caused by Damage to the Scraper Flowmeter Verification Room

　　Because crude oil often contains fine residual particles, these can cause friction between the motor rotor and the housing of volumetric flow meters. Over time, this friction gradually damages both the rotor and the housing, widening the gap between them and increasing internal leakage. As a result, measurement errors shift in a "negative" direction.

　　Scraper Flowmeter Characteristics

　　1. The measurement accuracy is high, with basic errors typically ranging from ±0.2% to ±0.5%, and can even reach ±0.1% under special requirements. Notably, the characteristics of scraper flowmeters are largely unaffected by changes in fluid conditions or significant limitations imposed by flow resistance.

　　2. The scraper flowmeter can measure liquids with lower viscosity, and changes in fluid viscosity have relatively little impact on the measurement range.

　　3. The rotary-type electronic counter measures the cumulative liquid flow without requiring an external power source, making it highly convenient to use. The electronic counter features dual displays for accumulated flow, one of which can be reset to zero, allowing customers to conveniently operate even in situations where continuous metrological verification is unavailable.

　　4. The rolling bearings are made from cemented carbide material, offering features such as wear resistance, corrosion protection, sand resistance, and stable performance.

　　5. Gear Differential Regulator: The stepless speed-regulating gear differential regulator is a unique, proprietary technology developed exclusively by Chinese manufacturers of scraper flow meters, offering convenient adjustment. When the measurement range of the scraper flow meter deviates from the calibrated reference value and needs adjustment, simply use a screwdriver to turn the adjustment rod directly—no need to replace any components—until the desired setting is achieved.