Advantages and Disadvantages of V-Cone Flow Meters

1. Advantages of V-cone flowmeter:

1. Wide range ratio

McCrometer, the earliest manufacturer of V-cones, conducted a series of tests and research and concluded that the signal-to-noise ratio of V-cones is much smaller than that of orifice plates. Due to the small signal-to-noise ratio, V-cones can accurately measure small flow rates even when the measured differential pressure is under small working conditions. Therefore, it is not necessary to increase the damping of the transmitter to improve the influence of signal noise like the orifice plate. Because of this, the range ratio of V-cones is much larger than that of orifice plates. Professor SNS Ingh of the Indian Institute of Technology conducted experiments using oil and water at different Reynolds numbers and concluded that within a certain measurement range, the outflow coefficient of V-cones is almost independent of the Reynolds number. The author has also participated in the calibration of hundreds of V-cone flowmeters. From the data, it can be seen that generally within the accuracy range of 1.0, using a single differential pressure transmitter, the range ratio of V-cones can reach 10..1.

2. Low straight pipe section requirements

The self-rectification function of the V-cone makes its straight pipe section requirement lower than that of the orifice plate. Professor SNS Ingh of the Indian Institute of Technology used oil and water respectively, and placed valves with different openings at different upstream locations for testing. The final conclusion is: If the upstream interference occurs 10D upstream of the V-cone flowmeter, or farther away, then this asymmetric velocity distribution will not affect the value of the discharge coefficient, and the discharge coefficient will remain at the same value obtained under ideal conditions; if the location of the upstream interference source is less than 10D (such as 5D) from the V-cone flowmeter, the maximum change in the discharge coefficient is 6%. It can be seen that as long as there is a 10D straight pipe section in front of the V-cone, no matter what kind of throttling device is in front, it will not affect its measurement. ISO-5167 stipulates that the straight pipe section requirements of the orifice plate vary greatly depending on the different throttling devices in front, and generally require at least 20D. As mentioned above, the gas outlet of the test separator generally adopts a 4" pipe. For the V-cone, only a 1m straight pipe section is needed in the front and a 0.5m straight pipe section is needed in the back.

3. Small pressure loss

Pressure loss is the irreversible pressure, which is one of the important indicators to be considered when selecting a flow meter. In today's society where energy is scarce and energy conservation and emission reduction are advocated, this parameter is particularly important. Since the edge shape of the V-cone determines the flow state of the fluid, the pressure loss of the fluid is much smaller than the pressure loss when using an orifice plate. In addition, due to the self-rectification function of the V-cone, there is no need to add a rectifier in front of it, while the orifice plate requires a longer straight pipe section to adjust the flow state of the fluid. The space on the offshore oil platform is small, and it is difficult to meet the requirements of the straight pipe section. It is often necessary to add a rectifier to ensure the flow state of the medium. However, the disadvantage of the high pressure loss of the rectifier is that it consumes more energy. Even if the rectifier is not considered, under the same power, the pressure loss of the V-cone is generally only 1/2~1/3 of the orifice plate.

4. High precision

Since the V-cone structure has no moving parts, the V-cone has good repeatability, generally less than 0.1%. Due to its wide range ratio, that is, its linearity is good, its accuracy is high. According to GB17167-2006. General Rules for the Equipment and Management of Energy Metering Instruments in Energy-consuming Units., the accuracy level requirements for flow meters used for energy measurement are: coal gas and natural gas are 2.0 levels. Therefore, in the gas measurement at the outlet of the test separator, within the range of 10..1, the overall error of the V-cone plus the differential pressure transmitter and the secondary meter will not be less than 1.5 levels, which fully meets the measurement requirements.

5. Good long-term performance

Because the contour of the cone restricts the flow of the medium, the fluid forms a boundary layer along the cone, which means that the edge of the cone is not easily worn by unclean fluid, so that the opening ratio remains unchanged, allowing the flow meter to maintain accuracy for a long time without calibration.

2. Disadvantages of V-cone flowmeter:

1. Calibration required

Orifice is the only flowmeter that can guarantee its measurement accuracy by ensuring the geometric dimensions. V-cone is a new type of flowmeter. Although many manufacturers and researchers have done a lot of experiments, there are limited national standards for V-cone flowmeters to date. In addition, due to confidentiality and restrictions, there is a lack of available literature on the structural design of V-cone flowmeters. Each manufacturer produces according to the enterprise standard, so it can be said that the products are mixed, and not every manufacturer's products are reliable. Due to insufficient test data, each V-cone flowmeter must be strictly calibrated before leaving the factory. This also increases its cost.

2. Higher price

The price of a V-cone flowmeter of the same specification is higher than that of an orifice flowmeter, but lower than that of a replaceable orifice flowmeter. The V-cone is sold at a higher price due to the large amount of materials used, complex processing, and high calibration costs. However, when considering the flowmeter, the initial purchase price and installation costs, the reliability of the instrument, long-term maintenance costs, and the maximum pressure loss are all factors that should be considered.

The overall evaluation is the basis for selecting the flowmeter. Only by comprehensively considering and weighing these important factors can a reasonable selection be made. As mentioned above, except for the initial purchase cost of the V-cone flowmeter being higher than that of the orifice flowmeter, the other costs should be the same as or lower than that of the orifice flowmeter. Especially in terms of the energy consumption required to compensate for pressure loss, the V-cone flowmeter is far superior to the orifice flowmeter. Therefore, in the long run, the comprehensive cost of using the V-cone flowmeter is lower than that of the orifice flowmeter. The purpose of using a replaceable orifice plate is to improve the range ratio of the orifice plate. But it is expensive. If the V-cone flowmeter is equipped with two transmitters with different ranges, the expansion of its range ratio is much greater than that of the replaceable orifice flowmeter, and its price is much lower than that of the replaceable orifice plate.

3. Low differential pressure

Since the outflow coefficient of the V-cone flowmeter is greater than that of the orifice flowmeter, the differential pressure value of the orifice plate is higher than that of the V-cone at the same flow rate. The transmitter of the orifice flowmeter generally uses a medium differential pressure gauge, while the V-cone flowmeter generally uses a low differential pressure gauge.