What are the positive displacement flow meters?

As a mechanical flow meter, the volumetric flow meter has the characteristics of no requirement for straight pipes and high measurement accuracy. It is widely used in the measurement of viscous media such as oil.

1. The twin-rotor flowmeter is the main type of volumetric flowmeter, with various forms and specifications, and can be used to measure various liquid and gas media.

2. Oval gear flowmeter, its flow part is mainly composed of two mutually meshing elliptical gears and their casing (metering chamber).

3. Pulley volume flowmeter, also known as Roots volume flowmeter. The working principle and process of this flowmeter are basically the same as those of the oval gear type. It also relies on the pressure difference between the inlet and outlet fluids to generate movement, and discharges four volumes of fluid in the "metering space" per rotation. The difference is that there are no teeth on the lumbar wheel, and they do not directly mesh with each other, but are transmitted through a transmission gear set installed outside the housing.

4. Scraper type: the fluid drives the scraper and rotor to rotate, and the scraper extends and retracts radially along a special trajectory. The distance between each two relative scraper end faces is a certain value. When the scraper rotates continuously, a fixed metering chamber is formed between two adjacent scrapers, the rotor, the inner cavity of the shell, and the upper and lower cover plates. Each time the rotor rotates one circle, four (or six) metering chamber volumes, i.e., the circulation volume, are discharged. According to whether the scraper is not in contact with the cavity wall, it can be divided into two types: elastic scraper and rigid scraper. The front end of the elastic scraper is in elastic contact with the cavity wall, which is suitable for measuring liquids containing impurities such as sand particles; the front end of the rigid scraper maintains a fixed and extremely small gap with the cavity wall, which is used for cleaning or liquids with fine powdery impurities. The structure of the rigid scraper can be divided into concave type (British AveryHardoll type) and cam type (American Smith type).

5. Rotary piston type. Insert the annular piston into the shell of the two-layer cylindrical cylinder, and the annular piston rotates in the shell with the flow of the liquid. The flow meter diameter is DN20~100mm, and the measurement accuracy is 0.5%R. It can be used for the measurement of oil products and food. 6. Reciprocating piston type. The piston reciprocates in the cylinder under the push of the fluid to measure the volume flow rate. Usually, the gas station's gas station is of this type, with a flow rate of 60L/min and a measurement accuracy of ± (0.15~0.3)%R.

6. Disc type. Also known as nutating flowmeter, the disc with a central ball rotates and swings up and down in the metering chamber to enter and discharge the liquid. Compared with other PDFs, it has poor accuracy and is more affected by viscosity. my country once produced it to measure petroleum products, but it is rarely used. In North America, it is more used as a domestic and industrial water meter.

7. The rotary drum type, also known as the wet gas meter, is used to measure the total amount of gas. The flow meter housing contains about half of the sealing liquid (water or oil), and the rotary drum is half immersed in the sealing liquid. The gas flows in to make it rotate, and its sealing form is leak-free. The range is wide at 20:1, and the performance is stable. Under careful operation, a high degree of ± (0.2~0.5)%R can be obtained. It is mostly used in laboratories and is often used as a value transfer meter or standard meter.

There are so many positive displacement flow meters, each with its own advantages and applied to different media measurement. Common positive displacement flow meters are oval gear flow meters, double rotor flow meters, lumbar flow meters and scraper flow meters. However, positive displacement flow meters are more expensive than general electronic meters, especially large-diameter ones are many times more expensive.