What is the price of positive displacement flow meters?

Positive-displacement orifice plates are much more accurate than venturi orifice plates; they are often used for precise measurement of oil products. Their use is recommended. As for their price, it’s hard to say – given that the internal structure of positive-displacement devices is more complex than that of venturi orifice plates, they are likely to be slightly more expensive at the same level of accuracy

I have seen rotary vane flowmeters used to measure methanol; due to the high content of solid particles in methanol, clogging of the wheels often occurs, so caution is advised. Consider how many solid particles are present in your light diesel This post was last edited by wwxxss_1 on 2009-2-25 08:11]

Which flow meter to use depends on the medium, temperature, and accuracy requirements. Positive-displacement types have high precision and cost tens of thousands of dollars; they are not used unless high accuracy is required for measurement.

A mass flow meter can be used as well, right?

Yeah, the mass meter mentioned upstairs would work too, but compared to the flow meter mentioned by the original poster, which one is more expensive?

Positive displacement flow meters – Also known as fixed-displacement flow meters, or simply PD flow meters, they represent the category of flow meters with the highest accuracy. It uses mechanical measuring elements to continuously divide the fluid into individual, known volume portions, and measures the total volume of fluid by counting the number of times each volume portion is filled and emptied in the measuring chamber. 　　Positive displacement flow measurement involves using a fixed small volume to repeatedly measure the volume of fluid that passes through the flow meter. Therefore, an area within the positive displacement flow meter that constitutes a standard volume must be present; this area is commonly referred to as the flow meter’s “measurement space” or “measurement chamber.” This space is formed by the inner walls of the meter’s housing together with the rotating components of the flow meter. The working principle of a positive displacement flow meter is as follows: as fluid passes through the meter, a certain pressure difference is created between the inlet and outlet. The rotating components of the meter (referred to as rotors) rotate due to this pressure difference, pushing the fluid from the inlet to the outlet. In this process, the fluid fills the meter’s “measurement space” time and again before being sent out to the outlet. Under given conditions of the flow meter, the volume of this measurement space is fixed; by counting the number of rotations of the rotors, it is possible to determine the cumulative volume of fluid that has passed through the meter. 　　Based on their measuring elements, positive displacement flowmeters can be classified into gear-type flowmeters, scraper flowmeters, twin-rotor flowmeters, rotary piston flowmeters, reciprocating piston flowmeters, disk flowmeters, liquid-sealed drum flowmeters, wet gas meters, and diaphragm gas meters, among others. 　　Advantages: (1) High measurement accuracy; (2) The conditions of the piping system in which it is installed have no impact on the measurement accuracy; (3) It can be used for measuring highly viscous liquids; (4) Wide measurement range; (5) As a direct-reading instrument, it can provide cumulative and total values without the need for external power, offering clear readings and simple operation. 　　Disadvantages: (1) The results are complex and the device is large in size; (2) There are significant limitations regarding the type of medium being measured, its diameter, and the operating conditions of the medium; (3) It is not suitable for use in high or low temperature environments; (4) Most of these instruments are only suitable for clean, single-phase fluids; (5) They generate noise and vibration. 　　Application overview: Positive displacement flowmeters, along with differential pressure flowmeters and float flowmeters, are among the three most commonly used types of flowmeters. They are frequently employed for measuring the total volume of expensive fluids such as oils and natural gas. 　　In industrially developed countries, the sales value of PD flow meters (excluding household gas meters and domestic water meters) accounted for 13% to 23% of the total sales volume of flow meters in recent years; in China this figure is around 20%. In 1990, the production volume (excluding household gas meters) was estimated to be 340,000 units, of which elliptical gear type and worm gear type meters accounted for approximately 70% and 20% respectively.

According to the information above, are household gas meters and household water meters also types of positive displacement flow meters? :)

There are many types of positive displacement flow meters, such as gear pumps, elliptical gear pumps, and twin-rotor pumps. Different types come at different prices, and it’s also hard to say anything about prices varying between different manufacturers. In general, I think they are more expensive than vortex flow meters and orifice plates.