A positive displacement flow meter is the most accurate flow meter. It is also called a fixed displacement flowmeter or PD flowmeter. It uses mechanical measuring elements to continuously divide the fluid into single known volume parts, and measures the total volume of the fluid according to the number of times the measuring chamber is repeatedly filled and discharged with the volume part of the fluid. It is widely used in various industries. The following is an introduction to a positive displacement flow meter.
What is a Volume Flow Meter?
Volume Flow
Volume Flow Meter
How does a Volume Flow Meter Work?
Volumetric flow meters measure the volume of fluid flowing past a specific point per unit of time. They do this by either directly counting the volume of fluid flowing through a chamber or by measuring the fluid velocity and then calculating the volumetric flow rate.
Volumetric flow meters work by filling and emptying a chamber of known volume. As fluid flows into the chamber, it is pushed out, and the number of times this cycle repeats is counted. By knowing the volume of the chamber and the number of cycles, the total volumetric flow rate can be determined.
Advantages and Disadvantages of Volume Flow Meters
Advantages
- High accuracy and reliability. They can measure fluid volumes very accurately.
- They can be used to measure a wide range of fluid types. Including liquids, gases, and steam.
- Wide operating range. They can operate over a wide range of temperatures and pressures.
- Low maintenance. Some types of flow meters, such as ultrasonic flow meters, require very low maintenance because they have no moving parts.
Disadvantages
- Sensitivity to fluid properties. May be affected by changes in fluid viscosity, density, and temperature
- Poor measurement of complex solid-liquid mixtures.
- Requires frequent calibration checks and may be sensitive to vibration.
- Initial installation costs may be high. Especially for ultrasonic and electromagnetic flow meters.
Applications of Volume Flow Meters
Water and Wastewater Treatment:
Measure raw water, clean water and wastewater flows. Ensure efficient treatment processes and comply with regulations.
Oil and Gas:
Monitor crude oil, oil and gas flows to ensure accuracy in delivery and storage.
Chemical Industry:
Measure chemicals and solvents to control flows during chemical reactions.
Food and Beverage:
Used in processes as diverse as beverage production and sugar beet processing. Accurately proportion ingredients and manage sanitary wastewater.
Pharmaceuticals:
Precise dosing and batch control to ensure precision in pharmaceutical production.
HVAC Systems:
Measure air and water flows to optimize system performance and energy savings. Ensure efficient operation of HVAC systems.
Types of Volume Flow Meters
Positive Displacement Flow Meter
These high-precision volumetric meters measure volume directly by utilising a mechanical chamber to periodically partition and discharge a fixed volume of fluid.
Positive displacement flow meters use mechanical means to systematically fill and empty a chamber (such as a piston or gear) to directly measure volume.
Circular Gear Flow Meter
This meter measures fluid flow based on the principle of positive displacement, with a pressure differential driving the rotation of gears to displace a fixed volume of medium. It supports multiple signal outputs.
Its accuracy is unaffected by viscosity, and it requires no straight pipe sections, making it suitable for high-viscosity liquids such as oils and syrups. It is commonly used for trade metering in small to medium-sized pipe diameters.
Rotary Piston (Roots) Flow Meter
A positive displacement instrument in which the rotor rotates to deliver a metered volume of fluid; temperature and pressure compensation are available as options.
It offers a wide measurement range and large bore sizes, with accuracy unaffected by flow patterns, making it suitable for natural gas and refined petroleum products; it is frequently used in high-flow industrial and commercial applications.
Scraper Flow Meter
Employs a positive displacement structure for flow measurement, with wear-resistant scrapers forming a sealed chamber.
It can withstand trace solid particles in the medium and offers excellent resistance to fouling, making it suitable for high-viscosity, complex fluids containing impurities, such as crude oil and heavy oil.
Rotary Piston Flow Meter
It achieves quantitative measurement through the reciprocating motion of an eccentric piston.
Compact, cost-effective, with low pressure drop and simple maintenance, it is suitable only for clean liquids and is commonly used in civil water supply, fuel oil, and small-scale lubricating oil applications involving medium to low flow rates.
Velocity flowmeter
They first detect the fluid velocity and then calculate the volumetric flow rate based on the cross-sectional area of the pipe; this type offers the widest range of models and is the most widely used.
Vortex Flow Meter
The vortex flow meter uses the von Karman effect to measure the volume flow of gas, steam or liquid. When the fluid flows through the dust collecting bar of the vortex flow meter, vortices are formed. The frequency of vortex shedding is proportional to the fluid velocity. Temperature and pressure compensation can be configured.
The volume flow of the vortex flow meter is not affected by thermal parameters such as temperature, pressure, density or viscosity of the measured fluid. Usually ,no separate calibration is required. It can measure the flow of liquids, gases or steam.
Turbine Flow Meter
Turbine flow meters use a rotating turbine to measure velocity. These flow meters utilize turbine blades that rotate as the fluid flows. The speed of the turbine is proportional to the flow rate. This allows for accurate volumetric measurement. They have a wide flow range and high accuracy. They are ideal for oil, gas, and petrochemical applications.
Rotameter
A rotameter is a device that measures the flow of liquids and gases by using a tapered tube and a float that moves with the fluid. A rotameter consists of a tapered tube and a float.
The height of the float corresponds to the flow rate of the fluid. This makes these flow meters useful in a variety of industries. Including healthcare and chemical processing.
Electromagnetic Flow Meter
Electromagnetic flow meters measure the flow of conductive liquids using Faraday’s law of electromagnetic induction. The magnetic field induces a voltage proportional to the liquid flow rate, thus measuring the flow rate. They are commonly used in wastewater treatment, mining, and food and beverage industries.
Ultrasonic Flow Meter
Ultrasonic flow meters use sound waves (ultrasound) to measure the flow rate of a fluid. They send ultrasonic pulses through the fluid and measure the time it takes for the pulse to travel up and down. They are used in a wide variety of applications, including liquids, gases, and steam.
You have learned about the relevant knowledge of the positive displacement flowmeter. You can choose the positive displacement flowmeter that suits you. If you need a mass flowmeter, you can also choose a mass flowmeter. The following is a detailed introduction.
Criteria for Selecting a Volume Flow Meter
When selecting a volume flow meter, the following factors should be considered.
- Connection size and type: Pipe diameter, connection port size and type (clamp, flange or thread) to ensure proper installation.
- Flow rate: Determine the maximum and minimum flow rates expected in the system.
- Consider the purpose of the measurement: Is it measuring instantaneous flow or total volume?
- Output signal: Determine the type of signal required (e.g., analog, digital) and its compatibility with the control system.
- Operating parameters: Make sure the flow meter can operate within the required temperature and pressure range.
- Cost: Consider the initial purchase price as well as the cost of installation, maintenance and potential repairs.
- Environment: Consider ambient temperature, humidity and any potential electrical interference.
- Industry requirements and certifications: Check for any specific certifications or approvals required for the application.
What is Mass Flow and Volumetric Flow?
Mass flow and volume flow are two important concepts in fluid dynamics, and they differ in many aspects.
Definition and Representation Method
Volume flow: refers to the volume of fluid flowing through a certain section in unit time, usually represented by the symbol “V” or “Q”, and the unit is cubic meters per second (m³/s), liters per second (L/s), etc.
Mass flow: refers to the mass of fluid flowing through a certain section in unit time, usually represented by the symbol “m”, and the unit is kilograms per second (kg/s), kilograms per hour (kg/h), etc.
Focus and Influencing Factors
Volume flow: focuses on the volume change of the fluid, which is affected by factors such as fluid density, temperature, and pressure. In particular, the volume of gas will change significantly with changes in temperature and pressure.
Mass flow: focuses on the mass change of the fluid, which is mainly affected by the density of the fluid. When the density is constant, the mass flow is proportional to the volume flow.
Application Scenarios and Significance
Volume flow: widely used in chemical, petroleum, water treatment and other fields, which helps to understand the flow state of the fluid and the pipeline transportation capacity.
Mass flow: It is particularly important in situations where the quality of fluids needs to be accurately measured, such as hydrocarbon gas mass flow measurement in the petrochemical industry, dairy products and wine mass flow measurement in the food industry, etc. It is of key significance to ensure product quality and optimize production processes.
Measurement Methods and Instruments
Volume flow: The measurement methods include throttling device method, velocity area method, volumetric method, etc., and commonly used instruments include electromagnetic flow meter, vortex flow meter, etc.
Mass flow: The measurement methods include direct measurement method and indirect measurement method, and commonly used instruments include Coriolis mass flow meter, thermal mass flow meter, etc.
Measurement Principle
Volume flow meter: The flow is measured by measuring the volume of fluid flowing through the pipeline per unit time, usually using the physical effects (such as rotation, displacement, etc.) generated when the fluid passes through the measuring element for measurement.
Mass flow meter: Directly measure the mass flow of the fluid based on the physical effects (such as Coriolis force, heat conduction effect, pressure difference, etc.) generated when the fluid flows in the pipeline, without the need to indirectly calculate by measuring the volume flow and density.
Measurement Object
Volume flow meter: mainly used to measure the volume flow of fluids, including liquids and gases. It cannot directly give the mass flow of the fluid and needs to be converted by measuring density.
Mass flow meter: can be used to measure the mass flow of various fluids, including gas, liquid, etc., and can directly give the mass flow data of the fluid.
Accuracy and Price
Volume flow meter: parameters such as density need to be converted during the measurement process, there may be certain errors, and the price is relatively cheap23.
Mass flow meter: can directly measure the mass flow of the fluid, is not affected by factors such as fluid density, pressure, temperature, etc., and has relatively high measurement accuracy, but the price is also relatively high.
In summary, the volume flow meter is an important tool for measuring fluid flow and plays a vital role in various industries. It can accurately measure fluid flow to optimize operations and improve efficiency. Depending on the application requirements and fluid characteristics, you can choose the right type of flow meter.
We at Sino-Inst have extensive experience and expertise. We offer various types of high-quality, reliable volume flow meters to meet the needs of a wide range of industrial applications. Our commitment to quality and innovation ensures that we provide products that not only meet your expectations but also exceed them.
The team at Sino-Inst is here to help you. If you need more information, please contact us.
