When it comes to measuring the flow of liquids—especially those with high viscosity or at low flow rates—positive displacement (PD) flow meters offer unmatched precision and reliability. From chemical batching to oil metering, these robust instruments provide volumetric accuracy where other flow technologies may fail.
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What Is a Positive Displacement Flow Meter?
A przepływomierz wyporowy is a volumetric flow measurement device that directly counts the volume of liquid passing through it. Unlike other flow meters that infer flow based on velocity, pressure drop, or thermal properties, PD flow meters physically trap and release precise volumes of fluid, ensuring high-accuracy measurement.
They are particularly well-suited for:
- High-viscosity liquids (like oil, honey, or glue)
- Low flow rate conditions
- Applications requiring totalization (batching, dispensing, blending)
Positive displacement meters are often regarded as mechanical counters—each rotation, oscillation, or movement corresponds to a fixed volume of fluid, enabling accurate totalization without the need for complex calculations.
How Does a Positive Displacement Flow Meter Work?
At the core of every PD meter is a chamber oraz mechanical components (e.g., gears, pistons, rotors) that rotate or move to trap a fixed volume of fluid. Each cycle of movement corresponds to a known, consistent volume. By counting these cycles, the meter calculates total volume oraz natężenie przepływu.
Here’s a simplified process of how it works:
- Fluid Enters the Meter The incoming fluid is directed into the measuring chamber.
- Mechanical Displacement Internal rotating or oscillating components (e.g., gears, disks, pistons) trap a fixed volume of fluid.
- Fluid Discharge As the chamber moves, the fluid is pushed out and exits the meter.
- Volume Counting Each movement is detected by sensors or magnets, and the cumulative count represents the total volume passed.
Because the meter measures flow volumetrically, its accuracy is largely unaffected by changes in fluid properties such as viscosity, density, or turbulence—making it ideal for precise, repeatable measurement in challenging conditions.
Types of Positive Displacement Flow Meters
There are several different types of PD flow meters, each suited for different flow rates, fluid types, and applications. Here are the most commonly used varieties:
1. Gear Flow Meters
Jak działają:
Gear flow meters use two intermeshing gears—typically oval or helical—to form pockets of fluid that are moved from the inlet to the outlet.
Najlepsze dla:
- High-viscosity liquids (oil, glue, syrup)
- Low flow conditions
- Precise dispensing
- Zaprojektowany do cieczy o niskim przepływie od 0,6 l/godz.
- Szeroki współczynnik obrotu 150:1
- Zdolny do pomiaru silnie korozyjnych mediów, w tym kwasu siarkowego, kwasu fluorowodorowego i innych agresywnych chemikaliów.
- Zaprojektowany do pomiaru płynów o wysokiej lepkości, obsługuje wymagające media, takie jak syrop, stopiony asfalt i miód z niezawodną dokładnością.
- Precyzyjny pomiar z dokładnością do ±0,5%
2. Rotary Vane Flow Meters
Jak działają:
A rotor with multiple vanes turns inside a cylindrical housing. Each rotation traps a known volume of liquid and transfers it through the meter.
Najlepsze dla:
- Water-based fluids
- Heating oil and fuel
- Industrial process flows
3. Piston Flow Meters
Jak działają:
Fluid is drawn into and pushed out of chambers by oscillating or rotating pistons. Each stroke displaces a fixed volume.
Najlepsze dla:
- Clean, low-viscosity fluids
- Wtrysk chemiczny
- Pharmaceutical and medical dosing
4. Nutating Disk Flow Meters
Jak działają:
A disk mounted on a central ball “wobbles” (nutates) inside a chamber, displacing fluid in fixed volumes per cycle.
Najlepsze dla:
- Residential water meters
- Beverage dispensing
- Custody transfer systems
5. Bi-Rotor Flow Meters
Jak działają:
Two rotors rotate inside a cavity, creating fluid pockets that are displaced through the meter. These meters have minimal internal friction, making them ideal for sanitary applications.
Najlepsze dla:
- Food-grade fluids
- Farmaceutyki
- Viscous fluids like oil, resin, or syrup
- Custody transfer systems
- Wysoka dokładność do ±0,1 %, wysokie ciśnienie procesowe do 110 bar (1595 psi)
- Wyjątkowo długa żywotność, niskie koszty utrzymania
- Brak oscylujących, posuwisto-zwrotnych lub przesuwnych części lub korb powodujących zużycie lub zakłócenie zrównoważonego ruchu obrotowego.
- Stabilny podczas pracy z niskim głosem
- Dobra wydajność przeciwzakłóceniowa i długa żywotność
- Silne zastosowanie do zmian lepkości
6. Oval Gear Przepływomierze
Jak działają:
Oval gear meters use two interlocking oval-shaped gears that rotate with the flow of fluid. Each rotation displaces a known volume, and the number of rotations is proportional to the total volume passed through.
Najlepsze dla:
- Viscous fluids like oil, resin, or syrup
- Płynna praca wirnika spiralnego z minimalnymi wibracjami zapewnia stałą wydajność
- Szeroki zakres pomiarowy z dobrą powtarzalnością
- Precyzyjny pomiar z dokładnością do ±0,2%
- Niewrażliwy na zmianę lepkości
- Zoptymalizowany do pomiaru cieczy o wyższej lepkości
- Prosta instalacja bez konieczności prowadzenia prostych rur
Zalety przepływomierzy wyporowych
Positive displacement flow meters offer many performance and operational advantages, making them the go-to solution in applications where accuracy and repeatability are critical.
- Direct Measurement of Volume: They don’t estimate or infer—PD meters measure the actual fluid volume passing through, which eliminates many common sources of error.
- High Accuracy at Low Flow Rates: They are among the most accurate flow meters at very low flow levels, which makes them ideal for dosing and micro-batching applications.
- Niewrażliwość na właściwości płynu:PD meters are not affected by fluid density, viscosity, or temperature to the extent that other technologies are.
- No Need for Straight Pipe Runs: Unlike turbine or ultrasonic meters, PD meters don’t require long upstream or downstream pipe lengths, which is a major benefit in compact installations.
- Excellent Repeatability: Their mechanical design ensures highly consistent performance over time.
- Totalizing and Batch-Friendly: Perfect for batching, filling, or blending systems where cumulative volume matters.
Disadvantages of Positive Displacement Flow Meters
While PD flow meters offer numerous benefits, there are some limitations to consider when choosing this technology.
- Not Ideal for Dirty Fluids: Solids, debris, or particulates can damage internal moving parts or cause clogging.
- Mechanical Wear and Tear: Over time, mechanical components can wear down, especially if proper filtration or maintenance is not observed.
- Size and Cost at High Flow Rates: For high-flow applications, PD meters become bulky and expensive compared to other technologies.
Recommended Fluids and Mediums for PD Flow Meters
Positive displacement flow meters work best with clean, viscous, and incompressible liquids. Here are common media types that are well-suited for PD technology:
Oils
- Hydraulic oil
- Lubricating oil
- Engine oil
- Ropa naftowa
Substancje chemiczne
- Resins and adhesives
- Rozpuszczalniki
- Additives and catalysts
Żywność i napoje
- Honey
- Syrup
- Flavor concentrates
- Milk and dairy products
Pharmaceutical and Cosmetic
- Glycerin
- Alcohol-based fluids
- Emulsions
- Liquid medication
Zastosowania przepływomierzy wyporowych Przepływomierze
Thanks to their accuracy and reliability, PD flow meters are used in a variety of industries and processes. Here are some of the most common use cases:
1. Chemical Injection and Dosing
In water treatment, oil refining, and specialty chemical manufacturing, PD meters ensure precise injection of expensive or reactive chemicals.
2. Oil and Fuel Measurement
They are widely used in lube oil blending plants, diesel fuel transfer systems, and engine testing labs to measure and totalize fuel flow.
3. Food and Beverage Processing
In high-viscosity food products such as honey or syrups, PD meters ensure consistent dosing during filling and packaging.
4. Cosmetics and Personal Care
PD meters accurately dispense lotions, creams, and gels in controlled environments.
5. Pharmaceutical Manufacturing
For high-value drugs and bio-fluids, PD meters are used in ultra-precise filling, mixing, and formulation applications.
6. Paints and Coatings
In pigment and resin applications, PD meters help maintain proper ratios and minimize waste.
Explore Metlan’s PD Flow Meter Solutions
Przy Metlan Instruments, we offer industry-grade positive displacement flow meters tailored for low flow, high-viscosityoraz precision-critical aplikacje.
Need help finding the right meter for your system? Contact us today—we’ll help you select the perfect solution for your application.
