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A positive displacement meter measures liquid flow by trapping a known volume of fluid and moving that volume through the meter in repeated, countable increments. In industrial service, this makes positive displacement technology especially valuable where accurate volumetric measurement, strong repeatability, and reliable performance at low flow or higher viscosity are required. In BPC’s flowmeter offering, this type of measurement is commonly delivered through oval gear flow meters, alongside turbine and ultrasonic technologies for applications where a different measurement principle is a better fit.
A positive displacement meter is a flowmeter that directly measures the volume of liquid passing through it. Instead of inferring flow from velocity, pressure differential, or transit time, it physically isolates discrete pockets of fluid inside a precision chamber and counts how many of those pockets move from inlet to outlet. That direct volumetric method is the core reason these meters are widely used for batching, dosing, oil measurement, additive injection, chemical metering, and other applications where repeatable volumetric accuracy matters.
In practical BPC applications, the most relevant positive displacement technology is the oval gear flow meter. Oval gear designs are compact, proven, and well suited for industrial liquid services ranging from low-flow chemical dosing to higher-viscosity oils and specialty fluids.
Inside an oval gear positive displacement meter, two precisely machined gears rotate as liquid passes through the measuring chamber. Each partial rotation transfers a fixed amount of fluid. Sensors then detect gear movement and convert it into pulses or other output signals, allowing the control system or display to calculate flow rate and totalized volume. Because the meter is counting actual displaced volume, the output is inherently tied to the liquid passing through the chamber rather than to an inferred velocity profile.
This operating principle provides several important advantages. First, it supports strong repeatability. Second, it performs well where liquids are more viscous, because higher viscosity reduces internal slippage across the measuring elements. Third, positive displacement meters generally do not require long straight pipe runs in the same way some inferential technologies do.
A positive displacement meter is usually selected when the process requires one or more of the following:
For many industrial systems, that makes positive displacement technology a strong choice for oils, polymers, additives, fuels, resins, chemicals, and other clean liquids where viscosity or low-flow accuracy can challenge other meter types. Titan’s oval gear range, which BPC supplies in the US market, is specifically positioned for viscous liquids, oil flow, OEM equipment, hazardous-area compatible sensing options, and chemically resistant constructions.
BPC’s broader flow measurement offering includes positive displacement, turbine, and ultrasonic technologies. That matters because the right meter is not determined by keyword popularity alone. It is determined by the fluid, viscosity, cleanliness, required outputs, accuracy target, allowable pressure loss, and maintenance expectations across the full process system. BPC’s public flowmeter range includes oval gear flowmeters, turbine flowmeters, and ultrasonic flowmeters, including the Atrato ultrasonic flowmeter range.
For example, BPC’s positive displacement oval gear family covers a wide span of flow ranges across different models, from very low flow up to substantially higher industrial rates, with options for aggressive chemicals, high pressure, and non-metallic wetted components.
1. Fluid viscosity
Positive displacement meters often become more effective as viscosity increases, because internal bypass or slippage decreases. This is one of the main reasons they are commonly chosen for oils and similar liquids. However, viscosity also affects pressure drop, so the selection must consider both measurement performance and hydraulic impact.
2. Fluid cleanliness
Positive displacement meters rely on tight internal clearances. That means the liquid must be clean enough for the meter design. Titan’s oval gear installation guidance calls for an upstream filter of at least 80 microns. Abrasive slurries or dirty liquids can rapidly degrade accuracy and service life.
3. Pressure drop
Positive displacement technology can operate at relatively low differential pressure in some oval gear configurations, but pressure loss still must be checked against the process conditions, especially as viscosity rises. Meter selection should always include the expected operating flow range, fluid properties, and acceptable pressure loss through the instrument.
4. Output and controls integration
Positive displacement meters are available with pulse-based outputs and sensing options such as Hall effect, reed switch, or Namur, making them suitable for integration with PLCs, batching controls, and totalization systems. If the process requires analog output, rate display, or advanced communication, the instrumentation architecture should be reviewed at the same time as the meter body and wetted materials.
A positive displacement meter is not the universal answer. It is one measurement principle among several.
A positive displacement meter is typically strongest when the priority is direct volumetric measurement, repeatable batching, or viscous-liquid performance. It is usually best for clean liquids and should be selected carefully if the fluid contains solids or abrasives.
A turbine flow meter is often a strong fit for lower-viscosity liquids, cost-sensitive OEM integration, and compact systems where pulse output is acceptable. BPC’s turbine range includes models for industrial use and NSF-certified variants for beverage and food-related applications.
An ultrasonic flow meter is attractive where no moving parts, low maintenance, or clean-bore construction are priorities. BPC’s Atrato and MetraFlow ultrasonic offerings emphasize wide-range low-flow measurement, no-moving-part reliability, and suitability for specialized clean-liquid services such as ultra-pure water.
For that reason, selection should start with the application, not the technology label. The most reliable system outcome comes from matching the meter type to the process conditions and the control objective.
Positive displacement meters are commonly used for:
What is the main advantage of a positive displacement meter?
The main advantage is direct volumetric measurement. A positive displacement meter counts known volumes of liquid as they pass through the measuring chamber, which supports strong repeatability and dependable batching performance.
Are positive displacement meters good for viscous liquids?
Yes. Positive displacement meters are often an excellent choice for viscous liquids because increasing viscosity reduces internal slippage and can extend useful measurement performance at lower flows.
Can a positive displacement meter handle dirty or abrasive fluids?
Usually not well, unless the specific meter and service conditions have been carefully reviewed. Tight internal clearances make positive displacement meters sensitive to solids and abrasion, so clean-liquid service and upstream filtration are important.
Does a positive displacement meter require straight pipe runs?
In many cases, no extensive straight upstream and downstream runs are required compared with some other flowmeter technologies. That can simplify installation in compact systems.
A positive displacement meter is a strong technical choice when the application demands direct volumetric measurement, repeatable low-flow performance, and reliable operation on clean liquids, especially where viscosity is elevated. In BPC’s portfolio, oval gear flowmeters provide that capability within a broader flow control offering that also includes turbine and ultrasonic technologies. That wider range matters because the correct flowmeter is the one that improves process reliability, control stability, maintainability, and lifecycle performance for the specific service.
For applications involving oils, chemicals, additives, batching, or other precision liquid duties, contact BPC to compare available configurations and select the right flowmeter for the process.
