RPD vs Turbine Gas Flow Meters | Understanding the Difference

When it comes to flow measurement, not all flow meters are equal. 

Choosing the right flow meter can make or break your process efficiency. especially when you are choosing between an RPD or a turbine gas flow meter. While both RPD (Rotary Positive Displacement) and turbine gas meters are designed to measure flow rates, they work on entirely different principles.

In this blog, we’ll break down the key differences between RPD vs turbine flow meters, from working principles and fluid compatibility to accuracy, maintenance, and application.

Understanding RPD Gas Flow Meters

RPD (Rotary Positive Displacement) flow meters work on the positive displacement principle.

It measures the flow of gases such as natural gas, biogas, propane, and other hydrocarbon gases.

Working principle of the RPD flowmeter

An RPD flow meter operates by mechanically separating gas and other fluids into the fixed compartment and then monitoring how many times this compartment fills and empties.

The core of the meter consists of two precisely machined, intermeshing rotating elements, commonly lobed rotors or oval gears. They are housed within a measuring chamber.

As gas enters the chamber, it causes these rotors to rotate. Each rotation displaces a specific volume of gas, and this displacement is directly proportional to the flow rate. The number of rotations is detected either mechanically or via a magnetic sensor, which sends signals to a transmitter to calculate the volumetric flow.

RPD Gas Flow Meters are Best For;

Measuring precise volumes of gas, especially in applications with low flow rates, fluctuating flow, or high-viscosity gases.

They are commonly used in:

• Natural gas custody transfer
• Biogas and propane metering
• Industrial gas distribution
• Utility billing systems
• Gas measurement in chemical and process industries

Benefits of the RPD Gas Flow Meters

• RPD gas meters deliver precise measurements, even at low flow rates, where other flow meters may fail.
• They measure the exact volume of gas passing through, which makes it ideal for custody transfer and billing purposes.
• Since they operate mechanically, they are perfect for remote areas where a power supply might not be available.
• RPD flow meters are compact and can be installed in tight spaces with minimal straight-pipe requirements.
• They are known for durability and require less frequent maintenance, which makes them cost-effective.

Limitations of the RPD Gas Flow Meter

• It is not suitable for dirty or contaminated gases, as particles can damage the internal rotors and reduce accuracy.
• Since it involves moving parts, it creates slight flow resistance, which can lead to a drop in pressure, thus, it is not ideal for low-pressure systems.
• While measuring high gas velocity,y the measurement accuracy can decrease.
• It requires a slightly higher initial cost as compared to other mechanical flow meters.

Understanding Turbine Gas Flow Meters

A turbine flow meter measures the flow of gases like natural gas by using the kinetic energy of the gas stream.

When the gas enters the meter, it flows through a stream straightener or flow conditioner. This ensures the gas flows in a straight, laminar direction before it reaches the turbine.

Then the gas flow hits the turbine rotors, which are positioned in the path. The force of the gas causes the rotor to spin.

A magnetic or optical pickup sensor detects the rotational speed of the turbine blades without physical contact.

Each rotation generates a pulse signal, and these signals are directly proportional to the volume of gas flow.

Turbine Gas Flow Meter is Best For;

Measuring clean, dry, and high-pressure gases with a steady flow.

They are commonly used in:

• Natural gas distribution networks
• Commercial gas metering
• Power plants and boiler systems
• Industrial gas flow monitoring
• Compressed air and nitrogen systems

Benefits of the turbine Gas flow meters

• It offers precise measurement, often with an accuracy of ±0.5%, which makes it suitable for billing and custody transfer applications.
• Turbine flow meters create very low resistance to gas flow, which makes them ideal for applications that require high efficiency.
• Turbine flow meters are designed to withstand harsh conditions like high pressure and temperature, thus, they are reliable in demanding environments.
• They can accurately measure the flow rates from high to low.
• Many models of turbine gas meters support electronic signal output.

Limitations of the turbine Gas flow meters

• They require uninterrupted flow. Disturbed or irregular flows can affect the accuracy of a turbine flow meter.
• Since they have moving parts, they can be subjected to wear and tear, thus, they require periodic maintenance.
• They are not suitable for low flow rates, the motor might not spin effectively, and reduce measurement accuracy.
• Particles or liquids in the gas can damage the rotor or bearings

Want to dive deeper? Discover everything you need to know about RPD Flow Meters

Key Differences Between RPD and Turbine Gas Flow Meters

How to Choose the Right Gas Flow Meter for Your Needs

Choose the RPD flow meter if:

• You need high accuracy at low flow rates
• Your gas flow is inconsistent
• The application is for custody transfer or billing
• You’re working with viscous or heavy gases like biogas or propane
• There's limited space for installation (less straight pipe required)
• You need a mechanical meter that works without a power supply

Choose a Turbine flow meter if:

• Your gas is clean, dry, and at high pressure
• Flow is steady and within a high-velocity range
• You're monitoring gas in commercial or industrial systems like power plants or boiler lines
• You prefer a lower initial cost
• You have enough space for proper upstream/downstream piping

Turbine Flow Meters explained. Discover their working, benefits, best-fit applications and more.

Conclusion

Now that you understand the differences between RPD and Turbine gas flow meters, choosing the right one should be much easier. Each type has its strengths. RPD meters are great for accurate measurements at low flow rates, while turbine meters work best in clean, high-pressure conditions with steady flow.

If you're ready to take the next step, consider Burak. We’re one of the leading manufacturers of flow meters, offering both RPD gas meters and Turbine gas meters available with an Electronic Volume Corrector (EVC) model designed for reliable and long-term performance.

Get in touch with us today to find the perfect meter for your application!