Selecting a turbine meter based only on pipe size can lead to poor measurement performance or no readings at all. A 4-inch process line does not necessarily require a 4-inch flow meter, especially when the actual flow rate is relatively low.
For turbine flow meters, the more important question is whether the expected minimum, normal, and maximum flow rates fall within the meter’s usable measuring range.
When pipe size and flow rate do not match, Turbines, Inc. can help size the meter around the actual operating conditions and, when appropriate, manufacture custom “by-meter” configurations that maintain the required process connections while using a measuring section better suited to the application’s flow range.
Why Pipe Size Alone Shouldn’t Determine Flow Meter Size
Pipe diameter and flow rate are related, but they are not interchangeable when selecting a flow meter.
A large pipe may have been selected because of system design requirements, future capacity, pressure-drop considerations, or existing facility standards. That does not mean the process is currently operating at a flow rate appropriate for a meter with the same nominal size.
What Happens When a Flow Meter Is Oversized?
If a turbine flow meter is too large for the actual flow rate, fluid velocity through the meter may be lower than desired.
This can cause the application to operate near or below the meter’s recommended minimum flow range, where measurement performance may be reduced.
Instead of asking:
“What size is the pipe?”
The better starting point is:
“What flow rates will actually pass through the meter?”
Start With Minimum, Normal, and Maximum Flow
Proper turbine flow meter sizing should begin with the application’s operating flow range.
Before selecting a meter, determine:
- Minimum expected flow
- Normal operating flow
- Maximum expected flow
The normal operating flow is particularly important because the meter should ideally spend most of its operating time comfortably within its specified measurement range.
Maximum flow should still be considered, but sizing a meter solely around an occasional peak can result in a meter that is unnecessarily large during normal operation.
Don’t Forget Low-Flow Conditions
Startup, shutdown, batching, reduced production, and variable-speed pumping can all create periods where flow is substantially below the application’s maximum rate.
These conditions should be considered when selecting the appropriate turbine meter size.
Size the Meter for Flow Rate, Not Just the Pipe
Once the operating range is known, Turbines, Inc. can evaluate which meter size is best suited to the actual flow requirement.
Additional factors may include:
Fluid Properties
Fluid density and viscosity can influence turbine meter performance, particularly at lower flow rates.
Temperature
Operating temperature affects material selection, bearing configuration, electronics, and other meter components.
Pressure
The meter body and connections must be suitable for both normal operating pressure and the application’s maximum possible pressure.
Pressure Drop
Reducing the internal flow area increases fluid velocity, but it can also increase pressure loss. The goal is therefore not simply to use the smallest possible meter.
The correct meter balances measurement range, velocity, pressure drop, and the overall requirements of the process.
Using a By-Meter When Pipe Size and Flow Rate Don’t Match
One solution available from Turbines, Inc. is a custom configuration commonly referred to as a by-meter.
What Is a By-Meter?
A by-meter allows the process connections to accommodate the customer’s existing piping while the turbine measuring section is sized according to the actual flow requirement.
For example, an application may have a 6-inch process line but only require a flow range that is better suited to a smaller turbine measuring section.
Rather than simply supplying a 6-inch turbine meter that may be oversized for the flow, Turbines, Inc. can evaluate a configuration that transitions from the larger process connection to the appropriately sized measuring section.
This provides a custom solution built around the application rather than forcing the application to fit a standard meter size.
Why Use a By-Meter?
By-meter configurations can be particularly useful for:
- Large process lines with relatively low flow rates
- Existing systems where piping changes are difficult
- Skid systems with fixed flange requirements
- Retrofit or replacement projects
- Applications requiring specific flange sizes or pressure classes
They can also reduce the need for customers to source separate reducers, expanders, and additional piping components around the meter.
Example: A 4-Inch Line With 100 GPM
Consider a system with a 6-inch process line carrying approximately 100 GPM.
Selecting a flow meter based solely on the 4-inch connection could result in a meter whose measuring range is not ideal for the application’s actual flow.
Instead, the application should be evaluated based on the 100 GPM operating requirement.
A smaller turbine measuring section may provide a more appropriate flow range. A custom by-meter can then transition from the customer’s 4-inch connections into the properly sized measuring section and back to the required outlet connection.
The final configuration maintains compatibility with the existing system while allowing the meter itself to be sized around the flow.
Installation Still Matters
When transitioning between pipe sizes, the surrounding piping arrangement should also be considered.
Reducers, elbows, valves, pumps, and other upstream disturbances can affect the velocity profile entering a turbine flow meter.
Maintain a Stable Flow Profile
Proper upstream and downstream piping helps ensure that fluid enters the meter with a stable flow profile.
Applications with limited straight run or significant upstream disturbances may require additional evaluation or flow conditioning.
Information to Provide When Requesting a Flow Meter
When pipe size and flow rate do not match, providing detailed operating conditions allows Turbines, Inc. to recommend the appropriate configuration.
Include:
- Pipe size
- Connection type
- Minimum flow
- Normal flow
- Maximum flow
- Fluid
- Viscosity, if available
- Operating temperature
- Operating and maximum pressure
- Accuracy requirements
- Available straight pipe
- Installation limitations
Need a Flow Meter Sized for Your Actual Flow?
Your turbine flow meter does not always need to be the same size as your process piping.
Turbines, Inc. can evaluate your actual flow conditions and determine whether a standard meter, reduced meter configuration, or custom by-meter is the best solution.
Send us your pipe size, flow range, fluid, pressure, and temperature, and our team can help determine the appropriate turbine flow meter configuration for your application.