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DID YOU KNOW?

Sizing your flow meter is about flow range—not pipe size.

Sizing Your FLOMEC Meter: Why Flow Range Matters

Pipe size doesn’t guarantee accuracy—your min/max GPM does.

A meter sized to your pipe can under-read (or stop counting) at low flow, so always match the meter to your required flow range (and protect accuracy with proper straight-run and pressure-drop planning).

"Did You Know?"
Sizing Your FLOMEC® Meter: Why Flow Range Matters More Than Pipe Size

Did you know that the pipe size in your system doesn’t always match the size of the flow meter you need? Many people assume a 1-to-1 match is correct, but the right meter is always based on flow range, not pipe diameter.

When choosing a meter, several factors come into play, including:

  • Flow demand & available pressure
  • Velocity limits & friction loss
  • Pipe material, elevation & run length
  • Fixture count, fittings, valves & future expansion

Why You Shouldn’t Automatically Choose a Meter the Same Size as Your Pipe

Imagine you have a 2" line and choose a 2" turbine meter (20–200 GPM). If your system only flows 6–25 GPM, the meter becomes inaccurate below its 20 GPM minimum. At approximately 50% of the minimum, it will completely stop counting. Solution: Always size the meter to your required flow range. A 1" turbine meter (5–50 GPM) fits this example perfectly.

Installing a Meter in a Different Sized Line: Key Considerations

1. Maintain Accuracy with Proper Straight-Run

To reduce turbulence, eliminate fittings near the meter:

  • Upstream: 10× the meter’s internal diameter
  • Downstream: 5× the meter’s internal diameter

So, a 1" turbine needs 10" of straight 1" pipe upstream and 5" downstream.

More straight-run pipe is always better. Nearby fittings, like elbows, tees, valves, or reducers, will reduce your accuracy.

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2. Plan for Pressure Drop 

Every component—meters, valves, fittings—adds pressure loss, which can reduce peak flow. 

  • A plumber/pipefitter can estimate added loss
  • FLOMEC® can provide pressure-drop curves when needed

Considering Different Meter Technologies

Each meter style has unique flow capabilities:

Turbine Meters

  • Typical turndown: 10:1 - Minimum flow is 1/10 of the maximum flow
  • Good accuracy within rated range
  • Can read slightly below minimum but with reduced accuracy

Oval Gear Meters

  • Larger turndown: 15:1 or more - Minimum flow is 1/15 of the maximum flow
  • Example: 2" OG meter = 8–120 GPM
  • Cannot operate below minimum flow
  • Minimum rises to 10% of max with very thin fluids

Ultrasonic Meters

  • Very large turndown: up to 150:1 - Minimum flow is 1/150 of the maximum flow
  • Example: 2" ultrasonic meter = 0.92–138 GPM
  • Water-only applications

Need Help Choosing?

Selecting the right meter can be simple, or surprisingly tricky. Our FLOMEC® Product Support team is always here to help you find the best fit for your application.