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Flow Meter

How to Choose the Right Oval Gear Flow Meter: A Simple Guide


Quick Summary: Selecting the right oval gear flow meter requires understanding four key factors: fluid properties (viscosity, compatibility, temperature), system requirements (flow rate, pipe size), output type (mechanical, digital, pulse), and special certifications (sanitary, high-temperature, heated jackets).

For your operations to be accurate, efficient, and safe, selecting the appropriate flow meter is essential. Because of their great accuracy and dependability, oval gear flow meters are a popular choice for many industries, particularly when measuring viscous fluids like oils, fuels, and chemicals.

Positive Displacement Oval Gear Flow Meter
Positive Displacement (PD) Meter - How Oval Gear Technology Works

As a type of positive displacement (PD) meter, they work by trapping a precise amount of liquid between two rotating oval-shaped gears and counting each parcel as it passes through. This direct volume measurement makes them incredibly accurate and less affected by changes in fluid properties.

Why Oval Gear Meters Are the Preferred Choice for Viscous Liquids

Unlike other flow measurement technologies that rely on fluid velocity or differential pressure, oval gear meters measure volume directly. This makes them ideal for:

  • High-viscosity fluids (oils, resins, syrups)
  • Applications requiring custody transfer accuracy
  • Batch filling operations
  • Chemical dosing systems

Step 1: Understand Your Fluid Properties

The first and most important step is to know the properties of the liquid you need to measure. Oval gear meters are designed for clean liquids, as solids can jam the gears and cause damage. Always plan to install a strainer or filter upstream of the meter to protect it.

1. Viscosity: How Thick is Your Liquid?

What is Viscosity? Viscosity is a fluid's resistance to flow, measured in centipoise (cP). Water has a viscosity of 1 cP, while honey is around 10,000 cP.

Oval gear meters excel at handling a wide range of viscosities, but it's a critical factor in your selection:

Low Viscosity (less than 3 cP) - Examples: water, solvents, gasoline
For thin, water-like liquids, some fluid can "slip" between the gears and the chamber wall, which can affect accuracy at very low flow rates. To get the best results, you may need to operate at a slightly higher flow rate to maintain the meter's stated precision.

Medium Viscosity (3 to 1,000 cP) - Examples: diesel fuel, lubricating oils, vegetable oil
This is the ideal range for oval gear meters. They provide excellent accuracy with these fluids because there is minimal slippage.

High Viscosity (above 1,000 cP) - Examples: honey, grease, thick resins, molasses
Very thick fluids create more resistance, leading to a higher pressure drop across the meter. For these applications, look for meters with special "high viscosity" rotors that reduce pressure drop by up to 50% without sacrificing accuracy.

2. Chemical Compatibility

The flow sensor's materials must be able to withstand the liquid without corroding or degrading. This applies to every part that touches the fluid, known as "wetted parts."

Material Selection Guide for Oval Gear Flow Meters
Component Material Options Suitable Applications
Body Cast Iron (LC-A) Fuels, oils, greases (non-corrosive)
Body Cast Steel (LC-E) High pressure, low-corrosive fluids
Body Stainless Steel (LC-B, C) Corrosive chemicals, food grade, pharmaceuticals
Rotors (Gears) Aluminum/Cast Iron Petroleum products, hydraulic oils
Rotors (Gears) Stainless Steel Edible oils, chemicals, corrosive liquids

3. Temperature and Pressure Requirements

Ensure the meter you choose is rated to handle your system's normal operating temperature and pressure, as well as any potential maximums.

Standard Operating Ranges:
  • Temperature: -20°C to +60°C (-4°F to 140°F)
  • High-Temperature Models: Up to 200°C (392°F)
  • Pressure: Standard 16 bar, High Pressure up to 63 bar

Step 2: Define Your System Requirements

1. Flow Rate: Minimum, Normal, and Maximum

This is the primary factor that determines the size of the meter. You need to know the full range of flow your system will experience.

Industry Best Practice: Select a meter size where your normal operating flow rate is around 60% of the meter's maximum capacity. This ensures optimal accuracy, reduces wear, and extends service life.

Example: If your normal flow is 25 GPM (95 L/min), choose a meter with a maximum capacity of around 40 GPM (150 L/min) for best performance.

2. Pipe Size and Connection Type

The flow sensor must physically fit into your existing pipework. Oval gear meters are available with various connection types:

  • Flanged connections - ANSI, DIN, JIS, or Table E flanges
  • Sanitary (Tri-Clover) - For hygiene-critical applications in food, beverage, and pharmaceutical industries
Installation Advantage: Unlike turbine or vortex meters, oval gear meters do NOT require straight pipe runs before or after installation. This gives you flexibility to install them in tight spaces, right after a pump or elbow, without affecting accuracy.

Step 3: Choose Your Output and Display Options

Different output types for oval gear flow meters
Output Options: (a) Mechanical Display (b) Resettable Totalizer (c) Pulse Output (d) Digital Display

Available Output Types

A. Mechanical Display Only
Simple, non-powered counter on the meter itself. Robust and reliable for local readings where you don't need system integration. No external power required.

B. Mechanical Display with Resettable Batch Totalizer
Includes a manually resettable counter for individual batch measurements. Perfect for filling operations where you need to track individual batches.

C. Electronic Output (Pulse or 4-20mA)
Mechanical display plus electronic signals that can be sent to PLCs, batch controllers, or remote displays. Ideal for automated systems and SCADA integration.

D. Integral Digital Display
Battery-powered or loop-powered LCD/LED display mounted on the meter. Shows real-time flow rate and total volume with multiple communication options (4-20mA, pulse, RS485, HART).

Step 4: Consider Special Requirements and Certifications

1. Heating Jackets for Viscous or Solidifying Liquids

Heating jacket oval gear flow meter
Heating Jacket Design for High-Viscosity Applications

For liquids that easily solidify or are extremely viscous at ambient temperatures (asphalt, bitumen, heavy resins, chocolate), a meter with a heating jacket is essential. The jacket allows circulation of steam or hot oil to maintain fluid temperature and prevent solidification inside the meter.

2. High-Temperature Applications

For processes consistently above 60°C (140°F), high temperatures can damage electronic components. Meters equipped with cooling fins or heat sinks dissipate heat effectively, protecting the electronics and extending service life.

3. Sanitary Design for Food and Pharmaceutical

Sanitary oval gear flow meter
Sanitary Design with Tri-Clover Connections

Food, beverage, and pharmaceutical applications require meters that meet strict hygienic design standards. Features include:

  • Electropolished stainless steel surfaces
  • Tri-Clover sanitary connections
  • Self-draining design
  • 3-A, FDA, or EHEDG certifications
  • CIP/SIP compatible construction

4. Hazardous Area Certifications

If measuring flammable liquids or operating in explosive atmospheres, ensure your meter has appropriate certifications:

  • ATEX (European Union)
  • IECEx (International)
  • FM/CSA (North America)

Frequently Asked Questions

What viscosity range works best for oval gear meters?
Answer :Oval gear meters work best with medium to high viscosity fluids, typically between 10 and 2000 cP. However we have solution for higher viscosity
How do I determine the right meter size?
Choose a meter where your normal operating flow rate is approximately 60% of the meter's maximum capacity. For example, if your typical flow is 25 GPM, select a meter rated for about 40 GPM maximum.
Do oval gear meters require straight pipe runs?
No! One of the biggest advantages of oval gear meters is that they do NOT require upstream or downstream straight pipe runs. You can install them immediately after pumps, elbows, or valves without affecting accuracy.
What maintenance do oval gear meters need?
Regular maintenance includes checking and cleaning the upstream filter/strainer, verifying seal integrity, and periodic calibration verification. For clean fluids, maintenance intervals can be 12-24 months or longer.
Can I use an oval gear meter with dirty or contaminated fluids?
Oval gear meters require relatively clean fluids. Always install a filter or strainer (typically 100-200 mesh) upstream to protect the gears from particles that could cause jamming or wear.

Your Selection Checklist

By answering these questions, you can confidently choose the right oval gear meter:

  • Fluid: What is my liquid, and what is its viscosity, temperature, and pressure?
  • Compatibility: What materials (body, rotors, seals) are compatible with my fluid?
  • Cleanliness: Is my fluid clean? (If not, I need a filter)
  • Flow Rate: What are my minimum, normal, and maximum flow rates?
  • Installation: What is my pipe size and preferred connection type?
  • Output: How do I need to read the data (mechanical, digital display, pulse)?
  • Certifications: Do I need approvals for hazardous areas, custody transfer, or sanitary use?

Conclusion: Making the Right Choice

Choosing the right oval gear flow meter doesn't have to be complicated. By systematically considering your fluid properties, system requirements, data needs, and any special certifications, you can select a meter that will provide accurate, reliable measurements for years to come.

This careful selection process is a small investment that pays off with:

  • Improved process control and consistency
  • Reduced waste and material costs
  • Lower total cost of ownership
  • Minimal maintenance requirements
  • Extended equipment lifespan

Need help selecting the right meter for your application? Our technical team is available to provide free consultation and sizing assistance. Contact us today with your fluid properties and flow requirements.


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