Internal Gear Pumps

Internal gear pumps are positive displacement rotary pumps that use two intermeshing gears—an inner gear rotating inside an outer gear—to move fluid from inlet to outlet in sealed pockets. Close internal clearances create a strong liquid seal, enabling consistent flow and good suction performance on viscous products.

OPERATING PRINCIPLE OF INTERNAL GEAR PUMPS 

Internal gear pumps operate based on the interaction between two interlocking gears—an outer gear and an inner gear — within a housing. The key operating principles of internal gear pumps involve.

GEAR INTERACTION

An inner gear (smaller) rotates inside an outer gear (larger). As the teeth unmesh at the inlet, cavities open and draw fluid in; as the teeth mesh at the outlet, cavities reduce and displace fluid to discharge.

FLUID SEALING & Stable flow

Close tolerances between gears and casing minimise slip, delivering repeatable flow per revolution. Flow rate is directly proportional to speed, making internal gear pumps easy to control with variable speed drives.

APPLICATIONS OF INTERNAL GEAR PUMPS

• Asphalt, bitumen and tar handling
• Chemical transfer and ingredient metering
• Oils, fuels and lubricants
• Resins, polymers and polyurethane components (isocyanate/polyol)
• Paints, inks and coatings
• Soaps and surfactants
• Alcohols, solvents, glycols and process additives

WHY BUY INTERNAL GEAR PUMPS FROM AXFLOW? 

AxFlow provides a diverse range of internal gear pumps tailored to various industries. Our experts offer comprehensive support, aiding in pump selection, specification, installation, and maintenance. Reach out to AxFlow for personalized guidance in choosing the ideal internal gear pump for your specific requirements. 

• AxFlow offer a wide range of internal gear pumps including internal and external types, mag driven versions and plastic and alloy wetted materials.
• We are experts in gear pumps having supplied them for over 40 years.
• We have a large team of external and internal pump specialists, and a network of Pump Support Centres spread across the country.

ADVANTAGES OF GEAR PUMPS

Gear pumps are unable to match the pressure capabilities of reciprocating pumps or the flow rates of centrifugal pumps but offer higher pressures and throughputs than vane or lobe pumps. Gear pumps are particularly suited for pumping oils and high viscosity fluids.  There are 2 types of rear pump internal and external both offer the same generic advanatges.

• A smooth flow.
• Low flow capabilties.
• Compact footprint.
• Easy maintenance.
• Can handle viscous fluids.
• Can run at low speeds.
• Self priming.
• Low cost.
• Low Shear

IMPORTANT CONSIDERATIONS WHEN SELECTING INTERNAL GEAR PUMPS 

• Flow Rate: Selecting the right internal gear pump involves considering the desired flow rate. Insufficient flow rates may lead to poor performance, while excessive rates can cause pressure issues and inefficiencies. 
• Viscosity: Internal gear pumps handle a wide viscosity range. Lower viscosity fluids move more easily, while higher viscosity fluids may require adjustments to gear speed for proper handling. 

How to Select an Internal Gear Pump

Selecting the correct internal gear pump is critical for achieving reliable, efficient, and precise transfer of viscous, non-abrasive, and shear-sensitive fluids. Internal gear pumps are a form of positive displacement rotary pump, valued for their smooth, low-pulsation flow, high volumetric efficiency, and ability to handle a wide viscosity range. Proper selection ensures long service life, reduced energy consumption, and stable process control.

1. Define Flow and Pressure Requirements

• Flow rate: Internal gear pumps deliver flow directly proportional to rotational speed. Size the pump to meet required throughput with sufficient turndown for variable operation.
• Differential pressure: Confirm the pump’s maximum continuous and intermittent pressure ratings, accounting for viscosity-related load increases and cold-start conditions.
• Speed: Lower operating speeds reduce wear and improve efficiency when handling high-viscosity fluids.

2. Evaluate Fluid Properties

• Viscosity: Internal gear pumps perform efficiently across a very wide viscosity range, from low-viscosity liquids to extremely viscous products.
• Shear sensitivity: The gentle meshing action makes them ideal for shear-sensitive materials.
• Temperature: Elevated temperatures affect clearances, seals, and lubrication; select materials and tolerances accordingly.
• Chemical compatibility: Match wetted materials to fluid chemistry to prevent corrosion or elastomer degradation.
• Solids content: Best suited for clean or lightly contaminated fluids; abrasive solids accelerate gear and casing wear.

3. Pump Design and Configuration

• Bearing arrangement: Choose between external bearings or product-lubricated designs depending on fluid lubricity.
• Crescent design: The crescent seal separates suction and discharge chambers and must be compatible with fluid temperature and chemistry.
• Mounting orientation: Horizontal or vertical installation based on space and system layout.
• Heating options: Jacketed casings may be required for temperature-controlled or solidifying fluids.

4. Sealing and Drive Options

• Sealing systems: Single or double mechanical seals, packed glands, or magnetic drive options selected based on pressure, temperature, and leakage tolerance.
• Drive control: Use Variable Frequency Drives (VFDs) for accurate flow control, reduced startup torque, and energy efficiency.
• Relief protection: Internal gear pumps require pressure relief valves to protect against dead-heading.

5. Efficiency and Lifecycle Cost

• Select a pump operating near its optimal speed and pressure range to maximise volumetric efficiency.
• Consider ease of maintenance, spare parts availability, and seal accessibility.
• Proper sizing reduces energy consumption, wear, and total lifecycle cost.

Maintenance and reliability

Routine reliability checks typically include inspection for leaks and wear, monitoring performance (flow/pressure at constant speed), verifying lubrication where applicable, and inspecting seals, bearings and fasteners. Maintaining clean suction conditions and appropriate filtration helps protect close internal

FAQs

What fluids are internal gear pumps best suited for?

They are commonly selected for clean, viscous or shear-sensitive liquids such as oils, fuels, resins, polymers, solvents, surfactants and bitumen products (duty dependent).

Do you supply sealless (magnetic drive) internal gear pumps?

Yes. AxFlow supplies magnetically driven internal gear pump options where reducing leakage risk is a priority.

What information do you need to size an internal gear pump?

Fluid type and temperature, viscosity range, required flow, differential pressure/backpressure, suction conditions, solids/abrasives (if any), and any materials or sealing requirements.

Who do I contact for internal gear pump support?

PD Pumps Team — Phone: 01753 255 609 — Email: pd.pumps@axflow.co.uk