If you work in industrial fluid transfer, you've likely encountered a rotary gear pump — or heard it mentioned in a technical meeting. But what exactly is a gear pump, how does it work, and why are there so many different types? This guide answers the fundamental questions and walks you through the complete picture of rotary gear pump technology.
What Makes Gear Pumps Different?
Most pumps fall into two basic categories: centrifugal pumps and positive displacement pumps. A centrifugal pump spins a wheel (impeller) to create velocity and pressure, relying on speed to push fluid outward. When flow demands or fluid viscosity change, a centrifugal pump's performance degrades rapidly.
A rotary gear pump is a positive displacement pump, meaning it delivers a fixed volume of fluid with each rotation, regardless of downstream pressure or fluid viscosity. Think of it like a syringe plunger: each stroke moves a set volume, regardless of whether you're pushing water or honey.
This fundamental difference makes gear pumps the ideal choice for moving thick, sticky fluids (adhesives, oils, resins) and abrasive slurries (explosives, mining emulsions, paints) where centrifugal pumps would simply recirculate the fluid without moving it forward.
The Anatomy of a Rotary Gear Pump
Despite their industrial reputation, rotary gear pumps are surprisingly simple machines with only five major components:
1. Housing (Pump Case)
The outer metal casing that contains all internal components. The housing is typically cast ductile iron (for standard applications) or stainless steel 304 (for corrosive environments, food processing, chemical transfer). The housing provides structural strength, sealing surfaces, and port connections for inlet and discharge lines.
2. Drive Gear (External Gear)
This gear is mounted on the motor shaft and rotates at pump inlet speed. As it turns, it meshes with the idler gear, creating expanding and contracting chambers. The drive gear pushes fluid from inlet to discharge.
3. Idler Gear (External Gear)
The second gear that meshes with the drive gear. Rotating in the opposite direction, the idler gear completes the fluid displacement cycle. Unlike the drive gear, the idler is not connected to the motor shaft — it's driven by its interaction with the drive gear.
4. Shaft (Drive Shaft) and Bearings
The shaft is the rotating member that connects the motor to the drive gear. High-load roller bearings support the shaft and absorb radial and axial loads created during operation. Bearing quality is critical to pump longevity; worn bearings lead to clearance increases and internal leakage.
5. Seals and Gaskets (Elastomer Components)
Mechanical seals at the shaft outlet prevent fluid from leaking to atmosphere. Internal gaskets and O-rings seal pump compartments. These are the wear items in any gear pump; elastomer selection (nitrile, Viton, EPDM) depends on fluid compatibility and operating temperature.
External vs. Internal Gear Pumps
Most NAPCO pumps are external gear pumps, where both the drive and idler gears are on the same side of the housing and mesh externally (tooth-to-tooth). External gear pumps are simple, field-serviceable, and ideal for high-viscosity fluids.
Internal gear pumps use a large ring gear that surrounds a smaller drive gear. While internal designs offer smooth operation and lower noise, they are more expensive to manufacture and harder to repair in the field. For industrial applications where cost and serviceability matter, external gear pumps dominate.
Why Rubber Gears? NAPCO's Material Advantage
Many gear pump manufacturers use hardened steel or bronze gears. NAPCO pioneered the use of elastomer (rubber) gears for many applications, and this choice delivers critical advantages:
Abrasive Fluid Handling
Explosives emulsions contain grit, sand, and mineral particles. Mining slurries contain ore fines. Elastomer gears are naturally compliant; hard particles embed slightly without breaking the gear tooth. Steel gears, by contrast, are brittle and prone to chipping when exposed to abrasives.
Superior Sealing
Rubber gears deform slightly under load, conforming perfectly to the housing surfaces and minimizing internal leakage (slip). This means better volumetric efficiency and higher effective flow rates. Steel gears maintain rigid tooth profiles, allowing more fluid to leak past.
Noise and Vibration Reduction
The elasticity of rubber gears dampens the gear mesh noise inherent in any positive displacement pump. Applications in manufacturing plants or chemical terminals appreciate the quieter operation.
Material Compatibility
NAPCO offers multiple elastomer options to match your fluid chemistry. Nitrile gears handle most petroleum, chemical, and adhesive applications up to 240°F. Viton gears extend compatibility to higher temperatures and aggressive solvents. Urethane gears are available for specialized applications.
Where Are Gear Pumps Used? Key Industries
Rotary gear pumps are the workhorse of heavy industrial fluid transfer. Here are the primary markets:
- Mining & Explosives:Transfer of emulsion explosives, water-based slurries. See our Explosives & Mining Industry page
- Adhesives & Sealants:High-viscosity adhesives, polyurethane, epoxy resins. See our Adhesives & Sealants Industry page
- Chemical Processing:Corrosive chemicals, process fluids requiring stainless steel construction. See our Chemical Processing Industry page
- Petroleum & Fuel Transfer:Fuel loading, lubricant transfer, terminal operations. See our Petroleum & Fuel Transfer Industry page
- Food & Beverage:Transfer of syrups, oils, flavorings, chocolate using stainless steel pumps. See our Food & Beverage Industry page
- General Industrial:Paints, coatings, inks, lubricants, waste oil, resins, asphalt. See our General Industrial Industry page
Key Performance Specifications Explained
When selecting a pump for your application, you'll encounter three key specifications. Understanding them is essential:
Flow Rate (Gallons Per Minute — GPM)
Flow rate is the volume of fluid delivered per minute at a given input speed and zero backpressure. NAPCO's two primary pump sizes deliver:
- 2" Pump (PA200S/C): Up to 69 GPM @ 190 RPM
- 3" Pump (PA300S/C): Up to 158 GPM @ 280 RPM
Note that flow rate is directly proportional to motor speed. If you run the motor at 95 RPM (half speed), you'll get half the rated flow. This makes gear pumps excellent for variable flow applications.
Pressure Rating (PSI)
NAPCO rotary gear pumps are rated for continuous operation up to 100 PSI. This is the maximum sustained pressure before the relief valve opens. Pressure varies with application; a thin oil might operate at 50 PSI, while a thick adhesive might require the full 100 PSI.
Never exceed the rated pressure. Excessive pressure accelerates wear, damages seals, and risks housing failure.
Shaft Speed (RPM)
Input shaft speed determines flow rate. Most NAPCO pumps operate at motor speeds from 10 RPM to 1800 RPM, depending on your drive system (direct motor coupling, belt drive, gearbox, VFD).
Gear pumps are not speed-limited like centrifugal pumps. You can run them at very low speeds (10 RPM) for metered dispensing, or at high speeds (1800 RPM) for maximum flow. This flexibility is a key advantage over other pump types.
Choosing the Right Pump: Material and Sizing Basics
The first step in pump selection is matching the housing material to your fluid chemistry:
Ductile Iron Housing (Standard)
Ductile iron is cost-effective and handles most industrial fluids: oils, adhesives, explosives emulsions, syrups, and general chemical transfer. All NAPCO models are available with ductile iron construction (PA200C, PA300C, PK200C, PK300C).
Stainless Steel 304 Housing (Specialty)
Stainless steel is required for corrosive chemicals, food processing applications, and environments where iron contamination is prohibited. All NAPCO models are available with stainless steel construction (PA200S, PA300S, PK200S, PK300S).
Once you've selected housing material, the next question is pump size. Do you need a 2" pump (69 GPM) or a 3" pump (158 GPM)? This depends on your flow requirement and system pressure. A quick calculation:
Required Motor Speed = Desired Flow Rate (GPM) ÷ Pump Displacement (GPM/RPM)
For detailed sizing assistance, check our How to Size a Rotary Gear Pump guideor use our interactive pump sizing calculator.
Field Serviceability: The Hidden Advantage
NAPCO rotary gear pumps are engineered for field serviceability. When a pump fails after months or years of service, you don't need to return it to the factory. Instead, your maintenance team can rebuild it on-site using a repair kit.
A repair kit includes all wear parts and elastomers (gears, bearings, seals, gaskets, O-rings) — everything that degrades with age. With basic hand tools and 2-4 hours of labor, your technicians can completely restore a pump to factory specifications.
This approach is critical for remote mining operations, fuel terminals, and manufacturing facilities where a single pump failure can shut down production. Rather than waiting weeks for factory repair, you have your pump running again in hours.
Learn more about repair kits and rebuild procedures in our Maintenance pageand Repairs page. See our complete selection of repair kits.
Continue Your Learning
- Gear Pumps vs. Progressive Cavity Pumps — Technical comparison of pump technologies
- Nitrile vs. Viton Gears: Material Selection Guide — Choose the right elastomer for your fluid
- How to Size a Rotary Gear Pump — Step-by-step sizing guidance
- Field Maintenance for Rotary Gear Pumps — Maintenance schedules and troubleshooting
- PA300S 3" Stainless Steel Pump
- PA200S 2" Stainless Steel Pump
Ready to Specify a Gear Pump for Your Application?
Our engineering team is ready to help with pump selection, sizing specifications, material compatibility, and timeline estimates. Contact us today for a personalized recommendation.
Contact NAPCO Engineering