Unique Pump System, Kailash Industrial Complex, Vikhroli West
A gear pump is a type of positive displacement pump that moves fluid by trapping a fixed volume between rotating gear teeth and the pump casing. Unlike centrifugal pumps that rely on velocity, gear pumps deliver precise, pulse-free flow — making them ideal for oils, chemicals, resins, polymers, and other viscous fluids in industrial applications. This comprehensive guide explains how gear pumps work, the differences between external and internal designs, how to select the right pump, and how gear pumps compare to AODD pumps.
Also Read: Gear Pump Installation
Gear pumps operate on a simple three-phase cycle: suction, transport, and discharge.
Because the gears mesh tightly, fluid cannot flow backward — ensuring steady, pulse-free output. Flow rate is directly proportional to rotational speed, making gear pumps ideal for metering and dosing applications.
| Feature | External Gear Pump | Internal Gear Pump |
|---|---|---|
| Design | Two identical gears side by side, rotating into each other | One internal gear (rotor) drives an external idler gear; crescent seal separates ports |
| Pressure Capability | Higher pressures (up to 70 kg/cm²) | Moderate to high pressures (typically up to 40–50 kg/cm²) |
| Viscosity Range | Suitable for low to medium viscosity | Excellent for high viscosity (up to 100,000 CST) |
| Temperature Tolerance | Standard temperature range | Handles high temperatures; steam jacketed options available |
| Noise Level | Higher flow pulsation, more noise | Quieter, smoother operation |
| Flow Direction | Bi-directional if spur gears; herringbone gears are unidirectional | Always bi-directional |
| Cost | More economical, simpler construction | Higher cost due to complex machining |
External Gear Pump Operation
Internal Gear Pump with Crescent Seal
Selection Checklist: Answer these questions before selecting a gear pump:
| Viscosity Range (CST) | Recommended Pump Speed (RPM) |
|---|---|
| Up to 400 | 1440 |
| 400 – 1,000 | 960 |
| 1,000 – 3,500 | 720 |
| 3,500 – 10,000 | 500 |
| 10,000 – 50,000 | 200–300 |
| 50,000 & above | Consult engineer |
While gear pumps are ideal for high-viscosity fluids under pressure, Air Operated Double Diaphragm (AODD) pumps offer different advantages. Understanding both helps in selecting the right pump for your application.
An AODD pump uses compressed air as motive force. A pilot-operated air distribution valve shifts air alternately to two diaphragms, creating a continuous pumping cycle. Key characteristics:
| Criteria | Gear Pump | AODD Pump |
|---|---|---|
| Best for | High pressure, high viscosity, continuous duty | Hazardous areas, abrasives, intermittent duty |
| Pressure capability | Up to 70 kg/cm² | Limited by air supply (typically 6–8 bar) |
| Viscosity range | Up to 100,000 CST | Up to 50,000+ CST |
| Operating cost | Electric motor — lower for continuous operation | Compressed air — higher for continuous operation |
| Dry running | Not allowed — causes damage | Safe for brief periods |
| Solid handling | Poor — tight clearances | Good — can handle some solids |
For continuous operation, compressed air cost can be significant:
| Pump Size | Air Consumption (6 bar, 60 cpm) | Annual Cost (₹3/Nm³, 16hr/day, 300 days) |
|---|---|---|
| ½ inch | ~0.35 Nm³/hr | ~₹5,040 |
| 1 inch | ~1.73 Nm³/hr | ~₹24,912 |
| 2 inch | ~13.8 Nm³/hr | ~₹1,98,720 |
| 3 inch | ~43 Nm³/hr | ~₹6,19,200 |
For permanent installations requiring continuous operation, gear pumps (electric-driven) offer significantly lower operating costs over time.
| Symptom | Likely Cause | Solution |
|---|---|---|
| Pump cycles slowly or stops under load | Insufficient supply pressure or high back-pressure | Increase supply pressure or reduce downstream restriction |
| Reduced flow output | Worn gears or internal clearances | Inspect gear clearances; replace if excessive wear |
| Excessive noise | Cavitation (inlet restriction) or gear wear | Check suction strainer; inspect gears for damage |
| Fluid overheating | Running at excessive pressure or speed | Reduce operating pressure; check relief valve setting |
| Leakage at shaft seal | Worn seal or misalignment | Replace seal; check coupling alignment |
Also Read: Gear Pump Maintenance
Gear pumps are reliable, precise positive displacement pumps ideal for high-viscosity fluids in continuous industrial applications. External gear pump offer higher pressure capability and lower cost; internal gear pumps excel with high-viscosity, high-temperature fluids and quieter operation. When selecting a gear pump, consider viscosity, pressure, temperature, fluid cleanliness, and material compatibility. For applications requiring dry-running capability, abrasive fluid handling, or hazardous-area operation without electricity, AODD pumps may be more suitable — though they carry higher compressed air operating costs for continuous service.
Unique Pump Systems manufactures industrial-grade gear pumps (UA Series) and AODD pumps with extensive material options. Contact our engineering team for selection assistance tailored to your specific fluid, flow, and operating conditions.
