The main advantage of an internal gear pump over an external gear pump is its smooth, low-pulsation and typically quieter flow. An external gear pump, however, is often selected for its simple construction, compact size and cost-effective operation in standard hydraulic circuits.
Neither design is automatically better for every system. The correct choice depends on the fluid, viscosity, required flow, operating pressure, speed, noise limit, contamination level and duty cycle. This guide explains the practical differences so engineers and buyers can choose a suitable pump configuration.
What Is an Internal Gear Pump?
An internal gear pump is a rotary positive-displacement pump. It typically uses a smaller externally toothed pinion that is driven by the shaft and rotates eccentrically inside a larger internally toothed ring gear. In crescent-type designs, a crescent-shaped partition separates the inlet and outlet chambers.
As the gears come out of mesh at the inlet, the expanding cavities draw fluid into the pump. The fluid travels around the casing in the spaces between the gear teeth. When the gears mesh again near the outlet, the cavities become smaller and discharge the fluid.
This arrangement can provide smooth, low-pulsation delivery. In hydraulic systems, internal gear pumps are often considered for power units and industrial machinery where controlled flow and lower operating noise are important.
Actual pressure, speed, viscosity and temperature limits depend on the pump model, construction materials, shaft seal and operating clearances.
What Is an External Gear Pump?
An external gear pump normally contains two similar gears with external teeth. One gear is connected to the drive shaft, and the second gear is driven by the first.
When the gears separate at the inlet, fluid fills the spaces between the teeth and the housing. Rotation carries the fluid around the outside of the gears. The teeth mesh again at the outlet and force the fluid into the discharge line.
External gear pumps are widely used in mobile and industrial hydraulic systems because their construction is straightforward, compact and easy to integrate. Common applications include agricultural machinery, material-handling equipment, construction machinery, lubrication circuits and general hydraulic power transmission.
Internal Gear Pump vs External Gear Pump: Key Differences
| Selection factor | Internal gear pump | External gear pump |
|---|---|---|
| Gear arrangement | A shaft-driven pinion rotates eccentrically inside an internally toothed ring gear | Two externally meshing gears rotate side by side |
| Flow characteristics | Generally smoother and lower in pulsation | More noticeable flow pulsation may occur, depending on design and speed |
| Operating noise | Often selected when lower noise is important | Noise depends strongly on speed, pressure, gear profile and installation |
| Fluid viscosity | Permitted startup and operating viscosity depend on the selected model and approved hydraulic fluid | Permitted startup and operating viscosity also depend on the selected model and approved hydraulic fluid |
| Inlet characteristics | Some designs provide favorable inlet characteristics, subject to the specified inlet-pressure limits | Inlet line, reservoir position, fluid condition and speed must remain within the specified limits |
| Construction | Uses an eccentric pinion and internal ring gear; crescent-type designs also use a partition | Uses two external gears and a relatively simple housing arrangement |
| Contamination sensitivity | Close clearances require clean fluid | Clean fluid is still essential; contamination accelerates housing and gear wear |
| Typical selection reason | Smooth flow, lower noise and model-specific hydraulic performance requirements | Compact construction, availability and cost-effective hydraulic power |
| Maintenance focus | Pinion, ring gear, bearings or bushings, clearances and shaft seal | Gear teeth, bushings or bearings, side plates, housing and shaft seal |
This table describes general design tendencies rather than fixed performance limits. Buyers should compare the technical data of the actual pump models before making a replacement or purchasing decision.
What Is the Main Advantage of an Internal Gear Pump?
1. Smooth, Low-Pulsation Flow
The internal gear arrangement creates a progressive transfer of fluid through the pump. This can reduce flow pulsation compared with many conventional external gear designs. Smoother delivery can benefit hydraulic systems where pressure variation may affect control stability or operating noise.
2. Lower Operating Noise
Internal gear pumps are frequently used in hydraulic power units and industrial machinery where noise control matters. Their meshing geometry and flow characteristics can help reduce hydraulic pulsation, which is one source of system noise.
Pump noise is not determined by gear type alone. Excessive speed, inlet restriction, trapped air, cavitation, coupling misalignment and poor pipe support can make either pump type noisy.
3. Model-Specific Hydraulic Fluid Range
Depending on the model, an internal gear pump may operate across a broad viscosity range of approved hydraulic fluids. The permitted fluid type, startup viscosity, operating viscosity, temperature and speed must be confirmed from the selected pump’s technical data.
This is a model-specific capability, not a universal advantage of every internal gear pump. Viscosity affects inlet pressure, pump speed, power demand and internal clearances.
4. Good Suction Characteristics
Some internal gear pump designs provide favorable inlet characteristics. However, the inlet line, reservoir position, fluid viscosity and startup conditions must remain within the manufacturer’s specified inlet-pressure limits. The pump must not run dry, and installation above the reservoir should only be used when approved for the selected model.
Where an External Gear Pump May Be the Better Choice
An external gear pump may be more appropriate when the system requires a compact, economical and widely available hydraulic pump. Its relatively simple construction makes it common in mobile equipment and general industrial hydraulic circuits.
Consider an external gear pump when:
- the system uses standard hydraulic oil;
- compact installation is important;
- the application has a stable operating range;
- purchase cost and replacement availability are priorities;
- the existing machine is already designed around an external gear pump;
- flow pulsation and noise are within acceptable limits.
An external gear pump should not be selected only because it appears similar to the existing unit. Displacement, rotation, mounting flange, shaft, port arrangement, rated pressure and speed must be verified.
Where an Internal Gear Pump May Be the Better Choice
Consider an internal gear pump when:
- lower noise is an important system requirement;
- smooth, low-pulsation delivery is needed;
- the selected model’s approved hydraulic-fluid range covers the actual startup and operating viscosity;
- the specified inlet-pressure limits can be maintained throughout startup and operation;
- the available internal gear pump model meets the required pressure, speed and material specifications.
The pump manufacturer should evaluate the complete operating condition, not only the nominal flow and pressure.
Bidirectional operation is a model-specific option rather than an inherent advantage of either gear-pump design. Confirm port design, shaft seal, bearing arrangement and valve orientation before reversing rotation.
How to Select Between Internal and External Gear Pumps
Fluid and Viscosity
Identify the exact fluid and its viscosity at startup, normal operating temperature and maximum temperature. A fluid that becomes very viscous during a cold start can create excessive inlet vacuum and drive torque.
Required Flow and Displacement
Required flow, pump speed and volumetric efficiency determine the necessary displacement. Do not select displacement from the pump body size alone.
Working and Peak Pressure
Provide both continuous working pressure and expected peak pressure. A pump that can tolerate a short pressure peak may not be suitable for continuous operation at that value.
Inlet Conditions
Check tank position, suction-line length, line diameter, filter restriction, fluid temperature and the possibility of air entering the inlet. Poor inlet conditions can cause cavitation, noise, unstable flow and premature wear.
Noise Requirement
If the system operates indoors, near workers or in noise-sensitive machinery, the internal gear option may deserve priority. The complete installation must still address motor noise, coupling alignment, valve pulsation and pipe vibration.
Mounting and Connection
For replacement projects, confirm:
- mounting flange;
- shaft type and dimensions;
- inlet and outlet port positions;
- direction of rotation;
- displacement;
- operating speed;
- continuous and peak pressure;
- seal material;
- available installation space.
Internal and external gear pumps are not automatically interchangeable even when their flow ratings are similar.
Information Required for a Pump Recommendation
To help the POOCCA technical team verify the pump model and identify a suitable configuration, please provide as much of the following information as possible:
- Existing pump manufacturer and complete model code
- Clear nameplate photographs
- Hydraulic schematic or machine application
- Fluid type and viscosity
- Minimum and maximum operating temperature
- Required displacement or flow
- Continuous and peak pressure
- Pump speed and direction of rotation
- Shaft, flange and port details
- Required quantity and destination country
Review the POOCCA gear pump range, view the internal PGH gear pump, or contact the POOCCA team for model verification.
Frequently Asked Questions
What is the difference between an internal and external gear pump?
An internal gear pump uses a shaft-driven pinion rotating inside an internally toothed ring gear, while an external gear pump uses two externally toothed gears rotating side by side. Internal designs are often selected for smoother, lower-pulsation flow and lower noise. External designs are widely used where compact construction, availability and cost-effective hydraulic power are priorities.
Is an internal gear pump more efficient than an external gear pump?
Not in every operating condition. Efficiency depends on clearances, viscosity, pressure, speed, temperature and wear. Compare the performance data of the specific models at the intended duty point.
Are internal gear pumps quieter than external gear pumps?
Internal gear pumps are often selected for lower-noise hydraulic systems because they can produce smoother, lower-pulsation flow. Installation conditions and pump speed still have a major effect on actual noise.
Which gear pump is better when hydraulic fluid viscosity changes?
Gear type alone does not determine suitability. Compare the permitted fluid type, startup viscosity, operating viscosity, temperature, inlet-pressure range and speed in the technical data for the specific pump model.
Can an internal gear pump replace an external gear pump directly?
Usually not without verification. Displacement, shaft, flange, ports, rotation, rated pressure, speed and installation dimensions must be checked before replacement.
Which gear pump is better for a standard hydraulic power unit?
Either design may be suitable. External gear pumps are widely used for compact and cost-effective hydraulic power units. Internal gear pumps are often considered when lower noise and smoother flow are important.
Conclusion
The main advantage of an internal gear pump over an external gear pump is its ability to provide smooth, low-pulsation and typically quieter flow. The external gear pump remains a practical choice for many compact, cost-sensitive hydraulic systems.
Selection should be based on the complete operating condition rather than a single advantage. Send POOCCA the pump model, fluid, viscosity, flow, pressure, speed, mounting information and application details so the technical team can verify a suitable configuration before quotation.
Post time: Jul-13-2023
