Displacement Range - A key parameter for selecting a suitable hydraulic gear pump
Definition and Importance of Displacement Range in Hydraulic Gear Pump Selection
Definition of Displacement Range:
The displacement of a hydraulic pump refers to the volume of liquid discharged per revolution without leakage, usually expressed in cubic centimeters per revolution (cm³/rev). For an external gear pump, the displacement is the volume of oil delivered by the sealed cavity formed by the two meshing gears per revolution. The displacement range refers to the displacement range that can be provided by this type of pump under different models or designs, covering the flow capacity of small precision pumps to large industrial pumps.
Importance of Displacement Range In The Selection of External Gear Pumps:
Determine flow requirements: The displacement directly determines the theoretical flow of the pump (flow = displacement × speed), which is the basis for meeting the flow requirements of the system. When selecting, you need to select a pump with the appropriate displacement according to the required flow of the system.
Influence on system pressure and efficiency: Pumps of different displacements have different output flows at the same speed, which in turn affects the system pressure stability and energy efficiency performance.
Matching drive equipment and working conditions: The displacement range helps to match the power of the drive motor or engine during selection, and meet the flow and pressure requirements under different working conditions.
Economy and volume considerations: Choose a pump model within the displacement range to avoid over- or under-sized pumps, and optimize costs and equipment volume
How To Optimize Hydraulic System Performance
Displacement and speed jointly determine flow output (flow = displacement × speed), but pressure is mainly determined by system load. The larger the displacement, the higher the pump volume and mechanical strength requirements, and the design pressure level may be higher, but small displacement pumps are often used in actual high-pressure applications to ensure safety and stability.
Excessive speed will increase the centrifugal force of the oil, making it difficult to maintain the seal, causing cavitation and vibration, affecting pressure stability and pump life.
The pressure rating is mainly determined by the structure and sealing performance of the pump, but the displacement range indirectly affects the pressure performance. **Generally, a larger displacement gear pump outputs a larger flow at the same speed, but the pressure rating may be limited due to internal leakage and mechanical stress. The maximum operating pressure of most standard external gear pumps is generally around 140 bar (about 2000 psi), such as the Northern 4000 series pumps, which can withstand pressures up to 2000 psi.
The relationship between displacement and pressure is not linear, and pressure is mainly determined by system resistance and load. **The outlet pressure of a positive displacement gear pump depends on the load resistance of the system, not the displacement of the pump itself. However, the larger the displacement, the higher the pump volume and mechanical strength requirements, and the higher the design pressure rating may be.
When pressure compensation is used in combination with displacement regulation, the displacement range affects the sensitivity and range of pressure control. For example, a pressure-compensated pump adjusts the displacement to maintain the set pressure, and the displacement range determines the pump’s regulation ability and pressure response under different loads.
The speed range and displacement jointly determine the flow output. When the speed is too low, the sealing and efficiency of the pump decrease. External gear pumps are generally suitable for a wide speed range, with a common operating speed of 1000-3600 rpm. Some models can be as low as 5 rpm to meet low flow requirements.
Larger displacement pumps are usually designed to run at medium and low speeds to reduce wear and heat and extend life. Small displacement pumps can adapt to higher speeds to meet high flow requirements.
Too low speed may cause poor sealing and flow pulsation, affecting pressure stability. However, high-quality gear pumps are designed to maintain good sealing at low speeds to ensure pressure output.
Recommend Suitable Models
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Gear Pump Displacement Range (0.1~300 cm³/rev) Guide: How to Select the Right Model for Your Industry
Choosing the wrong displacement in gear pumps can cost you 20%+ efficiency loss (Source: Eaton Hydraulic Handbook), you need to know:
Standard ranges: 0.1~1.0 cm³/rev (medical) to 200~300 cm³/rev (mining).
Top-selling models: Bosch G3 series (5~100 cm³/rev) for industrial hydraulics.
Pressure limits: <15MPa for small pumps, 25MPa+ for heavy-duty (e.g., Rexroth A10VSO).
Displacement Range: 0.1 – 5 cm³/revMedical Equipment - Dental chair lifting mechanisms
Delivers 0.1~1 cm³/rev micro-flow to hydraulic actuators (e.g., robotic arms), enabling precise motion control with minimal pulsation, critical for sterile and quiet medical environments.
Displacement Range: 0.1 – 5 cm³/revLaboratory Instrument - Precision liquid dispenser
Maintains consistent pressure (10~50 bar) with 1~3 cm³/rev displacement, guaranteeing repeatable accuracy (error <±0.5%) in reagent dispensing or mechanical testing.
Displacement Range: 5.0 – 20 cm³/revPlastics Auxiliary Equipment - Injection molding mold cooler
Circulates coolant (20 L/min flow) at 12～18 cm³/rev to stabilize mold temperature (±1°C), while assisting rapid clamping (80 bar pressure).
Displacement Range: 5.0 – 20 cm³/revTextile Machinery - Dyeing vat agitator
Adjusts dye agitation speed (0～50 rpm) at 5～10 cm³/rev, or maintains yarn tension (<±5N variation) to prevent breakage.
Displacement Range: 20～50 cm³/revConstruction Machinery - Excavator travel motor drive
Delivers 25～40 cm³/rev flow at 180～250 bar to power excavator travel motors (speed 0-5 km/h)
Displacement Range: 20～50 cm³/revAgricultural Equipment - Combine harvester header lift
Supplies 30～50 cm³/rev flow at 120～160 bar to rapidly lift harvester headers (<1s response)
Displacement Range: 100～200+ cm³/revEnergy System - Wind turbine pitch control
Maintains 210 bar pitch pressure (±0.5° accuracy) at 100～150 cm³/rev under -30～80°C
Displacement Range: 100～200+ cm³/revHeavy Metallurgy - Continuous caster oscillator drive
Generates 3000～5000 kN shear force with 180～200+ cm³/rev pumps (500～800 L/min), while maintaining 50～200 Hz oscillation (<±0.1mm amplitude error) via PID control.
How To Choose The Displacement Range According To Equipment Requirements
1. Determine System Flow Rate
According to the design flow rate qv (unit L/min) of the equipment hydraulic system,
Combined with the speed n (rpm) of the hydraulic pump, calculate the required displacement V
V=(qv×1000)/n (unit converted to cm³/rev)
For example, if the system requires a flow rate of 50 L/min and the pump speed is 1500 rpm, the displacement is about 33.3 cm³/rev.
Referring to the Bosch Rexroth T series gear pump, the displacement range starts from about 20 cm³/rev, meeting a variety of industrial flow requirements.
2. Consider Operating Pressure and Pressure Rating
The displacement selection should take into account the maximum operating pressure. Under high pressure conditions, the displacement and speed of the pump are usually limited to ensure mechanical strength and sealing performance.
For example, Parker Hannifin PGP series gear pumps have displacements ranging from 0.8 to 70 cm³/rev, and the maximum working pressure is generally 160-280 bar. The larger the displacement, the lower the maximum pressure level may be.
3. Match Pump Speed Range
Displacement and speed jointly determine the flow output. Too low speed may lead to reduced efficiency, and too high speed may cause wear and noise.
When selecting a pump, the displacement within the rated speed range should be selected to ensure stable operation of the system.
4. Consider efficiency and life (Efficiency and Durability)
Volumetric efficiency and mechanical efficiency affect the actual flow and power consumption, and high-efficiency pumps are preferred.
High-displacement pumps are more complex in design, with higher manufacturing and maintenance costs, and need to be considered comprehensively based on the economic efficiency of the equipment.
5. Refer to authoritative product parameters and selection tables (Use Authoritative Product Data)
Use the selection manuals and technical parameter tables provided by manufacturers, such as Bosch Rexroth, Parker, Vanke, etc., and select the most matching displacement model based on the equipment conditions.
For example, Bosch Rexroth provides detailed displacement, pressure, speed and torque limit data to help with accurate model selection.
FAQs
Answer: The displacement range of an external gear pump usually ranges from 0.1 cm³/rev to about 200 cm³/rev. Taking the ZPDA series as an example, the displacement range is 0.1~26.0 cm³/rev, which is suitable for high-precision metering; while industrial gear pumps such as the Parker PGP series can reach a displacement of more than 70 cm³/rev, meeting the needs of medium and large equipment.
Answer: The displacement selection needs to be calculated based on the required flow rate and pump speed of the system, displacement = flow rate (L/min) × 1000/speed (rpm). At the same time, the working pressure and efficiency must be considered to avoid excessive displacement resulting in increased mechanical load, or too small to meet the flow requirements. Authoritative brands such as Bosch Rexroth provide detailed selection manuals to assist decision-making.
Answer: The larger the displacement, the higher the pump volume and mechanical strength requirements. Usually, the maximum pressure level of high-displacement pumps is relatively low, and the speed is limited to prevent overheating and wear. High-pressure pumps are mostly designed with small and medium displacements and low speeds to ensure life and reliability.
Answer: Small-displacement gear pumps of 0.1~5 cm³/rev are widely used in medical equipment, laboratory instruments, precision metering and lubrication systems, providing stable low-pulsation flow, achieving precise liquid delivery and mechanical motion control, such as the ZPDA series.
Answer: Gear pumps with a displacement of more than 90 cm³/rev are mostly used in heavy machinery, construction equipment, ship hydraulics and mining machinery to meet high flow and high pressure requirements, and the design emphasizes mechanical strength and durability.
Answer: The displacement calculation formula is: q=2πrKZBm2, where Z is the number of teeth, B is the tooth width, m is the module, and K is the displacement compensation coefficient (1.06~1.115). It can also be simplified as q=6.66ZBm2 for estimation.
Answer: Reasonable matching of displacement and system flow can improve volumetric efficiency and mechanical efficiency, avoid leakage and increased energy consumption due to excessive displacement, or insufficient flow due to too small displacement, affecting system stability and life.
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