Hydraulic Pump Efficiency: How to Measure, Calculate & Improve Performance

If you're running a hydraulic system and starting to notice sluggish performance, extra heat, or using more energy than usual - your hydraulic pump efficiency is likely on the decline. Whether it’s a gear pump, piston pump, or variable displacement pump, every drop in efficiency impacts output, energy use, and long-term reliability.

In this guide, we’ll explain how to calculate volumetric efficiency, identify what causes losses, and show you how to get the most from your pump and motor setup-whether it's a mobile system or an industrial unit.

What Is Hydraulic Pump Efficiency?

Hydraulic pumps convert mechanical energy into hydraulic energy by moving hydraulic fluid under pressure. Pump efficiency is a measure of how effectively that conversion happens. There are two main types:

• Volumetric efficiency - how well the pump maintains flow
• Overall efficiency - a combined measure that includes mechanical losses

Both are essential when evaluating hydraulic pump and motor efficiency, especially in high-load applications where flow rate and pressure drop matter.

Volumetric Efficiency: How It Works

Volumetric efficiency refers to how much of the theoretical flow a pump actually delivers at a given pressure.

Formula

Volumetric Efficiency = (Actual Flow ÷ Theoretical Flow) × 100

For example:

• Pump has a displacement of 80cc/rev
• Speed: 1500 rpm
• Theoretical flow = 120 L/min
• Measured using a flow meter: 102 L/min
• Volumetric efficiency = 85%

This drop in efficiency is often caused by internal leakage due to worn seals or increased clearances, especially in older piston pumps and gear pumps.

Calculating the Volumetric Efficiency of a Variable Displacement Pump

With a variable displacement pump, it's not just about wear - system design, control strategy, and fluid viscosity all affect efficiency.

When displacement is altered, so is the flow delivered by the pump. To calculate efficiency:

1. Identify actual flow at current displacement
2. Confirm theoretical flow from specs
3. Apply the standard formula

If theoretical flow is 100 and you measure actual flow of 90, your pump's efficiency is 90%. A sharp drop in flow may indicate internal leakage and fluid breakdown.

How to Calculate Hydraulic Pump Efficiency

To get the overall efficiency, you need:

• Flow meter to measure actual output
• Pressure gauge for system pressure
• Drive power reading in kW

Formula:

Overall Efficiency = Hydraulic Power Output / Mechanical Power Input

Where:

• Hydraulic power = (Flow × Pressure) ÷ 600
• Mechanical input = shaft power supplied

You can quantify the pump and compare actual efficiency against native efficiency specs from the manufacturer.

What Affects a Pump’s Efficiency Over Time?

Even the most efficient pump will degrade over time. Here's what typically causes it:

• Increase in internal leakage
• Worn bearings affecting torque
• Contaminated hydraulic fluid
• Fluid too thin or too thick (wrong viscosity)
• Pumps run too close to relief settings

This is why tracking efficiency over time in a condition-based maintenance environment makes sense. It helps to identify bearing life or deteriorating efficiency issues before failure.

Hydraulic Pumps and Motors: Efficiency Link

Every hydraulic system component contributes to efficiency - but the pump or motor is usually the most significant player.

If the pump can convert energy with volumetric efficiency of 92%, but the motor efficiency ratings are poor, you're losing power in the system.

This is especially critical in closed-loop systems where hydraulic energy is turned back into mechanical work.

Hydraulic Pump Types: Efficiency Differences

Piston Pumps and Motors

• Higher pressure rating
• Better efficiency rating (typically 90-95%)
• Sensitive to internal leakage from wear

External Gear Pumps

• Simpler, lower cost
• Efficiency typically 80-88%
• A system with gear pumps needs good filtration to prevent wear

Bent Axis Piston Pump

• Used in high-demand mobile or industrial systems
• Compact with high power density
• High efficiency of a variable displacement pump if correctly tuned

How System Design Impacts Pump Efficiency

Pump flow and flow and pressure must be matched to system demands. Oversized pumps generate heat; undersized pumps cause starvation.

Key things to consider:

• Match the required drive power to the application
• Avoid unnecessary pressure drop across valves
• Monitor flow delivered by a pump regularly
• Account for fluid viscosity changes in hot or cold weather
• Don’t let motors require a bigger heat exchanger due to inefficiency upstream

How to Improve Hydraulic Pump Efficiency

Here's how to increase efficiency - without needing to replace the entire pump:

• Monitor pump at a given pressure to detect performance drop
• Use flow meters and gauges during service intervals
• Choose the right hydraulic fluid with proper viscosity index
• Check for internal leakage in piston pumps and motors
• Apply condition-based maintenance
• Track actual flow vs theoretical flow over time

Common Mistakes That Kill Pump Efficiency

These errors show up a lot in field maintenance logs:

• Running a pump had an actual flow far below spec without checking why
• Using the wrong oil and causing efficiency of 85 to drop to 70s
• Oversizing the pump - drive power for an external gear pump too high
• Failing to test whether the pump was delivering flow consistently
• Assuming that motor efficiency ratings is essential only for electric motors

FAQs: Understanding Hydraulic Pump Efficiency

What does it mean if a pump has a volumetric efficiency below 85%?
Internal wear is likely a result of leakage or deteriorating hydraulic fluid condition-time to inspect.

How do I calculate the efficiency of a hydraulic pump?
Use actual vs theoretical flow, or divide hydraulic output power by shaft input power.

What’s a typical efficiency rating for a gear pump?
Usually between 80-88%. Higher when new, but drops faster than a piston pump.

What happens to efficiency in high-pressure systems?
If system pressure is too high, internal leakage increases. Efficiency drops, and more heat is generated.

Conclusion

Understanding hydraulic pump efficiency is the difference between running a smooth, energy-smart system and increased operational expenses as a result of poor design and late maintenance. Whether it’s calculating the volumetric efficiency of a variable unit or working out if your pump at a given pressure is still delivering, it pays to stay ahead of the game.

Efficiency isn’t just a number - it’s a clear window into the health of your entire hydraulic system.

Posted by admin in category Hydraulic Pumps Advice on Tuesday, 16th December 2025