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.
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:
Both are essential when evaluating hydraulic pump and motor efficiency, especially in high-load applications where flow rate and pressure drop matter.
Volumetric efficiency refers to how much of the theoretical flow a pump actually delivers at a given pressure.
Volumetric Efficiency = (Actual Flow ÷ Theoretical Flow) × 100
For example:
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.
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:
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.
To get the overall efficiency, you need:
Overall Efficiency = Hydraulic Power Output / Mechanical Power Input
Where:
You can quantify the pump and compare actual efficiency against native efficiency specs from the manufacturer.
Even the most efficient pump will degrade over time. Here's what typically causes it:
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.
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.
Pump flow and flow and pressure must be matched to system demands. Oversized pumps generate heat; undersized pumps cause starvation.
Key things to consider:
Here's how to increase efficiency - without needing to replace the entire pump:
These errors show up a lot in field maintenance logs:
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.
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
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