The UK's energy use per unit of GDP has fallen by about 52% since 1980. GDP more than doubled, while primary energy consumption rose by only around 2%, according to the UK government's energy-efficiency statistical summary. That national improvement can still conceal substantial waste on a factory floor, where a hydraulic power pack may draw energy without producing useful actuator work.
Judge system efficiency at the machine boundary, not from a pump catalogue figure or a national trend. Measure how much electrical input becomes controlled actuator movement, useful force, and productive cycle time. Include the complete duty cycle, including pressure holding, unloaded running, throttling, and idle periods.
What System Efficiency Really Means
A hydraulic system can sit inside a UK economy whose industrial energy intensity fell by 54% since 1980, yet still run hot, throttle unnecessarily, or draw power without producing useful work. The official statistical summary records an average annual fall of 1.6% during the 1990s and 2.9% from 2000 onwards. Those national figures describe broad productivity, not the performance of a specific press, loader, lift table, or conveyor power unit.
At machine level, define system efficiency as:
Useful hydraulic work at the actuator ÷ electrical energy drawn at the motor terminals × 100
The boundary must include a defined duty cycle. Cylinder movement under load, pressure holding, motor idling, and pump operation against an unloaded circuit each consume energy differently. A national improvement can therefore coexist with significant waste at an individual machine.
Separate the three efficiency measures
Volumetric efficiency compares actual pump delivery with theoretical displacement. It indicates internal leakage, which generally rises with pressure, temperature, and wear. The basic relationship is actual flow divided by theoretical flow at the operating pressure.
Mechanical efficiency covers friction in the pump and drive train. Bearing condition, shaft seals, coupling alignment, oil viscosity, and pump turning torque all affect the result.
Overall efficiency includes the motor, coupling, pump, valves, pipework, actuator, leakage paths, and heat rejection. This is the figure that matters when electricity or fuel costs are tied to machine output.
Use the right baseline
Keep two measurements separate:
- Instantaneous efficiency applies to one operating point, such as a fixed flow and pressure.
- Cycle-averaged efficiency weights each operating phase by its duration, including idle and standby periods.
A datasheet figure taken at a selected pressure and speed does not predict average performance across a variable duty cycle. For a useful baseline, hydraulic performance benchmarking should record actual load, flow, pressure, temperature, and power during representative work, rather than relying on no-load observations.
Efficiency becomes meaningful when the complete machine delivers the required service with less wasted input. The House of Commons Library briefing provides a separate domestic example, reporting that the average energy-efficiency rating of UK homes rose from 51.4 in 2008 to 67.2 in 2022, while the share rated band C or higher increased from 10% to 52%. The same measurement principle applies to hydraulics: assess the useful result against all energy drawn across the duty cycle.
Why Component Efficiency Is Not System Efficiency
A pump can show 80% to 90% efficiency at its test point and still form part of a circuit whose overall efficiency is only 21% to 22%. Pressure drops, throttling, leakage, friction, and heat rejection occur after the pump and consume energy before the machine produces useful output. The hydraulic efficiency discussion explains why the system boundary matters.
The distinction becomes clear with a simple example. If five stages each operate at 90% efficiency:
0.90 × 0.90 × 0.90 × 0.90 × 0.90 = approximately 59%
This is an illustration of compounded losses, not a prediction for every machine. A pump, valve group, pipework, actuator, and mechanical output stage may each appear acceptable in isolation, yet the combined result can be much lower.
| Stage | Component Efficiency | Cumulative Efficiency |
|---|---|---|
| Pump | 90% | 90% |
| Valve group | 90% | 81% |
| Pipework and fittings | 90% | 73% |
| Actuator | 90% | 66% |
| Mechanical output stage | 90% | Approximately 59% |
Define the boundary before changing parts
Pump-shaft efficiency covers the conversion from shaft input to hydraulic output at the pump ports. Cylinder-rod efficiency measures what reaches the rod after valves, hoses, fittings, leakage, and pressure losses. Electrical system efficiency starts at the motor terminals and includes the drive, motor, coupling, pump, and hydraulic circuit.
Keep volumetric efficiency separate from overall efficiency. This explanation of volumetric efficiency helps distinguish delivered flow from the wider energy balance.
These measurements answer different questions. Replacing a pump because its shaft efficiency is below expectation will not necessarily reduce machine energy use if a throttling valve, restrictive fitting, or undersized return filter creates the dominant loss. A national efficiency improvement can therefore coexist with substantial waste in an individual power pack. Aggregate performance does not reveal where a particular machine loses energy.
Why the actuator figure can be surprisingly low
Throttling converts pressure potential into heat. Leakage diverts oil from the useful work path, heat exchangers remove energy already supplied by the motor, and friction adds loss at moving interfaces. The result is useful hydraulic efficiency below 25% in some presses and power units, even when individual components have strong catalogue ratings.
The commonly cited whole-system range of 21% to 22% provides context, not a pass or fail target for every installation. The practical task is to identify the loss that dominates the actual duty cycle.
Practical rule: State whether the measurement starts at the motor terminals, pump shaft, pump ports, or actuator output before approving an efficiency upgrade.
The changes that usually affect the electricity meter are reduced throttling, pump displacement matched to demand, and testing under real load. A component upgrade that leaves operating pressure, flow, and control behaviour unchanged may improve a datasheet figure without improving machine efficiency.
The Main Loss Mechanisms in Hydraulic Circuits
Hydraulic losses usually fall into a small number of categories, but their importance changes with the duty cycle. A press holding pressure at standstill behaves very differently from a mobile machine completing rapid lift, steer, and auxiliary functions.
Internal leakage and volumetric loss
Pump leakage increases as pressure and wear rise. The result is less actual flow for a given displacement, more heat in the oil, and longer actuator response. Measure theoretical flow against actual flow at the operating pressure, then compare the result with oil temperature and leakage observations.
A worn pump isn't always the first part to replace. If the machine spends most of its time at low demand, a control strategy that keeps the pump producing unnecessary flow may waste more energy than the pump's internal leakage.
Throttling and pressure drop
Proportional and pressure-compensated valves can offer excellent control, but a pressure difference across a valve represents energy converted into heat. Pressure drops also develop through pipework, fittings, filters, quick-release couplings, and undersized passages.
Check pressure at the pump outlet and again near the actuator during the same load step. A large difference points towards circuit restriction, while unstable pressure can indicate control interaction, contamination, incorrect compensation, or pump cavitation. The guide to what causes pump cavitation is useful when noise, erratic flow, or damaged pump surfaces suggest an inlet-side problem.
Mechanical and parasitic losses
Actuator seals, bearings, couplings, shaft seals, and mechanical linkages all consume power. Case-drain and pilot circuits also impose parasitic flow requirements, even when they aren't producing the main movement.
Heat is the visible symptom. Record stabilised reservoir temperature, ambient temperature, and the machine phase during which heat rises. A holding press may waste energy through leakage and relief or valve throttling, whereas a high-cycle mobile machine may lose more through poor displacement matching and inefficient accumulator charging.
For teams responsible for quoting or repair planning, operational delay can also create hidden cost. The resource on quoting delays cost work provides useful commercial context, because a technically sound efficiency project still loses value if diagnosis, parts selection, and intervention planning move too slowly.
The correct order is to profile the load first, identify the dominant loss, and then select the intervention. Don't begin with a pump replacement just because the pump is the most recognisable component.
Measuring and Modelling Real-World Efficiency
A credible efficiency assessment needs measurements taken at the same time. Pressure alone won't show flow loss, and temperature alone won't identify whether the cause is throttling, leakage, or mechanical friction.
Instrument the power unit and actuator
Fit a flow meter in the pump delivery line, a pressure transducer close to the actuator, and a temperature probe in the reservoir. Add electrical power measurement at the motor feeder where practical. Pressure gauges remain valuable for quick checks, but logged transducers reveal instability and short load phases that a technician may miss while watching a dial.
Record the machine through a complete representative cycle. Separate loaded movement, unloaded return, pressure holding, standby, and start-up phases. The UK government's pumping-station guidance supports this system-level approach, evaluating efficiency through annual savings and cost reduction while treating flow, pressure, duty cycle, and control strategy as connected variables. The engineering report on pumping-station efficiency provides useful verification principles for mature fluid systems.
Calculate the measures consistently
Volumetric efficiency is actual flow divided by theoretical flow at defined speed, pressure, and temperature. Mechanical efficiency requires torque and the pressure differential across the pump, while overall efficiency compares hydraulic power delivered at the actuator with electrical power drawn at the motor terminals.
| Metric | Formula | Instrumentation | Typical bench target |
|---|---|---|---|
| Volumetric efficiency | Actual flow ÷ theoretical flow | Flow meter, pressure transducer, speed measurement | Compare with the manufacturer’s stated operating point |
| Mechanical efficiency | Hydraulic pump power ÷ shaft power | Pressure and flow measurement, torque meter, speed measurement | Validate against the pump test condition |
| Overall system efficiency | Hydraulic power out ÷ electrical power in | Flow meter, actuator pressure, motor power meter | Establish a measured duty-cycle baseline |
The table deliberately uses a bench target as a comparison point, not a universal pass mark. A laboratory test cycle can be repeatable without representing the machine's real loading.
Warm the system and log the duty cycle
Run the power unit until oil temperature stabilises before comparing readings. Log flow, pressure, temperature, motor power, and cycle state at an interval that captures the shortest meaningful load phase. The exact logging interval should suit the machine response, rather than being selected for convenience.
A simple kilowatt-hour meter on the motor feeder can reveal more about an existing power pack than an isolated calibrated rig if the objective is to understand actual operating cost. Differential pressure measurement can also help locate restrictions and quantify filter or valve behaviour. For background on the benefits of differential pressure transmitters, use the technical guide from Axis Meter Solutions.
Proven Hydraulics-Specific Strategies
The control strategy should follow the machine's duty cycle. Mobile agricultural equipment may shift rapidly between flow and pressure demands, while a fixed industrial press can repeat a predictable sequence and spend extended periods holding pressure. The same component choice can therefore produce different results on each machine.
| Strategy | Best application | Efficiency gain | Capital cost band |
|---|---|---|---|
| Throttling control | Simple circuits with modest variation | Limited, because surplus pressure becomes heat | Low |
| Load-sensing control | Mobile machinery with changing actuator demand | Strong where flow demand varies substantially | Medium |
| Inverter-driven variable-speed pump | Fixed industrial machines with variable cycle demand | Strong where standby and low-load periods are significant | Medium to high |
Match displacement to demand
A fixed-displacement pump is durable and economical, but it delivers flow whenever the shaft turns. If a valve rejects surplus flow, the motor still supplies the pressure required to create heat across that restriction. A variable-displacement or load-sensing arrangement reduces delivery as demand falls. The trade-off is greater control complexity, more commissioning work, and a need for correct standby-pressure adjustment.
An inverter-driven pump suits a fixed press with long low-demand periods. It can reduce motor speed rather than forcing the pump to circulate full flow, but the package brings higher capital cost, motor and drive compatibility checks, electromagnetic compatibility requirements, and commissioning time. It is less attractive on a mobile machine where engine speed, packaging, shock loading, and field serviceability may outweigh steady electrical optimisation.
Reduce peak demand without creating a new problem
An accumulator can cover short demand peaks, allowing the pump to be sized for a practical average rather than the highest instantaneous flow. Selection must account for pressure range, gas pre-charge, temperature, cycle frequency, safety requirements, and available volume. Poor sizing can increase charging losses or make control unstable.
Filtration affects efficiency through wear, leakage, and restriction. Specify the filter element's required beta performance, pressure drop at actual flow, bypass behaviour, and maintenance interval. A finer element that blocks quickly, or creates excessive pressure loss, shifts the energy penalty from contamination to filtration.
Treat temperature as a design parameter
Reservoir volume, heat-exchanger capacity, oil viscosity, ambient conditions, and duty cycle interact. Stabilise oil temperature before comparing modifications, then repeat the same load steps so the result reflects the intervention rather than changing thermal conditions. Keep the system within the fluid and component manufacturer's temperature limits instead of applying a universal threshold.
At machine level, these measures can expose waste that national efficiency figures conceal. A country may report gradual improvement while individual power packs continue to lose energy through throttling, leakage, poor control settings, or unnecessary heat rejection. Component selection must therefore be tied to the measured duty, not to a national average or a catalogue efficiency value.
Build the business case around capital cost, annual energy saving, maintenance impact, and payback in months. A seal replacement may repay quickly, while an inverter or bespoke power pack needs a stronger load profile and a defensible operating-cost model. Throughput also matters. The practical discussion in the Doczen guide to throughput gains is relevant when an efficiency change improves cycle consistency as well as energy use.
How to Build a Defensible Case Study in GBP
A useful hydraulic efficiency case study starts with four records: the baseline, the intervention, the measurement boundary, and the post-change verification. Record the machine's operating conditions in both periods, because a change in workload, operator behaviour, production rate, or temperature can outweigh the component modification.
The loader and press-cell examples below are templates to populate with measured results. They connect national efficiency narratives with machine-level evidence. A country may report improving energy performance while an individual power pack still wastes energy through standby flow, throttling, leakage, or poor control settings.
Mobile machinery study template
For a loader, record fuel use, engine hours, hydraulic pressure, pump flow, lift and auxiliary duty, ambient conditions, and the proportion of work spent travelling or waiting. A load-sensing retrofit may reduce unnecessary pump flow. An accumulator change may support short peaks. The outcome depends on calibration, operator behaviour, engine loading, and the actual harvest duty.
Include pump or control hardware, accumulator, pipework, installation, commissioning, and downtime in the intervention cost. Calculate payback from measured fuel consumption under matched work conditions, compared with the pre-change baseline.
Industrial press study template
For a press cell, log motor-feeder energy, cycle count, pressure-holding time, unloaded time, cycle duration, oil temperature, and production output. A variable-speed pump and proportional valves may reduce standby and throttling losses, but they add drive, control, tuning, and maintenance requirements that belong in the evaluation.
| Case | Baseline | Intervention cost | Annual saving | Payback |
|---|---|---|---|---|
| Mobile agricultural loader | Measure under a defined representative duty cycle | Calculate from quoted hardware and installation | Calculate from verified fuel reduction | Intervention cost ÷ annual saving |
| Industrial press cell | Measure at the motor feeder across normal production | Calculate from the power-pack and control quotation | Calculate from verified electricity reduction | Intervention cost ÷ annual saving |
Use the same duty definition before and after the change. State whether the boundary covers fuel or electricity input only, and whether production output is unchanged. A lower energy reading has limited value if the machine completes fewer cycles or handles less load.
This format gives a maintenance manager enough information to challenge assumptions, repeat the test, and decide whether the proposed change warrants capital approval.
A payback claim is only as reliable as the operating baseline behind it.
Your System Efficiency Action Checklist
Start with an audit that produces useful information before any component is ordered. A maintenance engineer should be able to walk the system, identify obvious losses, and establish whether the main problem is flow, pressure, temperature, leakage, control, or idle operation.
First pass through the machine
- Audit: Check hose routing, fittings, couplings, seals, reservoir condition, pump noise, valve blocks, and visible leakage.
- Measure: Confirm that pressure gauges read correctly, then connect flow, pressure, temperature, and electrical power instrumentation where available.
- Record: Log a complete representative duty cycle, including loaded movement, unloaded return, holding, standby, and start-up.
The first measurements should be repeatable. Stabilise oil temperature, use the same load steps, and record the machine state with every reading. If you can't describe the duty cycle, you don't yet have an efficiency baseline.
Prioritise the intervention
Quick wins include repairing external leaks, replacing damaged seals, rerouting restrictive hose assemblies, cleaning coolers, and replacing a filter element when pressure drop shows restriction. These actions are relatively contained and can often be validated without redesigning the circuit.
Medium-term work includes checking pump displacement against actual demand, reviewing relief settings, assessing valve throttling, auditing heat exchanger performance, and considering load-sensing or variable-speed control. A bespoke power pack can make sense where the duty cycle is highly asymmetric and an off-the-shelf unit spends much of its operating time outside its efficient region.
Use trigger values carefully. A 15°C rise in reservoir temperature above ambient under no-load should prompt investigation, but it isn't a universal failure limit. Likewise, a difference exceeding 10% between pump output and actuator demand at working pressure justifies checking leakage, measurement accuracy, valve bypass, and sizing before condemning a component.
The reporting sheet should contain:
- Baseline: Flow, pressure, motor power, oil temperature, cycle time, load phase, and production condition.
- Intervention: Parts changed, control settings, installation date, downtime, and commissioning readings.
- Verification: Repeat measurements at the same operating points and record energy, temperature, leakage, response, and cycle consistency.
- Decision: State the dominant loss, recommended action, estimated capital cost, expected annual saving, and calculated payback in months.
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MA Hydraulics Ltd can help assess hydraulic circuits, select matched pumps, valves, filters, motors, couplings and manifolds, and assemble Hydronit mini power packs or bespoke industrial power packs up to 11 kilowatts. Visit MA Hydraulics Ltd to discuss a measured system-efficiency improvement, or phone 01724 279508 today, or send us a message with your application details.
