Mechanical power transmission: Efficiency and losses
Near-perfect gears, but air systems that waste most of their power
What this tab covers How much energy is lost while it moves and while it waits in storage or transit, and how much energy the transport itself consumes, in per cent.Rigid mechanical links are very efficient over short distances: 95 to 99% for gears and belts. Fluid systems are far worse end to end: about 22% on average for US fluid power and only 12 to 17% for industrial compressed air, with leaks alone wasting 20 to 30% of compressor output in poorly maintained plants.
Chart: Efficiency ranges
Lost in transit Whole chainLosses by measure
| Measure | Range | Type | What is measured |
|---|---|---|---|
| Gear mesh, best-designed high-power gears | 98 to 99%6 | Lost in transit | Share of input power delivered per gear stage |
| V-belt, new, against synchronous belt | 95 to 98%1 | Lost in transit | Peak V-belt efficiency of 95% or more at installation; synchronous belt about 98% across loads |
| V-belt slip with poor tensioning | 5%1 | Lost in transit | Efficiency that can be lost over time if belts are not retensioned |
| Hydraulic systems, mobile against industrial | 21 to 50%2 | Whole chain | Average whole-system efficiency, input energy to useful work, US estimate |
| Industrial pneumatic (compressed-air) systems | 12 to 17%2 | Whole chain | Whole-system efficiency including the compressor; downstream of the compressor 23 to 30% |
| Compressed-air leaks | 20 to 30%3 | Lost in transit | Share of compressor output lost to leaks in a poorly maintained plant; under 10% is the good-practice target |
Holding periods and inventory
| Measure | Value |
|---|---|
| Compressed-air receivers and pipes | Leaks continue whenever the system is pressurised; leakage is measured by timing how fast pressure falls from operating level to about half3 |
| London hydraulic network throughput (1930) | About 33 million gallons of water a week (roughly 1.7 billion a year, calculated) serving about 8,000 machines26 |
US fluid power systems use an estimated 2.0 to 2.9 quads of energy a year (2008 data), about 2 to 3% of national energy use (calculated against about 100 quads), at an average efficiency of about 22%. Raising that average to 27% through best practice could save about 0.4 quads a year, and to 37% through research about 0.8 quads. A later NREL study (2017) put mobile off-road fluid power alone at 0.36 to 1.8 quads, so the older estimate may be low.
Distance matters most for fluids: friction in pipes and leaks grow with network length, which is one reason the city-scale hydraulic and compressed-air networks of London and Paris closed once electricity could reach every building.
Sources
- Replace V-belts with notched or synchronous belt drives (Motor Systems Tip Sheet #5) US Department of Energy, Advanced Manufacturing Office, 2012
- Estimating the Impact (Energy, Emissions and Economics) of the U.S. Fluid Power Industry (ORNL/TM-2011/14), Love, Lanke and Alles Oak Ridge National Laboratory, 2012
- Compressed Air System Leaks (Improving Compressed Air System Performance, Fact Sheet #7, Rev. 1) Compressed Air Challenge, 2026
- Using the Box-Behnken response surface method to study parametric influence to improve the efficiency of helical gears (Machines 9(11), 264) MDPI, 2021
- London Hydraulic Power Co Grace's Guide to British Industrial History, 2025