Updated: September 2025
Introduction
Torque is fundamental in how air motors perform across applications – from precision tool assembly on a shop floor to tightening bolts in harsh industrial environments. Though torque figures may appear straightforward, they vary significantly across manufacturers and setups, leading to confusion. This article demystifies the key torque terms – starting, working, and maximum torque – explaining how each influences practical performance and selection decisions.
Torque Value Types Explained
1. Working Torque
This is the torque a motor consistently delivers during normal operation. It reflects real-world performance under load and is what engineers rely on when designing or sizing systems.
2. Maximum Torque
Also called peak or theoretical torque, this value represents the upper limit a motor could deliver in ideal, controlled conditions. It often looks impressive on paper but may not be sustainable in actual use due to friction, material limitations, or environmental factors.
3. Starting Torque
This is the torque available when the motor begins turning from rest. It is critical for overcoming initial resistance – like static friction or inertia – and is generally around 75% of stall torque. If the load’s break-away torque exceeds this, the motor won’t start.
Stall Torque: The Reality Check
Stall Torque is the maximum torque the motor produces at the point of stopping or stalling. While typically not listed in catalogues, a useful rule of thumb is that stall torque equals about twice the maximum power torque – for example, a 10 Nm power torque roughly converts to a 20 Nm stall torque.
It’s also worth to stress how fast the motor stalls affects this torque: faster stops yield higher stall torque due to rotor inertia.
Why These Values Matter
Understanding and distinguishing these torque measurements is essential for motor selection and application success:
Avoid Misapplication: Relying solely on maximum torque can lead to system mismatches – choose based on working torque for dependable performance.
Ensure Startup Capability: Always size the motor so starting torque exceeds the break-away load.
Build Durability: Avoid pushing motors to stall torque in prolonged operations to prevent wear – reserve that headroom for short bursts only.
Common Pitfalls in Torque Comparison
Lack of Standardization: Different brands calculate and present torque values differently – without standard units, like Nm, or uniform testing protocols – so direct comparisons are tricky.
Overemphasis on Theoretical Maxime: Numbers like “maximum torque” look good, but applications require predictable, sustainable performance.
Ignoring Environmental Impacts: Air temperature, humidity, or pressure loss in the supply network can reduce actual torque output versus specifications.
Testing & Real-World Validation
There’s no substitute for hands-on testing. Field trials help you see how torque values translate into real-world performance, particularly under varying loads and conditions. Chicago Pneumatic’s experts advise:
“Torque value shouldn’t be your only consideration… timing, hose length, air pressure… real-life tests matter most.”
Quick Summary Table
| Torque Type | Definition | Why It Matters |
|---|---|---|
| Working Torque | Continuous operational torque | Determines real-case motor sizing and function |
| Maximum Torque | Theoretical peak in ideal scenario | Can mislead if not properly contextualized |
| Starting Torque | Torque at system startup | Must exceed load break-away for proper start |
| Stall Torque | Torque when motor stops or stalls | Useful for burst loads—shouldn’t be continuous |
Conclusion
Differentiating between torque values is vital for choosing and operating air motors reliably. Focus on working torque for baseline performance, verify starting torque can overcome system resistance, and reserve stall torque headroom for rare or emergency scenarios. Most importantly – test in context to avoid surprises in operation. Want help applying these concepts to a specific motor or project? Just say the word – I’d be happy to assist!
For further insights and detailed technical information, consult the Pocket Guide to Air Motors by Atlas Copco or Contact us directly.
