Load capacity tells you how much force a linear actuator can push, pull, or hold without failing. It breaks down into two main types: static load, which is what it can hold when stopped, and dynamic load, which is what it can move while running. Understanding both is critical for selecting the right actuator and avoiding premature failure.
What Is Load Capacity?
Load capacity is basically the actuator’s strength rating. It tells you the maximum force the actuator can handle safely, whether that’s moving something or just holding it in place. Manufacturers measure this in pounds force (lbf) or Newtons (N), and it’s one of the first specs you’ll see on any datasheet.
But load capacity isn’t just one number. There are different types of loads working on an actuator, and each one affects performance differently.
Static vs Dynamic Load Capacity
These are the two main categories, and they measure completely different things.
Static Load Capacity
Static load is what the actuator can hold when it’s not moving. When the motor shuts off, how much weight can the actuator support without backdriving, which is when the load forces the actuator to move backward on its own?
This matters for applications like adjustable desks, lifting platforms, or anything where you need to hold a load steady. Static capacity is usually higher than dynamic capacity because holding something stationary puts less stress on internal components.
Dynamic Load Capacity
Dynamic load is the force an actuator can push or pull while it’s actually moving. This is your working load, the force you’re applying during extension or retraction. It’s typically lower than static capacity because moving generates heat, wears components faster, and requires the motor to continuously overcome friction and inertia.
When you’re sizing an actuator, dynamic load is usually the limiting factor because that’s when the actuator is working hardest.
Other Types of Loads You Need to Know
Beyond static and dynamic, there are other load types that can affect your actuator’s performance and lifespan.
Push vs Pull Loads
Some actuators have different ratings for pushing versus pulling. Compression forces and tension forces stress internal components differently. Always verify that the actuator handles whichever load type dominates in your setup.
Radial and Side Loads
Radial loads, also called side loads, are forces applied perpendicular to the actuator’s rod. These should always be avoided because linear actuators don’t have internal guide systems to handle sideways pressure. Side loading causes increased internal friction, rapid wear on bearings and seals, and premature failure.
If your application can’t avoid side loading, you need to add external slide rails or guide systems to protect the actuator from lateral forces.
Shock Loads
Shock loads are sudden, momentary spikes in force that happen unexpectedly. Common causes include rough terrain for mobile equipment, sudden stops or starts, or impact events. These spikes can dramatically exceed your normal operating load and cause immediate damage if the actuator isn’t designed to handle them.
Helping Loads
A helping load is when the force you’re moving actually assists the actuator’s motion instead of resisting it. For example, if you’re extending an actuator upward and something is pulling on it in the same direction, that’s a helping load during extension. These situations can allow you to use a smaller actuator, but you still need to make sure the actuator can control the movement.
What Determines Load Capacity?
Load capacity comes from the actuator’s internal design and the components used to build it.
Drive Mechanism
The screw type has a huge impact on both static and dynamic capacity:
- Acme screws have high friction, which gives them excellent static load capacity and natural self locking when the motor stops.
- Ball screws use rolling elements with very low friction and high efficiency. The downside is poor static load capacity because they can backdrive easily.
For industrial valve applications, worm gear and worm mechanisms provide excellent static holding capacity and natural self locking. This design keeps valves secure even when power is lost.
Thread Pitch
Thread pitch is how far the screw advances with each rotation. Tighter threads give you more force but slower speed. Coarser threads give you faster movement but less force. This is a fundamental trade off: force and speed work against each other.
Motor and Gearing
Bigger motors provide more torque, which translates to higher load capacity. Gear ratios amplify motor torque, so higher gear ratios increase force output. But higher gearing reduces speed. Robust gears made from hardened steel handle higher loads and last longer than cheaper alternatives.
Construction Materials
The materials used for gears, bearings, shafts, and housing all affect total capacity and durability. Industrial grade actuators use hardened steel components and robust housings. Die cast aluminum housings with corrosion resistant finishes provide good protection in harsh environments while keeping weight reasonable.
Selecting the Right Load Capacity
Getting load capacity right during selection prevents failures and extends actuator life.
Apply Safety Factors
Never size an actuator to operate at its maximum rated capacity. Always include a safety factor, typically 1.5 to 2 times your actual required load. This buffer accounts for load variations, calculation errors, degradation over time, and unexpected conditions.
Consider Duty Cycle
Duty cycle is the ratio of on time to total cycle time. Operating at high loads generates more heat, which affects how often you can run the actuator without overheating. Heavy loads and high duty cycles don’t mix well unless you have an actuator designed for continuous operation.
If you need continuous or near continuous operation, look for actuators that offer continuous operation modes. Our AOX-L Series provides options for on off, modulating, and continuous operation depending on your duty cycle requirements.
Account for All Load Types
Don’t just size for the obvious pushing or pulling force. Think about whether you’re pushing, pulling, or both, potential shock loads, any unavoidable side loading, and helping loads that might allow downsizing.
Match Thrust Capacity to Application Demands
Once you’ve calculated your load requirements with proper safety factors, you need to find an actuator that delivers the thrust you need. For valve automation in industrial settings, thrust requirements typically range from a few thousand Newtons for smaller valves up to 40000N or more for heavy duty applications.
Standard Industrial Applications
For most industrial valve control where you need thrust in the 3000N to 30000N range, standard linear actuators cover gate valves, globe valves, and control valves across petroleum, chemical, water treatment, and power generation.
System Integration Requirements
When your application requires automated control or remote monitoring, look for models with built in communication capabilities. The AOX-L Intelligent actuator handles the same thrust range as standard models but adds protocols like Modbus, Profibus, and Hart for connecting into facility wide control networks.
Hazardous Locations and Heavy Duty Needs
For locations where explosion risks exist, you need certified explosion proof equipment. The AOX-Q-L Series provides Exdb II C T5 certification for use in petroleum refineries, chemical plants, and other areas where flammable gases or vapors could be present. This series also extends the thrust range from 2000N up to 40000N, covering heavier duty applications..
Avoiding Common Load Capacity Mistakes
There are a few common mistakes you’ll want to avoid for load capacity.
Underestimating Actual Loads
You need to factor in friction, acceleration forces, angle of operation, and any external forces acting on the system. All of these add to the total load the actuator sees.
Ignoring Side Loads
If your mounting geometry creates any lateral forces, add guide rails or redesign the mounting to eliminate them. Side loading is a fast track to failure.
Operating Too Close to Maximum Capacity
Running an actuator at 95% of its rated capacity doesn’t leave any room for variation or unexpected conditions. You’ll shorten its life dramatically.
Forgetting About Temperature
Operating in hot environments reduces load capacity because heat degrades lubricants and reduces motor performance. Industrial linear actuators typically handle ambient temperatures from negative 30°C to positive 70°C as standard, with some models rated down to negative 60°C for extreme cold.
Final Thoughts
Load capacity is more nuanced than just picking a force rating from a datasheet. You need to understand static versus dynamic loads, account for different load types, and factor in how the actuator’s design affects its capacity. Always include safety margins, respect duty cycle limits, and match the actuator’s capabilities to your application’s real world demands.
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