Gas Springs Guide: How to Select the Right Strut for Your Application
Gas springs are not interchangeable components. Selecting the wrong force rating, stroke length, or end fitting leads to premature failure, safety hazards, or operational inefficiency. This guide details the engineering parameters used by industrial specifiers across automotive, furniture, and machinery applications in 2026. As an engineer with 18 years in the field, I consistently observe that the most common point of failure is not a manufacturing defect, but a fundamental misunderstanding of the force-to-geometry relationship.
⚡ In a Rush? Key Takeaways
- Standard gas springs lose 15-20% of force at -10°C, requiring uprate for cold environments
- The correct stroke length must be measured as eye-to-eye distance change, not lid angle
- Caravan and marine applications demand 50,000+ cycle-rated struts to avoid early failure
- Industrial gas springs require 316 stainless end fittings in corrosive environments to survive 8+ years
- ✅ Always use the Gas Spring Force Calculator before selecting any replacement strut
How do I determine the correct force rating for a gas spring?
Gas spring force is calculated by multiplying the lid weight by the distance from hinge to center of gravity, then dividing by the product of spring count and mounting distance from hinge.
Selecting a force rating requires more than just knowing the weight of your panel. You must account for the moment arm—the distance from your pivot point (the hinge) to the center of gravity (CG) of the object being lifted. If you rely on a rough estimate, you will either have a lid that won’t stay open or one that requires significant effort to close, potentially damaging the hinge or the mounting bracket.
One thing I see constantly is buyers ordering by part number alone without checking the extended length. The gap between compressed and extended determines whether your boot stays open hands-free or drops on your head. I always tell people: measure your existing strut fully extended, not just the body length printed on the packaging.
What is the formula for calculating gas spring force?
The force required per gas spring equals (lid weight × distance from hinge to center of gravity) divided by (number of springs × distance from hinge to spring mounting point).
Engineers commonly miscalculate force by assuming the full weight of the lid must be supported directly by the spring. This ignores basic lever mechanics. The force is distributed across the pivot axis and the spring mounting point. For example, a 50N lid with center of gravity 300mm from the hinge, mounted with two springs at 150mm from the hinge, requires a specific calculation to ensure the mechanical advantage is sufficient to keep the system in equilibrium.
When performing this calculation, it is vital to account for the “over-center” position. If your gas spring is perfectly vertical at the open position, you may have issues with closing tension. Ideally, the spring should remain at a slight angle to ensure the force profile transitions smoothly during the closing arc. If you are unsure about these inputs, our Gas Spring Force Calculator handles the geometry conversion automatically to prevent common errors.
What factors influence force loss over time?
Force loss occurs due to nitrogen gas permeation through internal seals, accelerated by extreme temperature cycling and mechanical vibration.
Nitrogen gas, which provides the internal pressure, will naturally permeate through rubber seals at a microscopic level over many years. However, in my 18 years of specifying components, I have found that accelerated failure is almost always linked to environment. In the UK and European markets, temperature extremes are the primary culprit. A strut that works perfectly in a 20°C workshop can effectively lose 20% of its working force when the ambient temperature drops below freezing.
Furthermore, high-cycle applications—such as those found in industrial packaging machinery or frequently accessed storage compartments—increase seal friction. If your application exceeds 10,000 cycles per year, standard grade gas springs will likely fail prematurely. In these scenarios, I specify industrial-grade units with reinforced seals and higher-density oil damping to maintain the force rating throughout the design life of the equipment.
| Factor | Impact on Force | Mitigation Strategy |
|---|---|---|
| Cold Temperature (-10°C) | -15% to -20% | Increase Newton rating by 20% |
| Vibration/Road Travel | Seal degradation | Use shock-resistant end fittings |
| Corrosion (Marine/Coastal) | Surface pitting on rod | Specify 316 Stainless Steel rods |
| High-Cycle Usage | Internal seal wear | Use industrial-grade, cycle-tested struts |
How do I correctly measure stroke length and mounting points?
Stroke length is the distance between the center of the mounting eyelets when fully extended minus the compressed length, plus required preload.
Most industrial specifiers make the mistake of measuring the cylinder body length and assuming that defines the stroke. This is incorrect. The stroke is defined by the physical travel of the internal piston rod. If you do not allow for the correct stroke, the gas spring will ‘bottom out’ before the lid is fully open, creating a massive stress concentration at the mounting point that can tear metal brackets away from the frame.
I always suggest sketching the arc of motion in a CAD environment. You need to identify the exact distance between your two mounting points at the closed position and the fully open position. The difference between these two measurements is your minimum required stroke. Always add an extra 10-15mm of buffer so the spring acts as a cushion rather than a physical stop for the door or hatch.
What is the importance of the rod-end orientation?
Most gas springs must be mounted rod-end down to ensure the internal seal stays lubricated by the oil reservoir, preventing premature leaks.
One of the most frequent technical support queries I handle involves premature seal failure. When I visit a site to investigate, I often find the spring mounted with the rod end pointing upward. This causes the internal hydraulic oil to settle at the base of the cylinder, leaving the primary rod seal dry. Without constant lubrication, the rubber seal hardens and cracks, leading to rapid gas loss within months rather than years.
If your specific application requires the rod to be pointed upward due to space constraints, you must specify a gas spring that includes a specially designed internal oil chamber or a “universal orientation” seal. These units cost slightly more, but they are the only way to avoid the catastrophic seal failures I see in incorrectly installed machinery. For standard industrial equipment, stick to the rod-down orientation whenever possible; it is a simple rule that adds years to the component’s lifespan.
Can I use stainless steel struts in all environments?
Stainless steel is mandatory for marine and chemical environments, but standard carbon steel is more cost-effective for general indoor industrial use.
There is a common misconception that stainless steel is always the superior choice. From an industrial engineering perspective, this is not true. In a dry, temperature-controlled warehouse or office environment, carbon steel with a high-quality zinc coating is more than sufficient and provides excellent value. Using 316 stainless steel in these scenarios is an unnecessary expense, as there is no functional performance benefit in a non-corrosive environment.
However, once you move into the marine or agricultural sector, the game changes. Salt spray, road salt in the UK, and chemical fertilisers are incredibly aggressive against the chrome-plated rods of standard struts. If you are fitting a hatch on a canal boat or a storage locker on a farm vehicle, 316-grade stainless steel is non-negotiable. If you don’t specify it, you will be replacing the struts every winter, which eventually costs more than the initial upgrade to stainless.
What are the safety requirements for end-fitting selection?
End fittings must be rated for the peak dynamic load of the system to prevent shearing or disengagement during operation.
While the gas spring provides the force, the end fittings (eyelets, ball joints, or clevises) transmit that energy to the structure. Always ensure the fitting’s material—typically nylon or steel—is rated to withstand the force output of your spring. In high-vibration applications, I strongly recommend using metal-to-metal ball joints secured with safety clips to prevent the joint from popping off during travel, which poses a significant injury risk to operators.
- General Indoor/Office: Zinc-plated carbon steel (Budget-friendly)
- Food/Pharmaceutical: 316 Stainless (Hygiene and wash-down compatibility)
- Marine/Coastal: 316 Stainless with sealed end fittings (Corrosion protection)
- Heavy Agriculture: Powder-coated carbon steel or Stainless (Resistant to harsh chemicals)
For bespoke or bulk orders, or if you need assistance determining the exact force requirement for your specific project, feel free to contact our industrial technical team. We can provide custom calculations to ensure your application meets safety and performance standards for its full service life. Don’t leave your assembly to chance—measure twice and verify your force curve with our expert team.
