Tension Springs vs Gas Springs: When to Use Each and How to Specify

The core distinction between tension springs and gas springs lies in their force delivery mechanism: tension springs exert increasing force with extension, whereas gas springs provide near-constant extension force that varies with stroke position and temperature. This fundamental difference dictates their suitability for specific mechanical applications where controlled motion and hold-open performance are critical.

How do tension springs work and where are they commonly used?

Tension springs store energy when extended, delivering force proportional to deflection per Hooke’s Law, making them ideal for return mechanisms and vibration damping where increasing resistance is beneficial.

Tension springs (also called extension springs) consist of coiled wire with initial tension, requiring a minimum load to begin extension. Force increases linearly with extension distance, characterized by the spring rate (N/mm). Common applications include carburetor throttles, trampoline mounts and garage door counterbalance systems where the spring returns components to a neutral position.

In industrial settings, tension springs appear in clutch mechanisms, valve return systems and electrical switchgear. Their predictable force curve suits applications needing progressive resistance, but they cannot provide constant force throughout travel — a critical limitation for lid lift scenarios where consistent hold-open force prevents drift under varying loads.

• Typical spring rates: 5-50 N/mm for light duty, 50-500 N/mm for heavy industrial
• Maximum extension: usually 25% of free length to avoid permanent set
• Material: music wire (ASTM A228) for general use, stainless steel (AISI 302) for corrosive environments
• End types: machine hooks, crossover center hooks, extended hooks or threaded inserts

How do gas springs work and where are they commonly used?

Gas springs use compressed nitrogen to deliver near-constant extension force throughout stroke, with force variation primarily affected by temperature and piston seal friction, making them suitable for controlled lift and hold-open applications.

Gas springs (gas struts, gas lifts) contain nitrogen gas pressurized to 80-160 bar and a small volume of hydraulic oil. The oil provides damping during extension while the nitrogen generates force via piston area pressure. Force remains relatively flat across stroke (±10-20%) unlike mechanical springs, with mid-stroke force being the standard rating specification.

Automotive applications dominate usage: boot/bonnet struts, tailgate lifts and sunroof mechanisms. Industrial applications include medical equipment enclosures, server rack doors and machine guard Interlocks. Furniture applications cover cabinet lifts, ottoman beds and TV lift mechanisms where consistent hold-open force enhances usability and safety.

1. Force range: 10N to 2,500N+ for stock units; custom up to 10,000N
2. Stroke length: 20mm to 600mm+ in 10mm increments
3. Temperature compensation: standard units lose ~0.6% force per °C below 20°C rating
4. End fittings: ball socket (8mm/10mm), clevis, eyelet and stud mounts for diverse attachment

What are the key functional differences between tension springs and gas springs?

Tension springs provide increasing resistive force with extension while gas springs deliver near-constant assistive force throughout stroke, creating opposing force curves that dictate application suitability.

The force curve represents the most significant difference: tension springs follow a linear positive slope (force ∝ extension) whereas gas springs exhibit a near-horizontal curve with slight decline at full extension due to gas compression. This makes tension springs unsuitable for lift-assist roles where decreasing effort is desired near full open, while gas springs prevent sudden closure by maintaining resistive force against lid weight.

Installation geometry further differentiates them: tension springs require axial alignment for effective force transfer, whereas gas springs accommodate angular misalignment through ball socket end fittings. Cycle life also varies significantly — standard tension springs endure 50,000-100,000 cycles while industrial gas springs rate for 100,000-200,000 cycles due to lower internal friction and sealed design.

Parameter	Tension Spring	Gas Spring
Force Curve	Linear increase with extension	Near-constant (±15%) across stroke
Force Direction	Resistive (opposes extension)	Assistive (aids extension)
Temperature Sensitivity	Low (<0.1%/°C)	Moderate (0.5-0.7%/°C)
Damping	None inherent	Hydraulic oil provides extension damping
Typical Cycle Life	50,000-100,000	100,000-200,000 (industrial grade)

How do I specify a gas spring for lid lift or hatch applications?

Specify gas spring force using the formula: (Lid weight × Distance from hinge to CG) ÷ (Number of springs × Distance from hinge to spring mount), then select next standard size up for margin.

Begin by measuring lid weight and locating its centre of gravity relative to the hinge axis. Calculate required force per spring using the leverage equation, then add 15-20% margin to accommodate temperature extremes and long-term force loss. Stroke length must match the vertical travel of the lid converted to spring mounting point distance — determined through CAD modelling or physical measurement of compressed and extended positions.

End fitting selection depends on mounting geometry: ball sockets simplify installation but limit angular tolerance (<5°), while clevis brackets handle higher misalignment (<10°) and vibration environments. Always verify compressed length fits within the available space when the lid is closed, allowing 3