Gas Struts Explained: Force, Measurement and Applications
Gas struts are hydro-pneumatic devices that use compressed nitrogen gas and oil to provide controlled extension force for lids, hatches and panels. They consist of a pressure cylinder, piston rod and sealed end fittings, delivering consistent force throughout their stroke for hold-open applications.
⚡ In a Rush? Key Takeaways
- Gas struts>Force rating in Newtons determines lift capacity – calculate using (weight × distance to CG) ÷ (mounting distance × quantity)
- Stroke length must match lid travel – measure eye-to-eye when fully extended minus compressed length
- End fittings affect installation – ball socket for quick release, clevis for high vibration environments
- Temperature extremes reduce force – specify low-temperature rated struts below 0°C for outdoor applications
- ✅ Always verify force requirements with our Gas Spring Force Calculator before purchasing
How do I calculate the required force for a gas strut application?
Required force equals (lid weight multiplied by distance from hinge to centre of gravity) divided by (number of struts multiplied by distance from hinge to strut mounting point).
Force calculation starts with determining the lid’s weight and centre of gravity position. For a horizontally hinged lid, measure the distance from the hinge axis to the lid’s centre of gravity (CG). Multiply the lid weight (in Newtons) by this distance to get the torque requirement.
Next, determine the mounting geometry. Measure the distance from the hinge axis to where the gas strut will attach on the lid. Divide the torque requirement by this distance multiplied by the number of struts being used. This gives the minimum force per strut in Newtons.
Always add a 15-20% margin to account for friction, temperature variations and long-term force loss. For example, a 100N lid requiring 50N of assist should use a 60-70N strut. Our Gas Spring Force Calculator automates this calculation using lid weight, hinge distance, stroke length and mounting angle inputs.
- Measure lid weight accurately using scales – estimate leads to undersizing
- Locate centre of gravity by balancing lid on a narrow edge
- Use metric units consistently – convert imperial measurements to Newtons and millimetres
- Verify calculation with physical test using temporary weights before final selection
What is the correct way to measure a gas strut for replacement?
Measure eye-to-eye length when fully extended, then fully compressed – stroke is the difference between these two measurements.
To measure an existing gas strut, first fully extend it by holding the lid open. Measure from the centre of one eyelet to the centre of the opposite eyelet – this is the extended length. Then fully compress the strut (lid closed) and take the same eye-to-eye measurement – this is the compressed length.
The stroke length is calculated by subtracting the compressed length from the extended length. For example, if extended length is 300mm and compressed length is 180mm, the stroke is 120mm. This measurement must match your application’s travel requirement.
Additionally, note the force rating usually printed on the strut body (e.g., 200N). When replacing, match both the stroke length and force rating within 10-15% for equivalent performance. Always replace struts in pairs even if only one appears failed.
- Fully extend the lid and secure it safely
- Measure eye-to-eye length with callipers or tape measure
- Fully compress the lid and repeat measurement
- Record extended length, compressed length and calculate stroke
- Check force rating printed on the strut cylinder body
Where are gas struts commonly used across different industries?
Gas struts appear in automotive bootlids, furniture cabinet doors, industrial machine guards and marine hatch covers – each application requires specific corrosion and temperature considerations.
In automotive applications, boot and bonnet struts typically range from 150-400N depending on vehicle size. European models often use 200-300N for bootlids while larger SUVs may require 400N+ units. Marine applications demand 316 stainless steel construction to resist saltwater corrosion, with force ratings adjusted for hatch angle at heel.
Furniture applications like overhead cabinet doors usually require 60-100N struts, with higher forces needed for tall or heavy doors. Industrial machinery guards often use damped struts to prevent sudden closure, with force calculated based on guard weight and pivot point distance.
Caravan storage lockers benefit from cycle-rated struts (50,000+ cycles) due to frequent daily use. Temperature extremes in caravan applications necessitate low-temperature gas charges to maintain force output in winter conditions down to -30°C.
| Application | Typical Force Range | Special Considerations |
|---|---|---|
| Automotive Bootlid | 150-400N | UV-resistant seals, corrosion-resistant fittings |
| Overhead Cabinet | 60-100N | Damped extension, soft-close options |
| Marine Hatch | 100-300N | 316 stainless steel, full submersion rated |
| Industrial Guard | 50-200N | Dust seals, high-cycle ratings, adjustable force |
What factors affect gas strut performance and lifespan?
Temperature, corrosion, cycling frequency and incorrect force specification are the primary factors affecting gas strut performance and operational lifespan.
Temperature significantly impacts force output – gas struts lose approximately 1.5% of their rated force per degree Celsius below the standard 20°C rating. At -20°C, a standard strut may deliver only 70% of its rated force, necessitating low-temperature rated units for cold environments.
Corrosion attacks the piston rod and seals, particularly in marine or road-salt environments. Chrome plating thickness directly correlates with corrosion resistance – 10mm minimum rod diameter provides significantly better protection than 8mm budget options. 316 stainless steel rods and bodies are essential for permanent marine immersion.
Cycling frequency affects seal wear – standard struts rated for 50,000 cycles may fail prematurely in high-use applications like caravan lockers opened 20 times daily. Specify cycle-rated units (100,000+ cycles) for doors opened more than 5 times per day. Incorrect force specification causes either insufficient hold-open force or excessive closing resistance, both leading to premature failure through over-extension or rod bending.
- Check operating temperature range matches application environment
- Inspect piston rod for pitting or corrosion every 12 months in harsh environments
- Lubricate end fittings annually with silicone-based lubricant – never use petroleum jelly
- Replace struts in pairs to maintain balanced force and prevent uneven wear
- Monitor closing speed – sudden increase indicates seal wear and requires replacement
