Lift Supports Guide: Selection, Applications and Replacement
Lift supports, also known as gas springs or gas struts, are hydraulic devices that use compressed nitrogen to provide controlled lift and hold for lids, hatches, and panels. This guide covers their working principle, selection criteria, applications, and replacement procedures to help engineers and buyers specify the correct component for their specific application.
⚡ In a Rush? Key Takeaways
- Lift support force is calculated as (lid weight × distance from hinge to CG) ÷ (number of supports × distance from hinge to mounting point)
- Standard lift supports lose approximately 1.5% force per °C below rated temperature, requiring 20% uplift for cold environments
- Automotive boot struts typically require 200-400N force with 200-350mm stroke, measured eye-to-eye when fully extended
- ✅ Always verify force rating in Newtons and stroke length in millimetres before purchasing — never guess specifications
What are lift supports and how do they work?
Lift supports contain nitrogen gas and hydraulic oil in a sealed cylinder, producing extension force that varies with stroke position and temperature.
The core component is a pressure tube filled with nitrogen gas at high pressure (typically 1000-3000 psi) and a small amount of hydraulic oil. A piston rod with sealing system moves inside the tube. When compressed, the gas pressure increases, creating a force that extends the rod. The oil provides damping to control extension speed.
Force output follows the ideal gas law: force increases as the rod compresses (volume decreases). The force rating printed on the body is measured at mid-stroke under standard conditions (20°C/68°F). Force changes approximately 1.5% per °C deviation from this temperature.
What is the basic principle behind a gas lift support?
Compressed nitrogen exerts force on a piston, with oil providing damping — force increases as the rod compresses due to reduced gas volume.
Unlike mechanical springs, gas springs provide near-constant force through most of the stroke due to the compressibility of nitrogen. The force curve is relatively flat compared to mechanical springs, making them ideal for applications requiring consistent lift effort. The hydraulic oil prevents sudden extension and provides end-of-stroke cushioning.
What are the main components of a lift support?
Main components: pressure tube, piston rod, piston with seals, nitrogen charge, hydraulic oil, and end fittings (eyelet, ball socket or clevis).
The pressure tube (usually steel) contains the nitrogen and oil. The piston rod (chrome-plated steel) extends/retracts. Seals prevent gas leakage and oil contamination. End fittings attach to the application — common types include 10mm ball sockets for easy installation, clevis brackets for high-vibration environments, and eyelets for bolted mounts. Rod diameter typically ranges from 6mm to 14mm depending on force rating.
How do I select the correct lift support for my application?
Selection requires calculating required force, measuring stroke length, and considering mounting angle, temperature and end fitting type.
Begin by calculating the force needed to lift and hold your lid or hatch. Measure the lid weight, centre of gravity distance from hinge, and mounting geometry. Force requirements change with temperature — applications below 0°C require 20-30% force uplift. Stroke length must match the lid’s travel path, accounting for mounting point movement. Always verify specifications in Newtons and millimetres.
What force rating do I need for my lid or hatch?
Required force = (lid weight × distance from hinge to centre of gravity) ÷ (number of supports × distance from hinge to mounting point), with 15% safety margin.
For a horizontally opening lid: measure lid weight in kg or lbs, find centre of gravity (usually halfway for uniform lids), measure distance from hinge to centre of gravity (L1), and distance from hinge to lift support mounting point (L2). Formula: F = (Weight × L1) ÷ (Number of supports × L2). Example: 10kg lid, L1=200mm, L2=150mm, 2 supports → F = (10 × 9.81N × 200) ÷ (2 × 150) = 65.4N per support. Select next standard size up (70N or 80N).
How do I measure the required stroke length?
Stroke = maximum distance between mounting points (lid open) minus minimum distance (lid closed), measured in millimetres with 10% preload added.
Do not guess stroke from lid angle — model the mounting points in both open and closed positions. Measure eye-to-eye or stud-to-stud distance when lid is fully closed (minimum) and fully open (maximum). The difference is the required stroke. Add 10-15% for compression preload to ensure full extension. For example: closed position 200mm, open position 350mm → stroke = 150mm + 15% = 173mm → select 180mm stroke standard.
What mounting angle and end fittings should I consider?
Mounting angle affects force direction — ideally align within 15° of lid’s force vector; use ball sockets for <15° misalignment, clevis for higher angles or vibration.\
How do I install or replace lift supports?
Follow proper safety steps, align mounts, and use correct tools to avoid rod damage or seal failure.
Before removal, support the lid or hatch securely to prevent sudden drop. Loosen the end fittings (usually ball sockets, clevis pins, or bolts) and note their orientation. When installing the new lift support, compress the rod slightly to match the preload, then attach the fittings ensuring they move freely without binding. Tighten to the manufacturer’s torque specification, typically 5‑10 Nm for ball sockets and 8‑15 Nm for clevis bolts. Finally, operate the lid through its full range to verify smooth motion and correct holding force.
