The Great Gas Strut Debate: Gas Springs, Boot Shocks, and Gas Lifts Explained
If you have ever tried replacing the struts on your car's boot, the canopy of your bakkie, or the cylinder under your office chair, you've likely run into a wall of confusing terminology. Here in South Africa, mechanics, office suppliers, and DIY enthusiasts often use "gas lift," "boot shock," and "gas spring" interchangeably.
Are they the same thing? Fundamentally, yes. Practically, no.
Let's lift the bonnet on this terminology and break down exactly what sets them apart, so you never buy the wrong part again.
1. Gas Springs: The Parent Term
Before we dive into the specific types, you need to know the umbrella term: Gas Spring (often called a gas strut).
A gas spring is a hydro-pneumatic energy storage device. Inside a sealed steel cylinder, you have a sliding piston rod, pressurised nitrogen gas, and a small amount of lubricating oil.
- The Gas: Acts exactly like a mechanical coil spring. The higher the nitrogen pressure, the harder the rod pushes outward.
- The Oil: Provides damping and lubrication. It ensures the movement is smooth and controlled, preventing the rod from violently snapping open and causing damage.
Every boot shock and gas lift is a type of gas spring, but they are engineered with distinctly different internal valves for entirely different jobs.
2. Boot Shocks (Non-Locking Gas Springs)
Also known as: Tailgate struts, bonnet struts, canopy gas struts.
These are standard, non-locking gas springs. Their sole purpose in life is to constantly push outward.
How they work:
When you unlatch your car's boot, the boot shock assists you by pushing the heavy metal lid upward and holding it firmly against gravity. Because they don't have a locking valve, you can compress them simply by applying physical force (like pulling the boot shut).
The defining feature: End-of-Stroke Damping
If a boot shock only had gas inside, your boot would fly open and smash the hinges. To prevent this, manufacturers design them so that as the rod reaches full extension, the piston passes through the internal oil. This creates hydraulic resistance, gently slowing the boot down just before it reaches the top.
3. Gas Lifts (Locking Gas Springs)
Also known as: Office chair cylinders, height-adjustable struts.
Unlike a boot shock, a gas lift is a locking gas spring. If you take an office chair cylinder out of the box and try to compress it with your hands, it won't budge. It behaves like a solid rod until you activate it.
How they work:
Gas lifts have a built-in release valve, usually controlled by a small push-pin at the very top of the cylinder. When you pull the lever on your office chair, the lever presses this pin.
Opening the valve allows the pressurised gas to flow through the piston, letting the seat rise (or sink under your weight). The brilliant bit? The moment you let go of the lever, the valve snaps shut, locking the piston rigidly in place so your chair doesn't bounce around whilst you work.
At a Glance: The Quick Comparison
| Feature | Boot Shock (Cars/Canopies) | Gas Lift (Chairs/Stools) |
|---|---|---|
| Primary Job | Lift heavy objects & hold them open | Variable height adjustment |
| Valve Type | None (always pushing) | Push-pin release valve |
| Movement Behaviour | Continuous outward travel | Locks rigidly until manually triggered |
| Damping Profile | Heavy slowing at the end of extension | Smooth, continuous travel when unlocked |
The Bottom Line: If it holds a lid open on its own, it’s a boot shock. If it needs a lever to move and locks into place, it’s a gas lift. Both are brilliant pieces of engineering—just don’t try putting a chair cylinder on your bakkie canopy!