Gas Struts vs Gas Traction Springs: Key Differences

A compression gas strut pushes the piston rod outwards in its rest position, whereas a gas traction spring pulls it inwards.

When it comes to the controlled opening, closing, or holding of furniture fronts, gas-operated components are the standard in modern cabinetry. For joiners and fitters, selecting the exact mechanism is crucial for the function and durability of the build. Although both types appear very similar visually, they operate on opposite physical principles. The following technical comparison breaks down the differences, operating principles, and specific application areas in detail.

The Physical Basis: How Gas Springs Work

Both systems utilise a sealed cylinder tube filled with nitrogen under high pressure. A piston moves within this cylinder, displacing the gas. A small quantity of oil inside provides lubrication for the seals and simultaneously handles the end-position damping.

The decisive difference lies in the internal construction of the cylinder and the position of the piston, which reverses the direction of force. The mechanism can be compared to classic mechanical components: the compression variant behaves like a coil spring that responds to counter-pressure and seeks to expand, whilst the traction variant acts like a strong elastic band that remains contracted at rest.

What Is a Compression Gas Strut?

The compression gas strut is the standard fitting installed in most wall units and lift-up flaps.

In an unloaded state, the piston rod is fully extended. The compressed gas inside pushes permanently against the cross-sectional surface of the piston, driving it outwards. When you close a flap, you push the rod into the cylinder against the gas pressure, further compressing the gas. When you open the flap, the gas expands and pushes the rod back out. This process assists with lifting the weight.

Typical Features of a Compression Strut:

• Rest position: Extended.
• Force build-up: The highest force is required to compress the spring.
• Function: Lifts loads and holds them in the open position.

What Is a Gas Traction Spring?

The gas traction spring is a specialised fitting for constructions where a pulling force is required.

Here, the mechanics are reversed: in an unloaded state, the rod is fully retracted inside the cylinder. When you pull the rod out, you work against the gas pressure attempting to pull the piston back into its initial position. To achieve this, the annular surface of the piston (the side where the rod is attached) is pressurised in this design.

Typical Features of a Traction Spring:

• Rest position: Retracted.
• Force build-up: The highest force is required to pull the spring apart.
• Function: Decelerates falling loads or pulls components together.

The Differences in Direct Comparison

For construction planning, the technical parameters of both systems must be clearly distinguished. A mix-up leads directly to a malfunctioning furniture unit.

• Direction of Force:

  The compression strut generates an extension force, whilst the traction spring generates a tensile force. Both values are specified in Newtons (N).

• Installation Behaviour:

  A compression strut must generally be calculated in its compressed state (with the flap closed), as it pushes out upon opening. A traction spring is usually installed in an extended state and contracts when the unit is closed.

• End-Position Damping:

  With a compression strut, hydraulic damping (via the oil) acts in the extension direction to prevent the flap from hitting the top stop harshly. With a traction spring, damping acts in the pulling direction to gently decelerate movement as the rod slides back into the cylinder.

• Overall Length:

For an identical stroke (the maximum travel distance of the rod in mm), the traction spring is often slightly longer due to its design, as the internal gas chamber must be dimensioned differently.

Which Variant Should You Choose?

The choice between compression and traction depends entirely on the kinematics of the furniture front.

Application Scenarios for Compression Gas Struts

Choose this fitting when a flap opens upwards and must be held against gravity.

• Kitchen wall units: The lift-up flap is pushed upwards by the strut and held open.
• Chests and toy boxes: The lid is supported during opening and does not drop shut uncontrolled.
• Ottoman bed frames: Heavy slatted frames are lifted effortlessly via the compression mechanism.

Application Scenarios for Gas Traction Springs

This fitting is used when a flap opens downwards and gravity needs to be braked, or when components must be actively drawn together.

• Bar cabinets and bureaux: The downward-opening flap is supported by the traction spring. The spring pulls inwards, preventing the heavy wooden panel from crashing down.
• Shoe storage units: On large drop-front compartments, the traction mechanism decelerates the opening movement.
• Concealed floor hatches: When a heavy hatch in the floor needs to be lowered gently.

Dimensioning: Calculating Force and Stroke

Regardless of the design type, two core values must be calculated before installing the fitting.

1. Nominal Force (N):

   The force of the spring must match the weight of the front precisely. As a rule of thumb, 10 N corresponds to a lifting capacity of approximately 1 kg. A strut rated at 250 N can therefore move around 25 kg. However, with a furniture flap, the lever arm and centre of gravity play a role. If the spring is too strong (e.g. 450 N for a lightweight MDF board), the flap can barely be closed. If it is too weak, the flap will not stay open.

2. Stroke:

The stroke in mm defines the opening angle. A typical stroke for kitchen wall units is between 90 mm and 120 mm. The total length of the strut consists of the cylinder length plus stroke plus fixing eyelets.

FAQ: Frequently Asked Questions on Fitting and Selection

Can I replace a compression gas strut with a gas traction spring? No. The components operate in opposite force directions. If you fit a compression strut to a downward-opening bar cabinet, the strut will force the flap downwards with full power instead of braking it.

How is the spring installed correctly? The installation orientation is crucial for service life and damping. A compression gas strut should be mounted so that the piston rod points downwards when the flap is closed. This ensures the oil remains at the seal, lubricating it and providing smooth braking during opening.

What fixing options are available? In furniture hardware, systems with a ball joint or a simple screw-on eyelet are most commonly used. A ball joint (usually with a 10 mm diameter) offers the advantage of compensating for slight lateral tolerances during installation on chipboard, preventing cylinder binding.

Why does my spring lose force after several years? The seals inside the cylinder are subject to natural wear. Through microscopic gaps, nitrogen gradually escapes over the years. When the flap no longer stays up, the fitting must be replaced. Refilling is not possible with furniture fittings. When replacing, check the printed N rating (e.g. 320 N) and the length in mm.