Traction Gas Struts

Traction Gas Springs for Controlled Pulling and Return Movements

Traction gas springs generate a pulling force and therefore operate in the opposite direction to conventional compression gas springs. In the unloaded condition, the piston rod is retracted into the cylinder. When the piston rod is pulled out, the traction gas spring attempts to retract it again.

This allows movable components to be pulled back, closed in a controlled manner or continuously tensioned in a defined direction. Traction gas springs are particularly suitable for designs where a conventional compression gas spring cannot be used because of the direction of movement or the available installation space.

Typical applications include downward-opening flaps, ramps, trapdoors, retractable stairs, machine covers and mechanical tensioning systems.

Use the product table above to select a suitable traction gas spring by piston rod diameter, cylinder diameter, retracted length, stroke, pulling force and connection thread.

Meaning of the Specifications in the Product Table

For the versions offered, the fully extended length is calculated from the retracted length L and the maximum stroke St:

L1 = L + St

The actual distance between the mounting points may also be increased by the end fittings used.

Difference Between a Traction Gas Spring and a Compression Gas Spring

A conventional compression gas spring extends in the unloaded condition and generates a pushing force. It is commonly used to lift flaps or hold them in the open position.

A traction gas spring operates in the opposite way. Its piston rod is retracted in the unloaded condition. When the piston rod is pulled out, the spring generates a force in the retracting direction.

Traction gas springs are therefore particularly suitable where:

• a component must be actively pulled back,

• a downward-opening flap must be closed in a controlled manner,

• the gas spring must be positioned above or inside the structure,

• continuous tensile preload is required,

• there is no suitable installation space for a compression gas spring.

Traction gas springs are not simply dampers. They generate an active return force. Where only the movement speed needs to be reduced, a hydraulic damper may be more suitable.

How to Select the Right Traction Gas Spring

Proceed in the following order:

1. Determine the installation lengths: Measure the distance between the mounting points in the fully retracted and fully extended positions.

2. Define the required stroke: The required movement must remain within the maximum stroke St. Allow sufficient stroke reserve.

3. Determine the pulling force: Consider the weight, centre of gravity, lever arm, mounting points and installation angle of the application.

4. Check the overall size: Verify the piston rod diameter R, cylinder diameter T and possible interference throughout the complete movement.

5. Select the connection thread: Thread M must be compatible with the intended end fittings.

6. Consider the operating environment: Check humidity, corrosion, temperature, dust and possible contact with cleaning agents or other media.

7. Test the movement: Make sure that the traction gas spring is loaded only in its intended pulling direction.

The required pulling force cannot be determined from the weight of the component alone. The position of the centre of gravity and the mounting points have a major influence on the effective lever arm.

Pulling Force and Force Characteristics

F1 is the nominal pulling force of the traction gas spring. As the piston rod is pulled out, the gas pressure inside changes, which may cause the pulling force to increase over the stroke.

Friction also occurs at the seals and guides. The forces during extension, standstill and retraction may therefore differ slightly.

Temperature also influences the spring force. At higher temperatures, the gas pressure increases; at lower temperatures, it decreases. The traction gas spring should therefore be selected for the actual operating conditions.

On suitably equipped versions, the pulling force can be reduced using a release valve. Pressure should only be released gradually and in accordance with the technical instructions. The force cannot subsequently be increased by the user.

Installation and Safety Recommendations

Traction gas springs are sealed components under high internal pressure. They must not be opened, drilled, heated, welded or mechanically modified.

For reliable operation, we recommend:

• installing the traction gas spring in the fully retracted condition,

• applying the load only in the axial direction,

• avoiding lateral forces, misalignment and tilting,

• using suitable ball joints or other articulated end fittings,

• allowing sufficient clearance at the mounting points,

• protecting the piston rod against scratches, dirt, paint and damage,

• providing adequate stroke reserve and separate mechanical end stops.

The traction gas spring must not be used as a mechanical end stop. The structure itself must limit the end position in the pulling direction.

During installation, the movable component must be supported separately. The traction gas spring must only be installed or removed when the flap, ramp or cover is secured against unintended movement.

Where two traction gas springs are used in parallel, they should have the same pulling force and be installed symmetrically. Different forces may result in uneven loading and jamming of the structure.

Suitable ball joints, eye ends and clevis ends can be found in our gas spring end fittings range. Ball studs and mounting brackets are available in the gas spring mounting brackets section.

Surface Finish and Operating Conditions

The T-series traction gas springs have a black pressure tube and a treated or nitrided piston rod. Nitriding creates a hard, low-friction surface and improves corrosion resistance.

However, this version is not equivalent to a fully stainless steel traction gas spring. Suitability must be assessed separately for permanently humid environments, salt water, chlorides or aggressive cleaning agents.

The piston rod must not be additionally greased, oiled or painted. Adhering dirt and damaged surfaces may impair the sealing system and cause premature loss of force.

Typical Applications

Traction gas springs are commonly used for:

• wheelchair and vehicle ramps,

• downward-opening rear and side flaps,

• trapdoors and floor hatches,

• retractable stairs and loft ladders,

• machine covers and protective panels,

• conveyor systems and tensioning devices,

• movable furniture and flap elements,

• applications requiring continuous tensile preload.

They are particularly suitable where a movement must be returned in a controlled manner or a component must be pulled reliably in the retracting direction.

Frequently Asked Questions About Traction Gas Springs

What is the main difference from a compression gas spring?

A compression gas spring attempts to extend. A traction gas spring, by contrast, attempts to pull its extended piston rod back into the cylinder.

What does length L mean?

L is the length of the traction gas spring in the retracted condition according to the product drawing. The extended length is calculated by adding the stroke St to L.

Can a traction gas spring be used as a cable or tension rod?

No. It must be guided and loaded axially. Lateral forces or tilting may damage the seals, guides and piston rod.

Can the pulling force be adjusted afterwards?

On versions with a release valve, the pulling force can be reduced gradually. Whether the selected article has such a valve must be checked in the product specifications.

Can a traction gas spring be used as an end stop?

No. The application requires separate mechanical end stops and sufficient reserve before the maximum stroke is reached.