Gas struts FAQ´s

  • 1. Why is there a warning on the gas strut?

    Gas struts are filled with compressed nitrogen. The warning is intended to prevent unauthorized people from opening the gas strut or making other changes to the gas strut, which negatively impact the strength of the pressure tube.

  • 2. Can gas struts explode?

    No. The pressure tubes of all SUSPA pressure tubes have wall thicknesses and materials that are dimensioned so that there is a sufficient level of safety against bursting in all conceivable functional states.

  • 3. What are SUSPA gas struts filled with?

    Only nitrogen is used as the pressure medium in SUSPA gas struts. About 75% of the air we breath consists of this gas. Nitrogen is absolutely safe and harmless to health. In addition, nitrogen does not burn. On the contrary, nitrogen is used in the chemical industry to prevent and extinguish fires. In addition, every SUSPA gas struts contains flame-retardant oil to lubricate the seals and to achieve certain functions, such as damping or rigid locking.

  • 4. How high is the pressure in a gas strut?

    The filling pressure of SUSPA gas struts depends on the extension force and the geometry and is between 10 and 230 bar.

  • 5. How does a gas strut work?

    Inside a gas strut, the filling pressure acts on both surfaces of the piston. Once this is firmly bonded with the piston rod, the piston surface on the piston rod side is reduced by the cross-section of the piston rod. This results in a differential pressure on the piston, which acts in the extension direction. The size of the force [F] is equal to the product from the filling pressure [p] and the piston rod cross-section surface [A]. The following formula applies: F = p x A

  • 6. What is "F1 force?"

    The "F1 force" is the designed force of SUSPA gas struts. This is measured when the piston rod of the gas strut is extended to 5 mm. It should be noted that the measured point of a significantly shorter position is approached with a defined speed and the value of the "F1 force" is read only about 3 seconds after the measurement devices comes to a standstill. The measurement must take place at 20°C gas strut and room temperature.

  • 7. Does the force of the gas strut change when displacing the piston rod?

    Yes. The inner volume of the gas strut is closed to the outside. This means that the filled gas volume can only occupy the free space in the pressure tube that is not needed for components or oil. By pushing the piston rod in, this free space [V] is reduced by the inserted piston rod volume. Because the same gas volume has a smaller volume available, the pressure [p] in the gas strut increases. This formula applies: p2 = (V1 / V2) x p1 The index [1] corresponds to the piston rod position before moving displacement and index [2] after displacement. The force [F] can also be used for the pressure [p] in this formula due to the correlation of the gas strut force with the filling pressure.

  • 8. Does the force of a gas strut differ between retraction and extension?

    Yes. A friction force [FR] is created by the seal contacting the piston rod and the piston contacting the inside of the pressure tube. This frictional force counteracts the movement direction of the piston rod. This means: During extension, the gas strut force [F = A x p] is reduced by the friction and a force increased by the amount of friction must be applied to push the piston rod in. This results in the following formula correlations: FOut = (A x p) - FOut; FIn = (A x p) + FIn  Since the gas strut friction [FRGF] equals the difference of the insertion and extension force, the following applies: FRGF = FIn + FOut

  • 9. Is it possible to manufacture a gas strut without friction?

    No. So that the gas filling does not escape from the pressure tube, a hermetic seal of the gas strut interior must be created, even at the moving piston rods. To achieve a hermetic seal, the piston rods and the seal must be in contact with a sufficient surface pressure. The result of the contact of two bodies is always a frictional force. The sealing of SUSPA gas strut is designed so that the piston rods slide on the seal when displaced. The resulting friction is reduced to a minimum in SUSPA gas struts due to a careful selection of the materials and lubricants used.

  • 10. What does the expression "damping" mean with a gas strut?

    Due to the gas strut structure, the interior of the gas strut is divided into two sub-spaces (chambers) by the piston, which is permanently connected with the piston rod. When the piston rod is displaced, the gas flows into a special connection channel through the piston from one chamber to the other. The structural design of this connection chamber has an effect on how big the resistance is that has to be overcome in order to press the gas through the piston. If the resistance is high, this is called a high "damping." The "damping" only occurs when the piston rod is moving and is used in gas struts above all to reduce the extension or insertion speed. In application, a gas strut with a higher damping with all other installation conditions that are the same will insert and extend more slowly than a gas strut with a lower damping.

  • 11. Can the damping of gas struts be changed?

    The damping of SUSPA gas struts can be preset by using different "damping discs." Furthermore, special "dampings" (e.g. end position damping or insertion damping) can be achieved by filling with larger oil quantities. Here, a larger resistance must be overcome to press the oil through the piston than if gas is flowing through the piston.

  • 12. What is the difference between a gas strut and a damper?

    In general, a gas strut is an energy storage device and a damper is an energy absorber. The most common function of gas struts is to raise, lower and tilt or support doors, flaps or the like and to keep these in their end positions (opened/closed). The force of the gas strut thus acts against the weight force of the application so that the force expenditure of the operator is greatly reduced. Considered from a purely physical perspective, the gas strut stores some of the energy released while lowering a part, which is then released again when raising, which ultimately "helps" the operator. Dampers, on the other hand, are used in applications where the movement or vibration of a weight or body must be braked or reduced. Like a gas strut, a damper also has a piston that divides the interior of the damper tube into two chambers. These chambers are usually filled with oil. When displacing the piston rod, the oil has to be pressed through the piston via a special connection channel. Depending on the design of the connection channel, the oil can be pushed through more easily or with more difficulty. This resistance "results" in the damping force, which always counteracts the movement direction of the piston rod and increases with an increasing movement speed of the piston rod. Considered from a purely physical perspective, a damper absorbs the movement energy of an application or converts this into heat, thus ensuring for a higher level of comfort in the application. Of course there are many practical applications that require both the force-assisting and damping function in one product. SUSPA gas struts with various damping properties (damping in retraction or extension direction or in both directions or the end position damping) are designed in such cases.

  • 13. What is a lockable gas strut?

    Like Liftline gas struts, Lockline gas struts have a piston that divides the interior of the pressure tube into two chambers. Unlike the Liftline gas strut, there is a valve in the connection channel between the two chambers that can be opened and closed from the outside. The valve makes it possible to close the connection channel in any piston rod position. When the valve is closed, the gas can no longer flow between the two chambers. This means: The piston rod is locked in this position. If the two chambers are filled with gas, the locked piston rod can be displaced by high external forces. In this case, the gas is compressed in one of the two chambers and expanded in the other. If the external forces no longer act on the piston rod, then it very quickly moves back to the position in which the valve was previously closed. This is called elastic locking. Special structural designs make it possible to achieve a rigid locking of SUSPA gas struts.

  • 14. How long is the service life of a gas strut?

    The general service life of SUSPA gas struts is between 10,000 and 100,000 double strokes (1x retraction and extension) depending on the type of gas struts. At SUSPA, the service life is tested according to internal test standards. These test standards provide for an optimal installation of gas struts. After the service life tests are completed, only a minimum power loss from escaped gas is tolerated at SUSPA. However, the actual service life of a gas strut in application depends on many factors. That is why gas struts should be tested in the respective application under the actual conditions to be able to make a reliable statement about the service life of the gas strut.

  • 15. What conditions affect the service life of gas struts?

    The most important criterion is the installation position of the gas strut with the piston rod facing down. This permanently ensures the lubrication of the piston rod seal. The frequency of the actuation also has a very decisive influence on the service life. The attachment of the gas strut may not cause any lateral load on the piston rod. In the case of lateral forces, there is a unilateral, significantly higher wear on the piston rod, guide and seal. In addition, the piston rod may not become dirty or scratched. Extremely high or low temperatures and strong vibrations in the application also lead to a reduction of the service life of a gas strut. Due to these different influences, a careful review of all factors is necessary to achieve an optimal service life of the gas strut and thus the functional suitability of the entire application. 

  • 16. What properties of the gas strut spring change with its age?

    When a gas strut is optimally installed, the moving parts experience normal wear at the points of contact. This changes the surfaces, which allows the friction to rise slightly between the moving parts. To reduce the friction and wear, the gas struts are filled with a small amount of oil, which lubricates the sealing and sliding surfaces. Like any liquid, oil has the property that it can dissolve a larger amount of gas in it under pressure than under atmospheric pressure without changing its volume. If the pressure in the liquid is reduced, this cannot dissolve as much gas and gas bubbles form in it, which rise to the surface. This effect can be seen particularly well when opening a bottle of mineral water. The oil saturated with gas inside the gas strut wets the surface of the piston rod. When sliding past the seal, a very thin film of saturated oil remains on the piston rod, which then releases the dissolved nitrogen outside of the gas strut into the atmosphere.
    In this way, some nitrogen molecules are "smuggled" out of the gas strut every time it extends and thus the gas volume and the pressure in the gas strut reduce, which ultimately results in a loss of power. If you omit the oil to prevent this effect, the wear on the seal increases so much that this no longer has a sealing effect already after a few load changes and the gas escapes. Even if the piston rod is not moved, gas struts lose pressure over time due to gas molecules that penetrate the seal. This effect is called permeation and can be reduced if the gas strut is installed and/or stored with the piston rod facing down so that the seal is not in direct contact with the gas filling, but rather is covered by the filled oil.

  • 17. What needs to be taken into consideration when using gas struts?

    SUSPA gas struts should always be installed according to our installation instructions:
    1. Install the gas strut with the piston rod facing down wards to ensure the optimal lubrication of the seal.
    2. No lateral forces may act on the piston rod in order to avoid a unilateral and therefore higher wear. When using SUSPA gas struts of the Liftline model, lateral forces can be excluded by using ball joints to fasten the gas struts. The centric force introduction must be structurally ensured when using other connection parts (e.g. eye or fork head). In the process, the axes of the eye holes and the middle axis of the gas strut must intersect and the fastening bolts must be perpendicular to the middle axis of the gas strut in every position of the application.
    3. The piston rod is to be protected from impacts, dirt and scratches. These factors increase the wear tremendously on the one hand, and on the other hand dirt particles and scratches on the sealing surfaces cause leaks.
    4. The application temperature from -30°C to +80°C should not be exceeded or fallen below, because the sealing materials wear too quickly outside of this range on the one hand, and on the other hand no longer have the necessary elasticity. Within this temperature range, the change in the extension force must be taken into consideration in order to ensure the application function for all occurring temperatures.
    5. Strong vibrations reduce the service life of gas struts. Furthermore, the maximum possible extension force must be chosen during installation, because all gas struts "lose" force during use. This can ensure that the application has a maximum functional duration.

  • 18. Should gas struts be installed with the piston rod facing up or down?

    In general, gas struts should be installed with the piston rod facing down to ensure the piston rod seal is lubricated and to reduce the permeation of nitrogen through the seal. However, the opposite installation may be necessary in some special cases, for example if the gas strut requires a very specific damping characteristic. In such cases, the lubrication of the piston rod seal must be ensured by special measures (space mat). 

  • 19. Does a gas strut have to be maintained?

    No. SUSPA gas struts are equipped with a lubricant quantity during production that lasts a life time.

  • 20. Can gas struts be repaired?

    No. All SUSPA gas struts and dampers are by a plastic deformation of the external tubes during production. This makes it impossible to open the gas strut to replace individual components without destroying it. 

  • 21. How do you find the right gas strut for a specific application?

    The function of the entire application is always the focus at SUSPA. If you know the requirements profile of your application (e.g. opening a flap, holding the flap in both end positions, automatic opening, closing by a defined manual force at a defined handle, weight of the application), it still needs to be clarified in what area it is possible to fasten the gas strut. The exact mounting points must then be determined with this data and a suitable gas strut must be defined. This process, however, proves to be very complex and usually involves a tremendous amount of research and time. That is why we offer you the implementation and selection of a suitable gas strut for you to take over. Simply sketch us the application specifying the rotation point, the weight and the desired opening angle. Furthermore, the sketch should include the location of the center of gravity and the area in which a gas strut attachment is possible. Our experienced employees will use special software to determine an optimal gas strut for your application and make you a sketch with the installation dimensions.

  • 22. How long can the gas struts be stored?

    The storage of SUSPA gas struts has no negative consequences on their function if it is ensured that the piston rods point down and no dirt accumulates on the piston rod. If gas struts are not actuated for a long time, they only have a slightly increased amount of friction during the first retraction. However, this effect is equalized after the first actuation and the gas strut then again exhibits the usual friction values.

  • 23. Does the temperature affect the function of gas struts?

    Yes. However, three temperatures ranges must be distinguished between. Between -30°C and +80°C (operating range), the temperature only affects the pressure of the gas in the gas strut. The pressure increases / decreases in this range and therefore so too does the extension force of the gas strut by about 3.5% per 10°C of the temperature rise / fall. Below the operating range, the elasticity of the sealing materials used decreases so that the surface pressure distribution in the sealing points is no longer optimally adjusted. If the temperature rises significantly above the operating range, a higher wear results on the dynamically stressed sealing points, such as the piston rod seal, due to the softening of the sealing material. The temperature has an additional effect on the damping behavior of the gas struts. The temperature increase makes the oil be less viscous, which reduces the oil's resistance to the flow of the piston. This results in less damping. Likewise, the damping increases with a lowering temperature.

  • 24. What is a soft-stop gas strut?

    Soft-stop gas struts do not have the same "damping" across the entire stroke like standard gas struts (also see 10). With this gas strut type, the "damping" also continuously increases while the piston rod is being extended, whereby its extension speed reduces consistently. Unlike standard gas struts, the connection channel between the two chambers in soft-stop gas struts is not in the piston, but rather is formed by a groove in the inner surface of the pressure tube. The gas then flows through this groove past the piston when the piston rod is displaced. The "damping" of the gas strut is determined by the cross-section of the groove at the respective piston position. The groove is designed so that its depth and therefore also the cross-section across the range of movement of the piston is not the same, but rather reduces in the direction of extension. Applications that are equipped with soft-stop gas struts are characterized by a very convenient operation and high sense of value, because the movement is gently braked once the end position is reached.

  • 25. What does Space-Mat mean?

    Space-Mat is a special lubrication system for gas struts developed by SUSPA. SUSPA gas struts equipped with Space-Mat can be mounted with the piston rod facing upwards without any problems without causing increased wear of the piston rod seal. in addition, the Space-Mat system greatly reduces the 'breakaway force" of the piston rod during the movement start, whereby the operating comfort and the sense of value of the entire application increases.