How gas springs work
If the piston rod of a gas spring is pushed into the pressure tube, then the content of the tube - air or another gas - is compressed (SUSPA gas springs use nitrogen of a specific purity), thus increasing the gas pressure with the result that an overpressure is created.
For if the piston fitted to the piston rod is pushed into the cylinder, the gas volume drops in two sections of the pressure tube; these two sections are connected to one another via the balance hole in order to reduce the volume coming from the cross-section and the stroke of the intruding piston rod.
Since the gas volume is contained on all sides, the pressure increases in a flat hyperbola in accordance with Boyle Mariotte's classic law. When the external force on the piston rod is removed, the overpressure drives the piston rod back to the original position. This means that the internal pressure pushes the piston rod of the gas spring outwards against atmospheric pressure.
The extension force of a gas spring is the difference between the relevant internal pressure and atmospheric pressure acting on the piston rod's cross section. The extension force of the gas pressure spring depends on the factors given below:
- On the gas pressure resulting from the compression ratio. In other words, with a slow compression of 1/10 of the original volume for example, the gas pressure increases tenfold.
- On the cross section equal to the circular surface of the piston rod that acts on the gas pressure.
If a higher extension force is wanted for a gas spring, given the same mechanical dimensions, the gas pressure in the pressure tube must be increased. Irrespective of any increase in gas pressure by compression, the pressure tube can be filled with a gas overpressure. To ensure that the cylindrical piston rod is not driven out of the tube in this process, SUSPA gas springs are secured with appropriate guides and retaining rings so that it is impossible for the piston rod to come out of the tube under overpressure.
Moreover, the guide is a precision component on which the seal tightness of the gas spring (along with the seal) also depends to a certain extent. If the piston rod is not controlled with very small clearance tolerances, one side of the piston rod touches against the seal because of the gas forces and external forces, a fact that stresses the seal accordingly in the long run and negatively affects the gas spring's service life. That is certainly one more reason for going with SUSPA when it comes to gas springs.
Selecting gas springs
When selecting the suitable gas spring from SUSPA, the following facts should be borne in mind:
- The ratio of the diameter of the piston rod to the tube determines the force level of the spring characteristics. Flat spring characteristics demand a small piston rod diameter and a large tube cross section.
- A longer stroke means smaller forces required by the gas spring and, as a result, smaller reaction forces on the link points.
- In the case of extremely long strokes, coupled with high extension forces, a larger piston rod diameter should be chosen. This solution offers greater safety against the gas spring buckling. Accordingly, the effect of transverse forces on the gas springs can generally be avoided.
Given their inherent design and by virtue of their reliability, SUSPA gas springs meet the highest requirements in a wide range of applications. But the testing of their suitability for the respective application is the responsibility of the user. We shall be pleased to support you with the selection of the suitable SUSPA gas spring and with its proper installation.