This spring is mostly used to balance a weight. In the normal position, the piston rod of the gas pressure spring is always extended. The gas pressure on both sides of the piston in the gas pressure spring is the same. The gas is compressible. When an external force is applied to the piston rod towards the cylinder, the piston compresses the gas. Due to the penetration of the piston into the cylinder, the gas pressure increases. When the external force decreases, the piston returns to its original position.