Abstract: An assembly for sealing and centering a piston rod (3) at its point of penetration in a two-cylinder dashpot or two-cylinder telescoping leg. The assembly seals and centers it as the piston rod travels into and out of the dashpot. The assembly is provided with at least one seal (13) outside the dashpot, toward the inside with at least one piston-rod sealing ring (7), and with at least one channel between them. The channel extends into a gas accommodating space (19) left between the dashpot's outer cylinder (1) and its inner cylinder (2). The gas channel is provided with a checkvalve. One object is components that eliminate the need for a high-pressure sealing ring in contact with the piston rod. Another object is a simpler checkvalve in the overflow channel. The gas channel upstream of the gas-accommodating space is provided with a flow-controlling diaphragm (22).