Seals are the barrier between pressurized areas in a hydraulic cylinder and are in direct contact with the movable parts (piston rod and piston). The seals create friction forces that act against the movement and decrease the energy output. But it’s not only the energy output that suffers under increased friction; the operating temperatures are also higher, resulting in the decreased service life of the whole hydraulic sealing system. Furthermore, the increased temperature influences the properties of the lubricant, espe-cially the viscosity of the oil, which results in a decreased lubrication behavior and less energy output. Apart from this, fluctuations in friction, known as stick-slip, can influence the exact positioning and/or create noise.
Sustainability – a word that is becoming more and more important – has reached nearly every area around the world. A sustainable hydraulic system must be free of leakage, but also the interval between maintenance stops must be extended to the longest possible time period. From the seal point of view this can be reached by selecting the best possible sealing system – consisting of rod and piston seals as well as guide elements and static seals – to reach the greatest efficiency. Therefore not only must the seal types themselves be understood but also the interactions between those different seal types must be well known to reach the target of a highly efficient sealing system.
This article focuses on rod sealing systems used in hydraulic applications (e.g., excavators). In particular, the interactions between the buffer and the primary rod seal were thoroughly investigated at in-house test rigs and in FEA studies. The outcome of these investigations resulted in two new friction-optimized buffer seals from SKF.
The rod sealing system in a hydraulic cylinder typically includes a buffer seal, a primary rod seal and a wiper (fig. 1).