Due to improvements in seal technology, today hydraulic systems can be designed so that they are completely leak-free. However, for seals which seal the piston rod relative to the pressure chamber, a minimal „lubricating film“ is desirable. This improves not only the gliding properties on the piston rod, but also reduces wear.

For this purpose, the special seals have a recirculation function that conveys this microfilm back to the pressure chamber. This prevents the microfilm from forming drops, and thus ensures that no hydraulic fluid escapes into the environment.

In order to achieve as long a service life as possible, the seal, microfilm and rod characteristics have to be matched to each other optimally.

Particular attention has to be paid to the rod surfaces; this can achieved in   the following ways:

  • Piston rods hardened, polished and hard chrome plated
  • Hardened and polished
  • Hardened, polished and hard chrome plated



Even extremely fine scoring on the piston rod will inevitably lead to leakage, and will significantly reduce the service life of seals. Therefore it has to be ensured that piston rods are not subjected to any external mechanical stresses – either in operation or during maintenance.



The use of hardened, polished and hard chrome plated piston rods like those supplied by AHP Merkle significantly reduces the risk of damage.



Hardened piston rod (AHP Merkle standard)

Non-hardened piston rod: