Hydraulic cylinder seals

Frequently asked questions — Hydraulic and Pneumatic Seals

• How can piston seals and rod seals be distinguished in a hydraulic cylinder?

  The piston seal, available in the PT, GP or K series, provides sealing between the two cylinder chambers during the stroke and is made from filled polyurethane or PTFE with an energiser. The rod seal, on the other hand, belonging to the UN, US or UH series, is specifically designed to seal the rod outlet to the outside. Their use therefore differs according to their functional position, with the rod seal allowing no permissible leakage to the external environment.
• Which guide rings should be selected to prevent metal-on-metal contact?

  Guide rings in the WR and FB series are designed to centre the piston within the tube or the rod within the housing. They absorb the radial loads caused by alignment errors or rod deflection. You can choose between models made from sintered bronze combined with PTFE, or from polyacetal (POM), depending on the specific mechanical constraints of your assembly, in order to prevent any degradation through direct contact.
• Which material should be favoured for seals in a pneumatic environment?

  In pneumatic applications, seals are subjected to pressures of 4 to 10 bar and high cycling frequencies. NBR with reinforcing fabric is the standard reference for these applications, operating dry or with reduced lubrication. For applications requiring very high speeds, exceeding 2 m/s, PTFE is the recommended material to ensure the durability of the system.
• What is the impact of surface roughness on seal service life?

  Bearing surface roughness is a decisive factor for the longevity of dynamic seals. It is essential to maintain a Ra roughness of between 0.2 and 0.4 µm for the rod and between 0.8 and 1.6 µm for the cylinder. Failure to observe these values, or the presence of straightness defects on the rod, leads to the premature destruction of the seals within just a few cycles.
• What is the function of a wiper seal on a cylinder rod?

  The wiper seal, identified by the A or SAS series, is fitted ahead of the rod seal. Its technical role is to block the ingress of external contaminants such as dust, swarf or liquids. It features a specific geometry with a sharp edge on the outer side for scraping, while its inner profile remains flexible to adapt perfectly to the kinematics of the moving rod.