Piston seals, also called piston packings, are seals that mount on a piston head. Piston heads move through the bore of hydraulic, pneumatic and engine cylinders. They fit onto the shaft with the sealing lip contacting the housing bore. The outside diameter lip seals against the bore, while the inside diameter seals to the gland, stretching to ensure a tight, waterproof seal and improving the piston’s stability.
Piston seals are considered dynamic, which means they are contained within moving walls, and radical, meaning they are squeezed on their inner and outer surfaces. They use axial movement and have an external sealing orientation and direction. Piston seals may be symmetrical, meaning they are perfectly even on both sides, or not, meaning their cross sections differ. They are made of many different materials depending on their specific application, including filled Teflon (reinforced with additives), polyurethane, nitrile, viton, silicone and nylon. The pharmaceutical, food processing, paint manufacturing, cryogenic, construction, liquid handling, mining, rubber and plastic processing, hydraulic press and automotive industries use piston seals to ensure a reliable, long lasting piston in machinery with reciprocating engines, pumps and gas compressors.
Piston seals must have exactly perfect compression or the result could be seal failure. This is avoided by choosing the appropriate seal dimensions, lubrication amount and material. They are components in single and double acting cylinders. In single acting, the seals need the thinnest lubrication film that can pass through the contact area between the seal and cylinder tube surface. There are four main types of piston seals, defined by the material they are made of. The first is chem-cast piston seals, which are designed for high heat and pressure applications. They rid the piston of hydraulic piston drift, cold flow and metal-to-metal contact. They are self-lubricating, reinforced with additives and made of thermoplastic rings. Urethane piston seals are bi-directional, durable and used because they perform well under extreme conditions for long periods of time. Teflon piston seals often contain strength additives and have many profile options, including T-seals, capped seals and engineered profiles. Finally, integrated piston seals are used to tighten clearance gaps, which improves the cylinder's performance. They are composed of a solid core and coated with a number of different materials.
