Piston Hydraulic Seals

Piston hydraulic seals are critical components in hydraulic cylinders that create a seal between the piston and the cylinder bore to prevent fluid leakage and maximize system efficiency. They contain the pressure on one side of the piston, which enables the conversion of fluid power into linear motion.
Hydraulic Cylinder Piston Seal Types - TYS Seals
Piston seals - double acting hydraulic cylinder piston seals ...
Complete Hydraulic Seal Kit - Including Rod, Piston, O-Ring ...
Function and Design
Piston seals are dynamic seals that manage the movement and pressure within a hydraulic cylinder.
Pressure Containment: Their primary function is to block or separate the hydraulic fluid in reciprocating motion applications, ensuring that pressure builds up on one side of the piston to drive movement.
Efficiency: A properly functioning seal is vital for system efficiency; leakage past the piston would lead to a reduction in performance and potential system damage.
Dynamic Motion: They maintain sealing contact with the cylinder bore as the piston moves, a challenging dynamic environment that requires durable materials and precise design.
System Protection: While their main role is sealing the fluid, they also allow a minimal layer of lubrication to prevent corrosion on internal components.
Single-Acting vs. Double-Acting
Piston seals are classified based on the direction from which pressure is applied.
Single-Acting Piston Seals:
Designed for cylinders where pressure is applied only from one direction.
They are required to retain pressure from that single direction, enabling the piston to move in a "single action".
The seal must leave a minimum oil film when passing along the bore to prevent external leakage, as the non-pressure side may be open to atmosphere and draw in contaminants.
U-cup seals are a common type of single-acting piston seal.
Double-Acting Piston Seals:
Designed to withstand fluid pressure from both directions.
They have a symmetrical cross-section and identical sealing functions for movement in both directions (in and out).
These are used to drive the piston in both directions or hold it in a controlled position.
Double-acting seals often consist of a slide ring and an energizer (like an O-ring or X-ring) to ensure sealing in both directions.
Materials
Material choice is essential due to high pressures, temperatures, and chemical exposure.
Polyurethane (PU): A very common material, known for high mechanical strength, excellent abrasion resistance, good elasticity, and resistance to hydrolysis.
PTFE (Polytetrafluoroethylene): Used in high-temperature or corrosive fluid environments, offering very low friction and high chemical resistance. PTFE seals are often part of a composite seal assembly with an energizer and anti-extrusion rings due to their high extrusion risk.
Nitrile Rubber (NBR): A general-purpose elastomer with good resistance to petroleum-based fluids like hydraulic oils and greases.
Polyamide (PA): Used for strength, rigidity, and good wear resistance, often in combination with other materials or as guide rings and anti-extrusion elements.
Common Applications
Piston hydraulic seals are used in a variety of industries where fluid power is converted into linear motion.
Construction Equipment: Widely used in machinery such as excavators, bulldozers, and tractors.
Agricultural Machinery: Essential for the operation of equipment like combine harvesters.
Industrial Machinery: Found in hydraulic presses, forming machines, and various plant machinery.
Mobile Hydraulics: Utilized across mobile applications where force and control are needed.
Offshore and Maritime: The robust nature of the seals makes them suitable for marine environments.