Pneumatic piston seals are installed on the piston of a pneumatic cylinder and provide a seal between the piston and the cylinder bore. In double-acting cylinders, they help separate the two pressure chambers so that compressed air can build up on either side of the piston.
The correct piston seal contributes to efficient, reliable and smooth cylinder movement. Techniparts supplies pneumatic piston seals in a wide range of profiles, materials and dimensions. Solutions are also available for non-standard sizes, existing seal types and custom applications.
A pneumatic piston seal, also known as a piston sealing ring, is fitted to the piston inside a pneumatic cylinder. Its outer sealing surface runs along the cylinder bore and restricts unwanted air flow between the chambers on either side of the piston.
In a double-acting cylinder, the pressurised side changes as the piston moves. The piston seal must therefore maintain the necessary pressure difference so that the cylinder can generate force and move in a controlled manner.
The outside of the seal remains in contact with the cylinder wall. Sufficient contact pressure is required to minimise leakage, while friction must remain low enough for smooth pneumatic movement.
When compressed air is supplied to one side of the piston, a pressure difference is created. This pressure moves the piston and piston rod through the cylinder. The piston seal limits internal air leakage and helps maintain the pressure required for movement.
Pneumatic cylinders generally operate at much lower pressures than hydraulic cylinders. Low friction is therefore especially important. Excessive seal resistance can reduce cylinder speed and can lead to irregular movement at low speeds.
Seal profile, material, lubrication and cylinder-bore quality all influence sliding behaviour. Selecting the correct combination helps reduce leakage, wear and stick-slip.
A worn or damaged piston seal can allow compressed air to pass internally from one cylinder chamber to the other. This reduces the pressure difference across the piston and can affect cylinder performance.
Internal leakage can reduce the force available from the cylinder. Under heavier loads, the cylinder may move more slowly or may no longer reach its intended end position.
If a cylinder is stopped midway and the piston gradually changes position, internal leakage past the piston seal may be one possible cause.
A continuous airflow at an exhaust port while the cylinder is stationary can indicate that compressed air is leaking from the pressurised chamber to the opposite side. Other valves or components can produce similar symptoms, so the complete pneumatic circuit should also be checked.
When selecting a pneumatic piston seal, it is important to determine from which direction the seal will be pressurised.
A single-acting piston seal is primarily designed to seal pressure from one direction. It is commonly used in single-acting cylinders where the return movement is generated by a spring, gravity or an external force.
In a double-acting pneumatic cylinder, pressure is alternately applied to both sides of the piston. Depending on the cylinder design, a double-acting profile or two opposed single-acting seals may be used.
Pneumatic piston seals are manufactured from different elastomers and engineering plastics. The correct material depends on temperature, friction, speed, lubrication, media and the required service life.
PU combines high wear resistance with good mechanical strength and dimensional stability. It is therefore widely used for dynamic seals in modern pneumatic systems.
PTFE offers very low friction and is particularly suitable where smooth movement and low stick-slip are required. PTFE sealing elements can be combined with an elastomer energiser.
NBR is commonly used in combination with many oils and greases. HNBR can be selected when higher temperature resistance, strength or improved ageing resistance is required.
FKM/FPM, commonly known as Viton®, is used where increased temperature resistance or chemical resistance is required.
EPDM performs well with water, steam and many cleaning agents. It is generally unsuitable for mineral oils and greases, so compatibility with the lubricant must always be checked.
Correct lubrication helps reduce friction and wear between the piston seal and the cylinder wall. Depending on the seal profile and cylinder design, a suitable grease may be applied during assembly.
Always make sure that the lubricant is compatible with the seal material. This is particularly important with materials such as EPDM, which can be affected by certain mineral oils and greases.
During an overhaul, inspect the cylinder bore for scratches, scoring and other damage. A damaged running surface can quickly wear a new piston seal and cause renewed internal leakage.
The cylinder bore, piston dimensions and seal groove must be considered when identifying the correct pneumatic piston seal. Three dimensions are particularly important for many common profiles.
The outside diameter D corresponds to the sealing surface that runs against the cylinder wall and is selected to suit the cylinder bore.
The inside diameter d is determined by the piston and the diameter at the bottom of the seal groove.
The height H is measured in the axial direction of the cylinder and must match the available groove width and selected profile.
Used seals can be worn or permanently deformed. If possible, measure the cylinder bore and groove directly rather than relying only on the old seal dimensions.
Many pneumatic cylinders contain a magnetic ring on the piston. External sensors can use this magnet to detect the piston position without direct mechanical contact.
During disassembly, note the original position of the magnetic ring and inspect it for damage. It is also advisable to record the order and orientation of the seals and other piston components before removal.
Pneumatic guide strips or other guiding elements can support the piston and reduce direct metal-to-metal contact. These components should also be inspected when overhauling the cylinder.
Pneumatic piston seals are used in cylinders throughout industrial machinery, production equipment and automated systems.
Pneumatic cylinders are widely used in assembly lines, handling equipment and conveyor systems for positioning, clamping, lifting and moving components.
Pneumatic piston seals are also commonly found in packaging machinery, printing equipment, food-processing machines and other production systems.
Piston seals and rod seals are both essential components of pneumatic cylinders, but they perform different sealing functions.
The piston seal is mounted on the moving piston and limits internal air leakage between the different cylinder chambers.
A pneumatic rod seal seals around the moving piston rod and helps prevent compressed air from escaping from the cylinder.
A pneumatic wiper is often installed further outside to remove dirt from the piston rod before it retracts into the cylinder.
Techniparts supplies pneumatic piston seals from various manufacturers and can assist with identifying existing seal types. Identification can be based on the type number, profile, material and dimensions.
Techniparts is a Preferred Partner of Freudenberg Sealing Technologies and has access to various sealing profiles for pneumatic applications. Suitable alternatives can also be found for seals from other manufacturers.
Custom-made piston seals can be an option for older machinery, special cylinders and non-standard dimensions. Where possible, provide the cylinder bore, groove diameter, groove width, preferred material and operating conditions.
In addition to the piston seal, a pneumatic cylinder contains several other sealing and guiding components. It is therefore advisable to inspect the complete sealing system during an overhaul.
View our pneumatic rod seals for sealing around the moving piston rod.
Pneumatic wipers help remove contamination from the piston rod before it enters the cylinder.
Pneumatic guide strips can be used to support and guide moving cylinder components.
A pneumatic piston seal is installed on the piston and helps prevent unwanted compressed-air flow between the cylinder chambers.
Possible symptoms include loss of force, cylinder drift and internal air leakage. Continuous airflow through a valve exhaust while the cylinder is stationary can also indicate internal leakage.
A piston seal limits internal leakage across the piston. A rod seal seals around the piston rod and prevents compressed air from escaping externally.
Common materials include PU, PTFE, NBR, HNBR, FKM and EPDM. The correct choice depends on temperature, friction, lubrication, speed and the media present.
Important dimensions are the outside diameter (D), inside diameter (d) and height (H). Because a used seal may be deformed, measuring the cylinder bore and groove directly is often preferable.
Both versions are available. The correct design depends on the cylinder construction and the direction from which pressure acts on the seal.
Yes. Custom-made seals can be supplied for unusual dimensions, older machines and special cylinders. Provide the available dimensions, material requirements and operating conditions.
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