Pneumatic rod seals provide the seal between the moving piston rod and the cylinder head of a pneumatic cylinder. The seal helps prevent compressed air from leaking out along the piston rod, while allowing the rod to move freely with as little resistance as possible.
A good rod seal contributes to the efficient and reliable operation of the pneumatic cylinder. Techniparts supplies pneumatic rod seals in various profiles, materials and dimensions. Suitable solutions can also be found for non-standard sizes, existing types and special applications.
A pneumatic rod seal, also known as a piston rod seal, is installed in the cylinder head around the piston rod. The sealing lip makes contact with the moving rod and helps prevent compressed air from escaping from the cylinder into the surrounding environment.
Because the piston rod moves through the seal during every stroke, a rod seal must do more than simply provide effective sealing. Friction, wear and sliding behaviour also play an important role.
The sealing lip is pressed against the piston rod and slides over its surface as the rod extends and retracts. The seal must provide sufficient contact pressure to limit air leakage without causing unnecessary resistance.
During the movement of a pneumatic cylinder, the piston rod continuously slides through the rod seal. The sealing lip remains in contact with the surface of the rod and forms a barrier between the compressed air inside the cylinder and the outside environment.
Pneumatic systems generally operate at considerably lower pressures than hydraulic systems. Low friction is therefore particularly important. A seal that creates too much resistance can slow down the cylinder or cause irregular movement.
The correct profile and material provide a balance between effective sealing and smooth sliding behaviour. Factors such as operating pressure, speed, lubrication, temperature and the surface quality of the piston rod must be taken into account.
A leaking pneumatic rod seal is not always immediately visible. With a hydraulic cylinder, leakage may appear as oil around the cylinder. In pneumatic systems, compressed air escapes into the surrounding environment instead.
A hissing sound around the cylinder head may indicate air leakage along the piston rod. However, this may be difficult to hear in a noisy production environment.
When some of the compressed air is lost, the cylinder may move more slowly or deliver less force. This can become particularly noticeable as the load increases.
Multiple small leaks within a pneumatic system can cause the compressor to recharge more frequently. Timely inspection and replacement of worn seals can therefore help reduce unnecessary compressed-air losses.
In pneumatic cylinders, the sealing and wiping functions can be performed by separate components. Profiles are also available in which both functions are combined.
With a separate rod seal, the sealing function is separated from the wiping function. This allows a specific profile and material to be selected for each position.
A combined design can provide both sealing and wiping functions. This can be useful in compact cylinders where installation space is limited. The appropriate design depends on the cylinder construction and operating conditions.
Pneumatic rod seals are available in various elastomers and plastics. The appropriate material is determined by factors including friction, speed, temperature, lubrication, wear and the media present.
NBR is a commonly used material for general pneumatic applications and offers good properties in combination with many oils and greases.
PU combines good mechanical properties with high wear resistance. This makes polyurethane suitable for applications with frequent movement and higher mechanical loads.
PTFE has a very low coefficient of friction and can be used where smooth sliding behaviour and the reduction of stick-slip are important. Depending on the design, PTFE seals are combined with a preloading element.
FKM/FPM, often referred to as Viton®, can be used when greater temperature or chemical resistance is required.
EPDM offers good properties with water, steam and various cleaning agents. The material is not suitable for many mineral oils and greases. Always check the compatibility between the sealing material and lubricant.
Low friction is important for smooth movement in a pneumatic cylinder. Excessive resistance between the sealing lip and piston rod can slow down movement and cause irregular motion at low speeds.
Depending on the cylinder design, a suitable lubricating grease can be applied during assembly. The lubricant must be compatible with the sealing material.
Excessive friction can cause stick-slip, resulting in uneven piston rod movement. The correct sealing profile, material, lubricant and good piston rod surface quality help reduce this effect.
When the piston rod extends, it comes into contact with the surrounding environment. Dust, moisture, fibres and other contaminants can therefore settle on the surface of the rod.
To prevent these contaminants from entering the cylinder during the return stroke, a pneumatic wiper is often used.
During an overhaul, inspect the piston rod for scratches, corrosion and other damage. A damaged surface can cause a new rod seal to wear prematurely and result in renewed leakage.
The dimensions of the piston rod and sealing groove are important when selecting the correct pneumatic rod seal. For many profiles, three main dimensions are used.
The inside diameter d is matched to the diameter of the piston rod against which the sealing lip seals.
The outside diameter D relates to the dimensions of the sealing groove in the cylinder head.
The height H is measured in the longitudinal direction of the cylinder and must match the available groove width and sealing profile.
A used seal may be worn, hardened or deformed. If in doubt, measure the piston rod and groove as well instead of relying solely on the dimensions of the old seal.
A rod seal and piston seal are both used in a pneumatic cylinder, but they have different functions and installation positions.
The rod seal is located in the cylinder head and seals around the moving piston rod. Its main function is to limit compressed-air leakage from the cylinder into the surrounding environment.
The pneumatic piston seal is located on the piston and helps prevent compressed air from flowing internally from one cylinder chamber to the other.
Proper guidance of the piston rod is important for the service life of the rod seal. If the rod is subjected to misaligned or lateral loads, the sealing lip may be more heavily loaded on one side.
This can cause uneven wear and premature leakage. When problems occur with a rod seal, therefore check not only the seal itself but also the guidance, alignment and condition of the piston rod.
Pneumatic guide strips can be used to support and guide moving components.
Pneumatic rod seals are used in pneumatic cylinders in a wide variety of machines, installations and automation systems.
In production lines, assembly systems, handling equipment and conveyor systems, pneumatic cylinders are used for positioning, clamping and moving components.
Pneumatic cylinders with rod seals are also used in packaging machinery, printing equipment, food-processing machinery and laboratory equipment.
Techniparts supplies pneumatic rod seals from various manufacturers. Existing seals can be identified using information such as type number, profile, material and dimensions.
Techniparts is a Preferred Partner of Freudenberg Sealing Technologies. This provides access to various sealing profiles from Freudenberg and Dichtomatik. Suitable alternatives can also be found for existing seals from other manufacturers.
For older machines, custom-built equipment and non-standard dimensions, custom-made pneumatic rod seals can provide a solution. Where possible, provide the rod diameter, groove diameter, groove width, required material and operating conditions.
In addition to the rod seal, a pneumatic cylinder contains various other sealing and guiding elements. During an overhaul, it is therefore advisable to inspect the complete cylinder.
View our pneumatic piston seals for sealing between the piston and cylinder wall.
Pneumatic wipers can be used to protect against dirt and contamination.
Pneumatic guide strips are also available to support and guide moving components.
A pneumatic rod seal is installed around the moving piston rod and helps prevent compressed air from leaking out of the cylinder.
Possible signs include audible air leakage, slower cylinder movement, loss of force or a compressor that needs to recharge more frequently. If in doubt, also check other possible leakage points.
A rod seal prevents leakage along the moving piston rod to the outside. A piston seal helps prevent internal leakage past the piston between the cylinder chambers.
Common materials include NBR, PU, PTFE, HNBR, FKM and EPDM. The material selection depends on factors such as temperature, speed, friction, lubrication and the media present.
Important dimensions are the inside diameter (d), outside diameter (D) and height (H). If the seal is worn or deformed, preferably also measure the piston rod and sealing groove.
Excessive friction between the seal and piston rod can contribute to stick-slip. The correct profile, material, lubricant and good rod surface quality are therefore important.
For non-standard dimensions, older machines and special cylinders, custom-made rod seals can provide a solution. Information such as the rod diameter, groove dimensions, material and operating conditions is required.
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