Pneumatic wipers, also known as scrapers, wiper rings or rod scrapers, remove dirt, dust, fibres and moisture from the piston rod of a pneumatic cylinder. When the rod retracts, the wiper helps prevent contamination from entering the cylinder head and damaging the seals behind it.
Pneumatic cylinders generally operate at relatively low pressure and high speeds. This makes low friction, smooth sliding behaviour and effective wiping especially important. Techniparts supplies pneumatic wipers in various materials, profiles, brands and sizes, both metric and inch.
A pneumatic wiper is installed around the piston rod at the outer side of a pneumatic cylinder. The wiping lip runs along the rod and removes contamination before it can enter the cylinder during the inward stroke.
This not only helps keep the inside of the cylinder clean, but also protects the pneumatic rod seal and other internal components against contamination and premature wear.
Dust, moisture and other particles on the piston rod can be carried past the seals when the rod retracts. A correctly selected wiper therefore forms the first line of defence against contamination of the pneumatic cylinder.
Although pneumatic and hydraulic wipers perform the same basic function, their operating conditions differ significantly. Pneumatic cylinders generally operate at lower pressures and under drier conditions than hydraulic cylinders.
In pneumatic systems, compressed air is the working medium. As a result, the continuous oil film that may be present in a hydraulic application is often absent. A wiper lip that presses too firmly against the rod can therefore cause unnecessary friction.
When selecting a pneumatic wiper, not only wiping performance and wear resistance should be considered, but also sliding behaviour, speed and the risk of stick-slip.
The design of the groove in the cylinder head determines which type of wiper can be installed. A wiper designed for an open bore is not automatically suitable for a closed groove, and vice versa.
In a closed groove, the wiper is installed in a chamber enclosed on both sides. This construction is commonly used in pneumatic cylinders.
With an open groove or bore, the wiper is installed from the outside. Designs with a metal core or outer casing can be used here and are retained in the bore by means of a suitable interference fit.
In pneumatic cylinders, wiping and sealing can be performed by separate components. Combined profiles are also available in which both functions are integrated into a single element.
With a separate wiper, the most suitable material and profile can be selected individually for the wiping function and the rod seal. This provides additional flexibility under demanding or specific operating conditions.
A combination wiper combines the functions of a wiper and rod seal. This can be particularly useful in compact pneumatic cylinders where installation space is limited.
Pneumatic wipers are available in various elastomers and engineering plastics. The correct material depends on friction, wear, temperature, speed, lubrication and the environment in which the cylinder operates.
NBR is widely used in general pneumatic applications. It combines good elastic properties with an attractive price and good resistance to many oils and greases.
PU offers high wear resistance and good mechanical properties. It can therefore be a suitable choice for cylinders with frequent movement or applications where a long service life is important.
PTFE has a very low coefficient of friction and can be useful at high speeds, with dry compressed air or where stick-slip must be minimised. Depending on the design, PTFE profiles can be energised by one or more O-rings.
FKM/FPM, commonly referred to as Viton®, can be used where higher temperatures or improved chemical resistance are required.
EPDM performs well with water, steam and various cleaning agents. However, it is unsuitable for many mineral oils and greases. Always check the lubricant and operating medium before selecting the material.
The wiping lip must make sufficient contact with the rod to remove contamination without creating excessive resistance. Especially in pneumatic cylinders operating at low pressure, excessive friction can immediately affect cylinder performance.
If static friction is too high, the piston rod can initially remain stationary and then suddenly start moving. This phenomenon is known as stick-slip and can cause jerky or irregular cylinder movement.
Many modern pneumatic cylinders are lubricated for life. If additional lubrication is used, the lubricant must be compatible with the wiper and the other seals in the cylinder.
The operating environment has a major influence on the choice of pneumatic wiper. In a dry production environment, removing dust and fibres may be the main requirement, while in wet or hygienic environments chemical resistance can be more important.
In the food industry, cylinders may regularly be cleaned with water, detergents or disinfectants. The temperature, chemical resistance and any specific material requirements should therefore all be considered.
For outdoor use or refrigerated environments, low temperatures, moisture and weather exposure must also be considered. The correct material is important to maintain flexibility of the wiping lip.
Four important dimensions are generally required to select the correct pneumatic wiper: the inside diameter, outside diameter, installation height and overall height.
The inside diameter d is matched to the diameter of the piston rod over which the wiper lip runs.
The outside diameter D is determined by the groove or bore in which the wiper is installed.
The installation height h indicates the section that is actually installed in the groove or bore.
The overall height H also includes the section of the profile that protrudes outside the groove. Because a used wiper may be deformed, it is often advisable to measure the piston rod and mounting groove directly as well.
With standardised pneumatic cylinders, important dimensions can often be determined from the cylinder type and bore size. This can make selecting the correct wiper easier.
ISO 15552 and ISO 6432 are used for various standardised pneumatic cylinders. If the cylinder type is known, the rod and bore dimensions can often be determined from the applicable standard or the manufacturer's specifications.
A worn wiper may no longer remove sufficient contamination from the piston rod. Dirt can then enter the cylinder along the rod and damage other components.
Check the wiping lip for cracks, cuts, hardening and uneven wear. A damaged lip may no longer make contact with the piston rod around its entire circumference.
Increasing contamination around the cylinder head or piston rod can indicate insufficient wiping performance. Also check the condition and alignment of the piston rod.
A wiper can only operate evenly when the piston rod is properly guided. Side loads or misalignment can place more stress on one side of the wiping lip.
This can cause uneven wear and reduce service life. If problems occur, also inspect the pneumatic guide strips and other guiding components.
Also inspect the piston rod for scratches, corrosion and damage. A damaged rod surface can accelerate wear of both the wiper and the rod seal.
Techniparts supplies pneumatic wipers from various manufacturers. An existing wiper can often be identified by its type number, dimensions, profile and material.
This often makes it possible to find an original type or a technically equivalent alternative for existing cylinders, even when a particular type number is no longer produced as standard.
For older machines, inch sizes and special cylinders, custom pneumatic wipers may provide a solution. If possible, provide the rod diameter, groove diameter, installation height, overall height, material and operating conditions.
During an overhaul, it is advisable to inspect the other sealing and guiding elements of the pneumatic cylinder in addition to the wiper.
View our pneumatic rod seals for sealing around the moving piston rod.
Pneumatic piston seals are available for sealing between the piston and cylinder wall.
Pneumatic guide strips can also be used to support the moving components.
A pneumatic wiper removes dirt, dust and moisture from the moving piston rod before it enters the pneumatic cylinder.
Not automatically. A hydraulic wiper may have higher lip pressure and therefore more friction. Pneumatic applications generally require low resistance and smooth movement.
Stick-slip may be one possible cause. Excessive friction from seals, wipers or guiding elements can make the rod stick initially and then move suddenly.
Common materials include NBR, PU, PTFE, FKM and EPDM. Depending on the application, polyester, POM, UHMW-PE or versions with a metal casing can also be used.
Important dimensions are the inside diameter (d), outside diameter (D), installation height (h) and overall height (H). With a worn wiper, also measure the rod and mounting groove if possible.
Replacement is advisable in the event of cracks, hardening, a worn lip, uneven wear or increasing dirt accumulation around the piston rod.
The wiper keeps contamination outside the cylinder. The rod seal helps prevent compressed air from escaping along the piston rod.
Yes. For older machines, inch sizes and non-standard cylinders, custom-made pneumatic wipers or technically suitable alternatives can be supplied.
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