A hydraulic cylinder seal fails quietly: a slight weep at the rod appears first, then pressure drops, and the node stops holding the load at the worst point in the cycle. A rubber cuff under high pressure extrudes into the gap and tears; a silicone seal cannot survive dynamic abrasion at all. A polyurethane seal from TIMOL holds pressure and abrasion, does not extrude into the gap, and lasts several times longer than rubber. This article explains how a polyurethane seal works, why it outperforms other materials in numbers, and how to order a cuff for your cylinder.
What a Polyurethane Seal Is and How It Works
A seal blocks the path of fluid or gas between moving or stationary surfaces: it prevents hydraulic fluid from leaking out of a cylinder and keeps dirt and moisture from entering inside. The working edge of the seal presses against the rod or bore by its own elastic force plus the pressure of the medium, and it is here that the mechanical properties of the material are decisive.
Polyurethane is suited for seals because it combines the elasticity needed for tight contact with the strength that prevents the edge from extruding into the gap. Tear resistance of 40-120 kN/m and tensile strength of 39-87 MPa mean that even under high pressure the edge holds its geometry and does not fail. This is the primary reason polyurethane dominates in hydraulic cuffs.
The cross-section profile of the seal determines its operation no less than the material. A cuff with a working lip and elastic backing self-energises with medium pressure: the higher the pressure, the tighter the edge presses against the rod. Support-guide rings of polyurethane carry lateral load and prevent the rod from touching the bore metal-to-metal. These elements are often fitted as a set, and making them from the same material is convenient for compatibility and service life. Polyurethane cuff manufacturing technology is covered in detail in the article on cuff manufacturing from polyurethane.
Why Polyurethane Outperforms Rubber, Silicone, and PTFE
Polyurethane beats other sealing materials on the combination of wear resistance, strength, and oil resistance — precisely the properties that determine seal life in a real cylinder. Each competitor is strong in one area but loses overall.
NBR rubber is oil-resistant and inexpensive, but mechanically weak: tensile strength 10-25 MPa and tear resistance 10-50 kN/m. Under high pressure its edge extrudes into the gap between rod and bore and tears. Abrasion at 80-150 mm³ is also worse than polyurethane’s 38-39 mm³, so in an abrasive environment a polyurethane cuff lasts noticeably longer.
Silicone rubber has a wide temperature range but is unsuitable for dynamic seals: abrasion of 150-350 mm³ and tensile strength of only 5-12 MPa. It is good for static gaskets in high-temperature nodes but not for a moving rod. PTFE is chemically inert and slippery, but abrasion at 200-500 mm³ is the worst in the table, and under sustained compression it creeps — the part loses its geometry over time. As an independent dynamic sealing edge it also has insufficient service life.
Material Comparison for Seals
| Material | Abrasion DIN 53516, mm³ | Operating t, °C | Tensile strength, MPa | Oil resistance |
|---|---|---|---|---|
| Polyurethane TIMOL | 38-39 | -60…+100 | 39-87 | excellent |
| NBR rubber | 80-150 | -30…+100 | 10-25 | good |
| Silicone rubber | 150-350 | -60…+230 | 5-12 | moderate |
| PTFE (fluoroplastic) | 200-500 | -200…+260 | 15-35 | excellent |
Silicone and PTFE win on the upper temperature limit, but for dynamic seals that is not decisive: their abrasion is several times worse than polyurethane, and silicone is also weak in tensile strength. NBR rubber performs better, but on strength and abrasion still yields to polyurethane by a factor of two and more. For dynamic seals under pressure and abrasion, polyurethane remains the optimal material; silicone and PTFE make sense only in narrow temperature or chemical niches.
Engineer’s tip: when selecting a seal, check not only the size but the clearance between the rod and the bore. The larger the clearance and the higher the pressure, the greater the risk of edge extrusion, and the harder the polyurethane or the stronger the support ring that is needed. Before installation, check chamfers and sharp edges in the groove: a burr cuts a new cuff during fitting. Do not stretch the seal excessively when sliding it on — polyurethane is elastic but an overstretched edge loses fitting accuracy.
Where Polyurethane Seals Are Used
Hydraulics and pneumatics are the primary application for polyurethane seals: rod and piston cuffs in cylinders of presses, hoists, and road and construction machinery work under high pressure in an oily environment, where polyurethane performs best. Wiper seals protect the rod from external dirt and moisture, extending the service life of the primary seal.
Industrial equipment uses polyurethane seals and gaskets in nodes where resistance to vibration and chemicals is important. Construction and road machinery, and utility vehicles, use polyurethane cuffs because of constant contact with abrasive and dirt that quickly destroys rubber. In agricultural machinery, where hydraulics operate in dust under cyclic load for an entire season, the durability of a polyurethane seal directly affects the number of forced field stops.
Wiper seals deserve special mention. On machinery working in dirt, a worn wiper seal admits abrasive to the rod, which quickly destroys the primary seal and polishes the rod surface. A polyurethane wiper seal with a hard edge wipes dirt more effectively than a rubber one and itself lasts longer, protecting the whole seal assembly rather than merely blocking the outer contour.
TIMOL polyurethane works in 12 industrial sectors, and everywhere pressure, oil, and wear are present, seals from this material deliver longer life than rubber. The full product range is in the product catalogue, and technical detail in the reference information section.
How to Order a Seal for Your Node
To manufacture, provide a sample of the old seal or a drawing with dimensions: rod or piston diameter, groove width and depth, cross-section profile. If there is no sample, measure the node and describe the operating conditions: pressure, temperature, fluid type, presence of abrasive. Based on this data the technologists will select hardness and edge profile.
Production is possible one-off, for the repair of a specific cylinder, and in batches for a fleet of identical equipment. The free-casting process allows even a discontinued or non-standard profile to be reproduced without expensive tooling. For consultation, selection, and ordering, contact TIMOL factory. Engineers will select a seal for your pressure and medium and produce it to the exact geometry of the node.