Oil Seal DB - Rotary Shaft Seal

Construction and Functional Principle

The DB oil seal consists of a metal outer diameter into which two separate elastomeric sealing lips are integrated. Both lips are supported by a garter spring, allowing each lip to apply a constant radial sealing force to the shaft independently. As a result, each lip functions as a fully active seal rather than as a secondary or protective lip. This configuration enables the seal to provide effective sealing on both sides of the shaft, making it suitable for separating two different media within a single shaft passage.

Applications and Why This Type Is Suitable

DB oil seals are used in rotating machine components where two media must remain separated within a single shaft passage. Typical examples include industrial gearboxes with separate lubrication circuits, drive systems in which bearing lubrication and transmission lubrication must remain isolated, and pump units where different fluids are present on either side of the seal. This type of rotary shaft seal is also used in certain reduction gearboxes, mixers, and process installations to prevent mixing of oil and grease or two different types of oil.

The suitability of the oil seal DB lies not only in the presence of two sealing lips, but primarily in the fact that both lips are functionally equivalent and actively sealing. This allows a single compact component to perform a task that would otherwise require two separate oil seals arranged back-to-back. The result is a simpler mechanical design, reduced installation space, and a lower risk of tolerance issues or assembly deviations within the sealing arrangement.

Material Options

The material selection of a DB oil seal has a significant impact on its suitability for a given application. NBR is the standard material and is suitable for mineral oils and greases across a wide temperature range. It offers a good balance between wear resistance, elasticity, and cost efficiency.

For higher temperatures or chemically more aggressive lubricants, FKM is often the preferred choice, providing greater thermal and chemical stability, even with reduced flexibility at low temperatures. ACM is suitable for oils containing additives, while HNBR is recommended for applications involving higher mechanical loads or extended service life.

Special elastomers such as silicone, CR, or EPDM are used only for specific media or temperature requirements and always require careful compatibility verification. For corrosive environments, springs and reinforcing rings can be supplied in stainless steel.

Material Table

Comparable Oil Seal Types

Within the range of oil seals, the oil seal DB occupies a clearly defined niche. Unlike SC oil seals, it is not intended for sealing a single medium, but for applications in which two media must remain separated. Compared to TC oil seals, the difference is fundamental: in a TC oil seal, the second lip functions as a dust lip, whereas in a DB rotor seal both lips are spring-supported and actively sealing.

In addition, the DB oil seal is distinguished by its metal outer diameter, which ensures stable and accurate seating in the housing. This makes it more dimensionally stable than rubber-OD variants, but also less tolerant of imperfections in the housing. As such, the oil seal DB is not a universal solution, but a targeted choice for specific sealing challenges where medium separation is the primary focus.

Selection Criteria: Dimensions, Tolerances, and Boundary Conditions

Correct selection of a oil seal DB starts with proper dimensions and tolerances. The shaft must match with ISO h11, have a minimum hardness of 45 HRC, and feature a fine surface finish to prevent wear and leakage. The shaft surface should be torsion-free and finished to a surface roughness of Ra 0.2–0.8 μm, Rz 1–5 μm, with a maximum Rmax ≤ 6.3 μm to ensure reliable sealing and minimal wear. For the housing bore, a tolerance of ISO H8 is recommended, with a surface roughness of Ra 0.8–3.2 μm, Rz 6.3–16 μm, and a maximum Rmax ≤ 16 μm, particularly important for seals with a metal OD. The housing should be manufactured to ISO H8 tolerances and provide a smooth surface for a reliable metal-to-metal press fit.

In addition, operating temperature, type of medium, circumferential speed, and pressure play a decisive role. For standard material combinations, the DB oil seal is designed for operating temperatures from –40 °C to +100 °C, with a recommended maximum continuous temperature of +80 °C, a maximum pressure of 0.02 MPa, and a circumferential speed of up to 5 m/s, depending on operating conditions. DB oil seals are intended for pressureless or very low-pressure applications and have a limited maximum circumferential speed. When synthetic lubricants or non-standard media are used, material compatibility must be verified in advance.

Oil Seals are produced in different factories. The different factories and suppliers therefore use their own product names for the Oil Seals for the different types. Find the cross reference of different oil seal factories/suppliers in the table below:

Cross Reference

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