Oil Seal Types for Rotary Shafts: TG4, Split, PTFE & J-Type

Oil seals—also called rotary shaft seals, radial lip seals or rotary oil seals—are the primary barrier that keeps lubricant inside a rotating assembly while keeping dirt, water and abrasive particles out. Unlike O-rings, which seal in a groove around a static or reciprocating interface, oil seals ride directly on a rotating shaft with a flexible lip that maintains continuous contact. Choosing the wrong oil seal type for the application leads to leakage, contamination, accelerated bearing wear and unplanned downtime.

This guide compares the four most common industrial oil seal types: TG4 skeleton seals, split seals, PTFE seals and J-type seals. Each profile solves a different installation, speed, chemical or maintenance problem. Understanding the trade-offs lets engineers and maintenance teams select the right seal without over-specifying cost or under-specifying performance.

What Is an Oil Seal (vs O-Ring)

An oil seal is a single-element radial seal with three functional parts: a metal case that press-fits into the housing bore, an elastomer sealing lip that contacts the rotating shaft, and a garter spring that maintains lip contact as the elastomer relaxes over time. The lip is molded at a precise angle—typically 25° to 35° relative to the shaft axis—so that hydrodynamic pumping action returns a thin oil film to the sealed side during rotation.

An O-ring, by contrast, is a toroidal elastomer ring seated in a groove. It seals by being compressed between two surfaces. O-rings work well for static, slow-oscillating or short-stroke reciprocating applications, but they are not designed for continuous rotary shaft sealing. In rotary service, an O-ring lacks the controlled lip contact geometry, spring energization and dust-exclusion lip that make oil seals reliable. The result is higher friction, heat buildup, spiral failure and leakage.

Oil seals are specified by shaft diameter (inside diameter), bore diameter (outside diameter) and width. Common standards include ISO 6194 and DIN 3760. Standard NBR oil seals operate from approximately -40°C to +120°C, while FKM extends this to +200°C and PTFE covers -200°C to +260°C.

Oil Seal Types Comparison Table

TG4 Skeleton Oil Seals — When to Use

TG4 oil seals—also known as TC oil seals, rotary shaft lip seals or skeleton oil seals—are the default choice for the majority of rotary shaft applications. The metal outer case provides structural retention in the bore, the elastomer lip seals against the shaft, and a garter spring behind the lip compensates for material relaxation and thermal movement. A secondary dust lip on the air side excludes contamination.

TG4 and TC are functionally identical; TG4 is common in Asian and European supplier catalogs, while TC is the Parker/NAK designation. Both refer to a double-lip metal-cased rotary shaft seal with a spring-loaded primary lip. Standard TG4/TC sizes cover a wide range of shaft diameters, with common widths including 7 mm, 8 mm, 10 mm and 12 mm. Send your shaft and bore dimensions for exact cross-reference.

Use TG4 seals when:

• The shaft rotates at moderate to high speed (up to approximately 12–15 m/s surface speed, depending on size and lubrication).
• The housing is clean enough that a standard dust lip provides adequate contamination exclusion.
• The application uses mineral oil, grease or water-glycol mixtures within the NBR or FKM temperature range.
• Installation access allows the seal to be pressed into the bore and the shaft slid through the lip.

For general industrial and automotive oil service, NBR 70 Shore A is the standard lip material. Specify FKM when continuous operating temperature exceeds +120°C, when synthetic lubricants or fuels are present, or when aromatic hydrocarbons and acids would attack NBR.

Split Oil Seals — Installation Advantage

Split oil seals solve the maintenance problem of replacing a seal without removing the shaft, pulley, coupling or bearings. The seal body is split along one side or hinged so it can be opened, wrapped around the shaft and closed in the housing bore. A locking feature—such as an interlocking tongue-and-groove or clamping band—restores circumferential sealing integrity after closure.

The primary advantage is downtime reduction. In large pumps, mixers, turbines, paper machine rolls and mining equipment, removing the shaft to install a one-piece seal can take hours or days. A split seal reduces this to minutes.\n\nThe trade-off is higher unit cost and slightly more complex installation compared to a standard TG4 seal. However, the total cost of ownership is usually lower when downtime and labor are included.

Use split seals when:

• The shaft cannot be removed economically for seal replacement.
• The equipment is large enough that a split construction is practical (typically 50 mm shaft diameter and above).
• The speed and pressure are within the split seal's design envelope (generally lower than solid TG4 seals).
• The application tolerates the visible split joint, which is engineered to seal but may not match the pressure capability of a solid seal.

Split seals are available in all-rubber construction for flexibility and worn housings, or metal-cased construction for higher structural rigidity and speed.

PTFE Oil Seals — Chemical & Speed

PTFE oil seals combine a stainless steel outer case with a PTFE sealing lip. PTFE is chemically inert to virtually all industrial fluids and stable from cryogenic temperatures to +260°C. It can also run with minimal lubrication or intermittent dry contact.\n\nThese characteristics make PTFE seals the preferred choice for process pumps, chemical compressors, semiconductor equipment, cryogenic expanders and high-speed spindles. In these applications, conventional rubber seals would harden, swell, degrade or generate excessive friction.

Because PTFE has no elastic recovery, the lip is energized by a metallic garter spring or an elastomer secondary seal. Some designs bond the PTFE lip to an FKM or NBR backing ring, combining PTFE chemical resistance with elastomer elasticity for easier installation. Filled PTFE grades—with carbon, graphite, glass or MoS2—improve wear resistance, thermal conductivity and dimensional stability.

Use PTFE oil seals when:

• The sealed fluid attacks NBR or FKM, such as strong acids, caustics, solvents or certain synthetic fluids.
• Surface speed exceeds the practical limit of rubber seals.
• Dry-running or marginally lubricated conditions are expected.
• Operating temperature is consistently above +200°C or below -40°C.
• The shaft is hardened and polished to Ra 0.1–0.4 µm for long PTFE lip life.

J-Type Oil Seals — Automotive & General Rotary

J-type oil seals are all-elastomer rotary shaft seals without a metal reinforcing case. The J-shaped cross-section provides a sealing lip on the inner diameter and a flexible mounting flange on the outer diameter. Without a rigid case, the seal conforms to slightly out-of-round, worn or oversized bores where a metal-cased TG4 seal would not retain or seal properly.

J-type seals are lightweight, corrosion-resistant and easy to install by hand or with simple tools. The outer flange is retained by interference fit, a cover plate, adhesive bonding or a flange that bolts against the housing face. Because the seal body is entirely elastomer, it can accommodate larger bore tolerances and minor housing distortion.

Use J-type seals when:

• The application is low speed and low pressure.
• The housing is worn, non-standard or lacks the precision bore required for a press-fit TG4 seal.
• The equipment is legacy machinery where the original seal was a J-profile.
• Cost and installation simplicity matter more than high-speed or high-pressure capability.

J-type seals are not suitable for high-speed spindles or pressurized housings because the flexible body lacks the structural rigidity to resist distortion under centrifugal force or pressure.

Material Selection (NBR, FKM, HNBR, PTFE)

The sealing lip material determines temperature range, chemical compatibility, wear life and cost. The four most common materials are:

NBR (Nitrile) is the default for general oil service. It handles mineral oils, greases, water-glycol and hydraulic fluids from -40°C to +120°C. NBR offers good wear resistance, low cost and wide availability. It is not compatible with aromatic hydrocarbons, ketones, esters or ozone-rich environments.

FKM (Viton) extends service to -20°C to +200°C and resists synthetic oils, fuels, acids and aromatics that attack NBR. FKM is the standard choice for high-temperature engines, chemical exposure and aggressive synthetic lubricants. It costs more than NBR and has poorer low-temperature flexibility.

HNBR bridges the gap between NBR and FKM, operating from -40°C to +150°C with better abrasion, ozone and sour-gas resistance than standard NBR. It is common in automotive, oilfield and high-wear applications where FKM is overkill.

PTFE is used when chemical resistance, temperature extremes or dry running exceed elastomer limits. PTFE operates from -200°C to +260°C with near-universal chemical compatibility and the lowest friction of any solid engineering material. It requires a spring or elastomer energizer because PTFE has no elastic recovery.

How to Choose the Right Oil Seal

Start with the operating envelope: shaft diameter, rotational speed, sealed fluid, temperature range and pressure. Then match those constraints to a seal type and material. For most general-purpose rotary shafts in oil or grease, a TG4/TC skeleton seal in NBR is the correct default. Move to FKM when temperature or chemical exposure exceeds NBR limits. Choose PTFE only when rubber cannot survive the fluid, temperature or speed. Use split seals when shaft removal is impractical. Use J-type seals for low-speed, worn-housing or legacy applications.

Installation quality is as important as seal selection. Use a clean shaft with a lead-in chamfer, lubricate the lip and shaft before assembly, and press the seal squarely into the bore by the outer metal case only. A shaft surface finish of Ra 0.2–0.8 µm is recommended for rubber seals; PTFE seals require Ra 0.1–0.4 µm. For high-speed or abrasive service, a hardened shaft above 55 HRC provides the best wear life.

FAQ

Q1: What is the difference between TG4 and TC oil seals?

TG4 and TC describe the same double-lip metal-cased rotary shaft seal with a garter spring. TG4 is widely used in Asian catalogs; TC is common in North American and European references. The dimensions, tolerances and installation requirements are identical.

Q2: Can a split oil seal replace a standard TG4 seal without removing the shaft?

Yes. Split oil seals are designed specifically for this scenario. Wrap the seal around the shaft, close the joint and press it into the bore. Split seals are common on large pumps, mixers, turbines and gearboxes where shaft removal would require major disassembly.

Q3: When should I choose a PTFE oil seal over a rubber oil seal?

Choose PTFE when the application involves extreme temperatures, aggressive chemicals, high surface speeds or dry-running conditions that exceed the capabilities of NBR, FKM or HNBR. PTFE seals require a hardened, polished shaft surface for long life.

Q4: What shaft surface finish is required for oil seals?

For rubber oil seals, a shaft surface finish of Ra 0.2–0.8 µm is recommended. PTFE oil seals require a smoother finish of Ra 0.1–0.4 µm. The shaft should be free of circumferential machining marks, scratches and corrosion. Hardened shafts above 55 HRC provide the best wear resistance in abrasive or high-speed service.

Q5: What is the maximum pressure for a standard oil seal?

Standard TG4/TC oil seals are designed for essentially atmospheric or low-pressure splash-lubricated housings—typically up to approximately 0.5 bar. For pressurized housings above this range, specify a medium-pressure design such as TCV or contact the supplier for a pressure-rated lip design.

Q6: How do oil seals work?

An oil seal uses a flexible elastomer lip pressed against a rotating shaft by a garter spring. The lip angle creates a hydrodynamic pumping action that returns a thin oil film to the sealed side as the shaft rotates. A secondary dust lip on the air side keeps contamination out of the sealing zone.

Q7: What are the most common TC oil seal sizes?

TC oil seals are specified by shaft diameter, bore diameter and width. Common widths include 7 mm, 8 mm, 10 mm and 12 mm, with shaft diameters spanning a wide range from small instrument shafts to large industrial rolls. Always match the TC size to the actual shaft and bore measurements rather than guessing.

Q8: How do I cross-reference an oil seal by size?

Measure the shaft diameter (inside diameter of the seal), the bore diameter (outside diameter of the seal) and the seal width. Compare these three dimensions against the manufacturer catalog or a size chart. If the original part number is readable, the first two numbers usually indicate shaft and bore size, and the suffix indicates the profile and material.

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Related engineering resources: Oil Seal vs O-Ring: When to Use Each | Oil Seals | TG4 Oil Seals | Split Oil Seals | PTFE Oil Seals | J-Type Oil Seals