What is a Simmering? How to Use Shaft Seals? Complete Guide

Simmering seals, also known as shaft oil seals, are used to protect rotating components in machinery. A Simmering prevents leakage of lubricants such as oil and grease, and also blocks moisture, dust and dirt from entering the system.

Structure of a Simmering Seal

A radial shaft seal typically consists of:

• a metal insert for structural stability,

• an outer covering made of elastomer or steel,

• a sealing lip with or without a spring.

These seals are designed for applications with a shaft surface speed of up to 5 m/s.

Types of Simmering Seals

Different constructions allow Simmerings to be categorised into classes such as A, B and C, with markings including:

• S/ST/O: equipped with an additional dust lip,

• WxO/ZV: sealing lip without a tensioning spring,

• H: designed for high-pressure use,

• E/D/DUO: equipped with two sealing lips.

Simmering A

This type consists of an elastomeric outer casing, a metal insert and a main sealing lip with a spring. It is suitable for sealing rotating or oscillating shafts but does not include a dust lip.

Simmering AO

The AO type is a dual-lip seal designed for applications up to 0.3 MPa. It features an outer elastomer coating, a main sealing lip with spring and an additional dust lip. The dust lip provides effective protection against particles and dirt, significantly extending machine lifespan. It is widely used in construction equipment, agricultural machinery, electric motors, industrial gearboxes and mechanical drives.

Simmering B

A single-lip seal made of rubber reinforced with a metal ring, without elastomeric coating. This type is mainly used in power transmission systems and is not suitable for gas sealing.

Simmering BO

This version has no spring or protective outer layer. It is especially suitable for applications requiring protection from water and dust ingress.

Simmering C

This seal features a reinforced core without an outer elastomer cover. It is designed for use in large-scale machinery and environments with heavy dust exposure.

Benefits of Simmering Shaft Seals

Simmering shaft seals provide a tight seal between rotating and stationary machine components. They prevent lubricant leakage, reduce pressure, and protect against contaminants such as dirt and moisture. Common applications include:

• drive systems,

• axles,

• industrial gearboxes,

• pumps,

• electric motors,

• household appliances (washing machines, dishwashers),

• wind turbines.

Main advantages include:

• extended service life of machinery and components,

• reliable sealing in high-pressure systems,

• effective protection against lubricant loss,

• excellent barrier against external contamination.

How to Choose the Right Simmering

Key factors to consider before purchase:

• type of medium being sealed,

• operating temperature,

• pressure resistance,

• dimensions of the shaft and seal,

• direction of rotation and shaft speed.

Installing and Replacing a Simmering

Simmerings are installed to seal lubricant within rotating components and ensure long-lasting, leak-free operation. They are easy to mount and enhance overall system reliability.

The seal consists of a dynamic lip (with or without a spring), a metal reinforcement and an outer layer made of rubber or steel. Some Simmerings include a secondary dust lip to prevent contamination and moisture from reaching internal components.

How to Remove a Simmering

To remove a Simmering seal:

1. Ensure the seal is accessible from outside.

2. Insert two small hooks (e.g. bent wire) along the shaft.

3. Hook behind the seal and pull gently using flat pliers.

4. Alternatively, use a professional seal puller.

5. Avoid damaging the housing or shaft surfaces.

How to Install a Simmering Correctly

1. Remove the old seal carefully.

2. Inspect the shaft for scratches or distortion.

3. Wipe away all dirt and debris from the shaft surface.

4. Prepare a plastic guide or special installation tool and lightly oil it.

5. Ensure the new seal has no damage, cuts or cracks.

6. Press the seal into place without using a hammer or excessive force.

Should a Simmering Be Lubricated Before Installation?

Yes. Apply a thin layer of lubricant to the surfaces that contact the housing and the shaft. This improves sealing performance, eases installation and extends service life. Seals with a tensioning spring should never be installed dry.

Rubber Compounds Used for Simmering Seals

Common materials include:

• NBR (nitrile rubber): resistant to mineral oils and greases, vegetable and animal oils, aliphatic hydrocarbons and non-flammable hydraulic fluids (HSA, HSB).

• FKM/FPM (fluoro rubber): offers high mechanical resistance and durability, suitable for fluids with additives, aromatic and aliphatic hydrocarbons, and HSC-type hydraulic fluids.

• VMQ (silicone rubber): excellent resistance to mineral oils, aromatic hydrocarbons (toluene, xylene), salt solutions, ozone, and extreme temperatures.

Choosing the right material depends on the operating environment.

Why Does a New Simmering Leak?

Possible causes of failure include:

• incorrect seal type or size,

• improper material selection for the application,

• mechanical damage or wear on the shaft surface,

• contamination on the shaft or inside the seal,

• physical damage to the seal housing,

• installation without proper lubrication.

Even small leaks can lead to increased wear and eventually cause failure of key components such as the engine, gearbox, clutch or flywheel.

High-Quality Simmering Seals Available

We offer a wide selection of premium-quality Simmering seals tailored for technical and industrial needs. Contact us directly using the contact form.