Damping Inserts in Manhole Cover Assemblies

Damping inserts play a crucial role in manhole cover–frame assemblies. They help minimize noise, ensure stability, and extend the lifespan of the entire system. In this article, we will look at why they exist, the materials available, design solutions, and recommendations for their use in both heavy traffic and less demanding environments.

Why Do Damping Inserts Exist?

Damping inserts are designed to be placed between the contact surfaces of the cover and the frame of a manhole. Their main functions are:

Noise reduction – eliminating unpleasant sounds when vehicles pass over the cover.
Cover stabilization – limiting micro-movements, rattling, and impacts.
Assembly protection – reducing wear on contact surfaces, thereby extending the lifespan of the manhole cover system.

Without a high-quality damping insert, noise, vibrations, and faster wear of both the cover and the frame may occur. This can lead to more frequent repairs and warranty claims, increasing overall operating costs.

Types of Materials and Their Properties

The material of the damping insert significantly affects its performance and durability. The materials used include PUR, EPDM, composites, and plastics. The most common types on the market include:

Plastic / Composite

Properties: Low-cost solution suitable only for low loads.
Disadvantages: Short lifespan, rapid deformation (compression), limited durability.
Typical use: Low-load environments; generally not recommended for heavy or intensive traffic.

Rubber (Elastomer)

Properties: A good solution for standard loads; performance depends on the composition of the rubber compound. A typical example is EPDM rubber.
Disadvantages: Poor design or low-quality compounds can lead to rapid degradation.

Polyurethane (PUR)

Properties: A premium solution with high resistance to wear and long-term stability.
Advantages: Ideal for heavy traffic, long service life, high comfort.
Typical use: Recommended for traffic loads from class D400 and above.

Damping Insert Design

However, the material alone does not determine the final performance. A damping insert should be designed to damp across the largest possible area – only then can it reliably ensure cover stability and minimize noise.

EPDM damping insert

We use the EPDM damping insert mainly for foreign markets. A groove is milled into the frame, and the EPDM rubber is inserted into it.

KASI PUR damping insert

We apply the PUR damping insert onto the casting robotically in liquid form in order to level out the irregularities that occur during casting. To achieve perfect flatness, we CNC-machine both frames and covers around the entire circumference.

Typical Failures in Low-Quality Solutions

Cheap or poorly designed damping inserts can cause several issues:

Insert compression: Loss of height causes the cover to “settle,” bringing back noise and impacts.
Mechanical damage
Secondary assembly damage: Faster wear of the frame and cover, which may eventually require complete replacement.

Recommended Applications

Damping inserts are essential in certain environments, but their use depends on specific operating conditions:

D400 and above: Inserts are always recommended – traffic loads (roads, wheel crossings) require maximum protection.
Lower classes (sidewalks, parking areas): Inserts are not always necessary, but they still provide advantages such as increased comfort and quieter operation.

Cheap Does Not Always Mean Cost-Effective: Purchase Cost vs. Maintenance Cost

Low-cost plastic solutions often promise the advantage of easy insert replacement. In reality, however, frequent replacements increase maintenance costs and are rarely desirable.

High-quality polyurethane inserts combined with well-designed geometry offer:

significantly longer service life
stable and quiet operation
lower total costs over time

Summary

Damping inserts are a key element in ensuring quiet and long-term reliable operation of manhole covers. Choosing the right material (ideally polyurethane) and a precise design solution – including accurate CNC machining of the contact surfaces – is essential to minimize problems and optimize overall costs.

For more information about damping inserts and other KASI products, feel free to contact us or read more blog articles on our web.