How a Mechanical Seal Works

The figure provided here illustrates the basic operation of a mechanical seal. A mechanical seal consists of two main elements:

a. Rotating element

b. Stationary element

The primary sealing duty is carried out between the seal’s rotating and stationary elements. Whereas in the case of a compression packing the sealing action is provided by pressing of stationary packing elements against the rotating shaft. This is a key point to note. To repeat: primary sealing duty is carried out between the seal’s rotating and stationary elements. That means since pump's surfaces are not involved in the sealing operation - no wear and tear takes place on the pump's equipment.

The figure provided here illustrates a Single Internal Seal. The term “single” indicates only one sealing surface is provided, and the term “internal” indicates the sealing surface is inside the stuffing box. This type of design is very common in industrial applications.

Here’s a description of the key elements of a mechanical seal:

The pump shaft is indicated by “A” in the illustration.

The rotating element (“C”) is mounted on the shaft. It rotates along with the shaft. There is no relative movement between the rotating element and the shaft. An O-ring is usually installed between the rotating element and the shaft – this O-ring is indicated by “D” in the illustration. The interface between the O-ring and the shaft is referred to as the “Static Seal Point of Rotating Unit to Shaft”. The "O" ring and the rotating element are mounted on the pump shaft and rotate with it.