Mechanical Seal Classification by Arrangement

Mechanical seals are critical components used to contain fluid within rotating equipment such as pumps, compressors, and mixers, where a rotating shaft passes through a stationary housing.

Primary Functions of Mechanical Seals:

1. Fluid Containment – Preventing process fluid or gas from leaking out of the equipment.

2. Pressure Maintenance – Ensuring the operational pressure within the system is maintained.

Classification of Mechanical Seals:

Mechanical seals can be classified in three broad categories:

• By Arrangement (Focus of this article)

• By Design

• By Configuration

According to API 682 (4th Edition), mechanical seals are categorized based on arrangement as follows:

Arrangement 1: Single Seal

Arrangement 1 refers to single seals, which consist of a single pair of seal faces (seal ring & mating ring) that prevent fluid leakage from the seal chamber. This configuration is most suitable for applications where the process fluid is non-toxic, non-flammable, and relatively inexpensive.

Key Characteristics:

• Cost-effective solution.

• Simpler piping plans requiring minimal monitoring.

• Easier maintenance compared to dual-seal arrangements.

Leak-Proof Engineering's Solutions: Leak-Proof Engineering offers a range of Arrangement 1 mechanical seals, such as LPA 90S, LPA 45S, and LPA 47S, which are API 682-qualified and have successfully sealed pumps worldwide.

Before discussing Arrangements 2 and 3, it's important to understand the distinction between buffer fluid and barrier fluid in dual mechanical seals.

Buffer vs. Barrier Fluid:

In dual mechanical seals, two sets of seals are used:

• Inboard Seal – The seal in contact with the process fluid.

• Outboard Seal – The seal on the atmospheric side.

• The cavity between these seals is filled with an external fluid, which can be either a buffer or barrier fluid:

  • If the external fluid pressure is lower than the process fluid pressure, it is called buffer fluid.

  • If the external fluid pressure is higher than the process fluid pressure, it is called barrier fluid.

Arrangement 2: Dual Seal with Buffer Fluid

Arrangement 2 consists of dual seals arranged in series, commonly referred to as tandem seals. In this configuration, the cavity between the seals is filled with buffer fluid, which operates at a lower pressure than the process fluid.

Key Characteristics:

• Designed for applications involving toxic, flammable, or hazardous fluids.

• Outboard seal leakage consists of a mixture of process fluid and buffer fluid.

• More complex piping plans requiring regular supervision.

Leak-Proof Engineering's Solutions: Our LPA 90T and LPA 45T mechanical seals are designed to reduce emissions and enhance plant and personnel safety in hazardous environments.

Arrangement 3: Dual Seal with Barrier Fluid

Arrangement 3 seals are dual-seal configurations where the inboard and outboard seals both operate on an externally supplied barrier fluid, ensuring zero leakage of process fluid into the environment.

Key Characteristics:

• Used in applications where product contamination must be avoided.

• Essential for handling highly toxic or flammable process fluids.

• Requires sophisticated piping plans and continuous monitoring.

Leak-Proof Engineering's Solutions: Our LPA 90B, LPA 90F, and LPA 47F mechanical seals have demonstrated exceptional performance under extreme conditions.

Conclusion:

• Arrangement 1 is the most economical and easiest to maintain but is unsuitable for handling toxic or flammable fluids.

• Arrangement 2 & 3 are more complex and costlier but provide enhanced safety and reliability in hazardous applications.