What is a double seal?
A double mechanical seal, also called dual mechanical seal, is designed for the maximum sealing safety. Such kind of mechanical seals virtually get rid of leakage of the mediums in the pumps or mixers.
- Double seals provide a level of safety/zero emissions compliance not possible with single seals, which is essential when pumping or mixing a dangerous or toxic substance.
- Double seals are a must-have for some certain applications.
- Double seals are increasingly used to meet specific environmental goals or emissions requirements.
- A properly installed double seal also allows for nearly complete control over the seal operating environment and fluid film over the seal faces. This factor alone can greatly maximize seal life.
How double seals work?
Double mechanical seals have two sets of primary seals with a barrier or buffer fluid area in between. Each seal consists of a softer, narrower stationary face accompanied by a harder, wider rotating face. This arrangement enables the softer seal to wear while maintaining the integrity of the harder faced seal during service.
When to use double seals?
Pump and seal manufacturers recommend double seals for a variety of reasons such as:
- Prevent a hazardous product from reaching the atmosphere/polluting the environment;
- Avoid leakage of an expensive process fluid product;
- Maximize seal life by controlling the type of fluid film on the seal faces;
- Isolate the mechanical seal from atmospheric conditions;
- Provide an alternative when the process fluid will not provide stable and reliable lubrication of the seal faces (such as gaseous media, viscous fluids, non-settling slurries, or fluids liable to harden);
- Establish a backup seal in the event of an inboard seal failure or planned equipment repair (or to identify seal failure during operation);
- Avoid contamination of the process media should one seal fail.
Double Seal Configurations
Double mechanical seals come in rotary and stationary versions. There are three typical configurations:
- Back-to-Back: Typically used for general applications;
- Tandem (sometimes referred to as "Face-to-Back"): Provides absolute backup should one seal fail;
- Face-to-Face: Stationary – Becoming less popular.