EuroIndustriel

single-vs-double-mechanical-seal

Single Mechanical Seal Vs Double Mechanical Seal – What's the difference?

If you’ve recently started using mechanical seals, then you would probably be aware of the huge benefits for your industrial machinery and other systems. One of the main advantages of using mechanical seals is that they reduce leakage drastically, helping to save time and money in the long-run. Reduced leakage also leads to an increase in the lifespan of your mechanical systems.

What are mechanical seals? The Definition

what-are-mechanical-seals

Mechanical seals are components of a machinery. They create an air-tight seal between the rotating parts (like the shaft) and the non-rotating parts (like the pump housing). You can find mechanical seal in a variety of industrial systems. They are a key component of pumping systems.
The main role of a mechanical seal is to prevent the pumped fluid from leaking into the environment. They are available in two types: single mechanical seals and double mechanical seals. What’s the difference between the two? Are they the same? Which one is better? Continue reading to find the answer.

What is a single mechanical seal?

A single mechanical seal has two flat surfaces that are pressed together. These two surfaces slide and spring against each other. Between the two flat surfaces is a thin fluid film that is generated by the pumped fluid. This film prevents the mechanical seal from connecting with the stationary ring in the pump.
Without this fluid layer, the pump dry runs resulting in the generation of friction, which in turn, creates heat damaging the mechanical seal. Mechanical seals leak vapour when the fluid flows from the high-pressure end to the low-pressure end. The fluid that flows between the seal’s surface absorbs the heat generated and reduces friction.

When to use single mechanical seals?

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If the pumped fluid doesn’t pose any harm to the environment, i.e., if it’s non-hazardous, then single mechanical seals are adequate. They get the job done without causing any damages.

What is a double mechanical seal?

A double mechanical seal contains two single mechanical seals arranged serially. The primary seal (also known as the inboard) keeps the pumped product housed within the pump housing. The secondary seal (also known as the outboard) prevents any flush liquid from escaping into the environment.

Double mechanical seals are usually arranged in two configurations:

Back-to-back

Here, two rotating seal rings face away from each other. The barrier fluid generates the layer of lubricating film. Back-to-back seals are primarily used in pumps in the chemical industry. If there is any leakage, the barrier liquid enters the product.

Face-to-face

In this configuration, there are two spring-loaded rotary seals that face each other. They slide in the direction opposite to the stationary seal parts. Face-to-face configuration is mostly used in the food products, specifically for pumping foods that tend to stick. If there is any leakage, the barrier liquid enters the product. If the pumped fluid is hot, the barrier liquid absorbs the heat and acts as a cooling agent.

When to use double mechanical seals? Double mechanical seals are generally used in the following scenarios:

  • When the fluid and its vapours are harmful to the environment and must be contained within the system
  • When the pumped fluid is sticky and polymerising
  • When the pumped fluid is corrosive and is transported at high temperatures or pressures

In this configuration, there are two spring-loaded rotary seals that face each other. They slide in the direction opposite to the stationary seal parts. Face-to-face configuration is mostly used in the food products, specifically for pumping foods that tend to stick. If there is any leakage, the barrier liquid enters the product. If the pumped fluid is hot, the barrier liquid absorbs the heat and acts as a cooling agent.

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