The Difference Between Single and Double Mechanical Seal

You might have heard about single and double seals and which one to use when. However, do you know the difference between the two? You need to understand the difference between the seals to select the one that’s more compatible with your system and processes. Here’s a list of differences between the seals and what effect they may have on the overall process.

Number of Seals

As the name implies, a single seal has one seal, whereas a double seal has two seals known as primary and secondary seals in a single component. A primary seal, also known as an inboard seal, performs the same functions as a single seal. A secondary seal is known as an outboard seal. An inboard seal helps to keep the fluid within the system, whereas an outboard seal prevents the buffer liquid from escaping.


As double seals have two seals in a single component, they’re more complex than a single seal.


A single seal has two faces, whereas a double seal has four faces.


Single mechanical seals use the fluids from the pump or the process for lubrication, whereas double seals have a separate buffer or barrier liquid.

Robco of America Double Cartridge Seal EV-07


While single mechanical seals are more commonly used, there are some specific conditions under which double mechanical seals are preferred. Following is when you should opt for a double mechanical seal:

  • If the fluid or the vapor of the fluids poses a threat to working conditions or the environment.
  • If the operational conditions include high pressures or temperatures.
  • If the medium is sticky.


While both double and single mechanical seals serve the same purpose and have similar benefits, double mechanical seals offer better sealing than single seals. This helps to:

  • Ensure complete sealing safety This is extremely important, especially when the process fluid is toxic.
  • Have full control of the system – As double seals offer zero-emission compliance, it helps to maintain the internal conditions of the system.
  • Protect the environment – It offers a level of safety that single seals can’t provide. With no leakage at all, single seals help to keep our environment protected.

If you’re looking to install single or double mechanical seals to your system, contact Robco of America. We’re a mechanical seals company that offers the best-engineered sealing solutions. Call 1-800-662-0585 for all kinds of mechanical seals and services.

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