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What is the difference between a single mechanical seal and a double mechanical seal?

To start, let us define what a mechanical seal is: a mechanical seal is a specific part that seals an industrial machine together, specifically when connecting rotating parts with stationary parts. These integral little devices are crucial in assuring that there is no leakage between the outside environment and the interior of an industrial mixer. Mechanical seals come in two main types: single and double mechanical seals.

Each single mechanical seal consists of a spring holding together two surfaces, layered flat. These surfaces are designed to slide against each other and have a thin film between them to reduce the harmful friction that would otherwise ruin the mechanical seal. Additionally, this layer of fluid absorbs any excess heat created from this potential friction. It is important to keep in mind that a small amount of content will leak from the area of high pressure to the area of low pressure (into or out of the mixer) through a single mechanical seal and therefore this type of mechanical seal is most commonly used when the product being made will not have a harmful effect on the outside environment. Different kinds of single mechanical seals include rotary external seals, mixer split seals, and mixer mechanical seals.

What makes a double mechanical seal a double mechanical seal is simple, these seals consist of two of the single mechanical seals arranged together in one of two ways. With a double mechanical seal there is both a primary seal to contain the contents of the pump within and a secondary seal to ensure that no excess fluid leaks into the external atmosphere. A double mechanical seal can be arranged either back-to-back or face-to-face. For a back-to-back arrangement, two seal rings will face away from each other as they rotate. On the other hand, a face-to-face arrangement involves two seal rings connected on the spring side, with the sliding motion from the opposite direction to the stationary parts of the seal. A double mechanical seal is vital if the contents being processed are in any way hazardous to the external environment, because there is no risk of leakage. Kinds of double mechanical seals include high viscosity cartridge seals, mixer cartridge seals, and slow speed gas cartridge mechanical seals.

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