How to determine the types of double mechanical seal

The types of double mechanical seal is mainly determined by the arrangement of its friction pairs (such as back-to-back, face-to-face, axial/radial) and whether the sealing chamber is under pressure, combined with the presence of an external sealing system for comprehensive identification.
Background
Determine the classification of dimensions and types of double mechanical seal
The following are several key dimensions for determining the types of double mechanical seal:

1. Classification of massage brush arrangement methods
This is the most crucial criterion for judgment, which directly affects the installation structure and performance characteristics.
Type, structural characteristics, sealing chamber, pressure state, typical application scenarios, source
Back to Back: Two moving rings face outward, with the stationary ring in the middle, forming a "dynamic static | static dynamic" structure. It is often a pressurized double seal, with the sealing liquid pressure higher than the medium pressure, and is widely used, such as in sulfur recovery units
Face to face arrangement of two moving rings, forming a "static dynamic | dynamic static" structure, can be used in situations where there is limited installation space for non pressure or low-pressure sealing systems
Tandem type with two sets of single end seals arranged in the same direction, non-contact layout is usually a pressure free double seal. After the first stage fails, the second stage can still work in high safety requirements scenarios, such as high-temperature methanol pumps
(Additional explanation) Back to back type is currently the most widely used form of double end mechanical seal, often referred to as "double end seal" in a narrow sense.

2. Classify types of double mechanical seal according to the pressure state of the sealed chamber
According to whether the sealing liquid is pressurized externally, it can be divided into two types:
Pressure double end face seal:
The externally introduced sealing pressure is higher than the medium pressure (generally 0.05-0.15MPa higher), which can effectively prevent medium leakage and improve lubrication conditions. Suitable for volatile and toxic media.
Non pressure double end face seal:
The pressure inside the sealed chamber is equal to or slightly lower than atmospheric pressure. When the main seal leaks, it can be detected by a liquid level or pressure rise alarm. The security is slightly lower but the system is simple.

3. Classify types of double mechanical seal  by structural direction
Axial double end face seal: Two pairs of sealing end faces are arranged in sequence along the axis direction, with a compact structure.
Radial double end face seal: The sealing end faces are distributed in a circular shape in the radial direction, occupying little axial space and suitable for situations where axial dimensions are limited.

4. Whether to use modular design
Modern double end mechanical seals often adopt a modular structure, which pre installs all components into one unit for easy installation and ensuring assembly quality. It can be determined whether it is a container type by observing whether there are positioning pieces, overall card boards, and other structures.

suggestion
To accurately determine the type of double-sided mechanical seal used in a device, it is recommended to:
View equipment technical information or sealing model manual;
Observe the physical structure (such as disassembly diagrams or photos) to determine whether it is back-to-back or face-to-face;
Check for the presence of external sealing tanks, pressure regulating devices, and alarm systems to determine whether there is a pressure or non pressure system;
If unsure, contact the manufacturer to provide a sealing layout diagram for confirmation.