Торцевое механическое уплотнение: конструкция и применение.

Seal made by two rotating parts pressed together at their end faces

In mechanical engineering, an end face mechanical seal (often shortened to mechanical seal) is a type of seal used in rotating equipment, such as pumps, mixers, blowers, and compressors. When a pump operates, the liquid could leak out of the pump between the rotating shaft and the stationary pump casing. Since the shaft rotates, preventing this leakage can be difficult. Earlier pump models used mechanical packing (otherwise known as gland packing) to seal the shaft. Since World War II, mechanical seals have replaced packing in many applications. An end face mechanical seal uses both rigid and flexible elements that maintain contact at a sealing interface and slide on each other, allowing a rotating element to pass through a sealed case. The elements are both hydraulically and mechanically loaded with a spring or other device to maintain contact. For similar designs using flexible elements, see radial shaft seal (or "lip seal") and O ring.

An end face mechanical seal consists of rotating and stationary components which are tightly pressed together using both mechanical and hydraulic forces. Even though these components are tightly pressed together, a small amount of leakage occurs through a clearance that is related to the surface roughness.

By definition, the seal ring is the axially flexible member of the end face mechanical seal. The design of the seal ring must allow for minimizing distortion and maximizing heat transfer while considering the secondary sealing element, drive mechanism, spring and ease of assembly. Many seal rings contain the seal face diameters, although this is not a requirement of the primary ring. The seal ring always contains the balance diameter. The shape of the seal ring may vary considerably according to the incorporation of various design features. In fact, the shape of the seal ring is often the most distinct identifying characteristic of a seal.

The individual components of end face mechanical seals may be designed to include features such as: When the components are pre assembled onto a sleeve and gland plate, the complete assembly is called a cartridge seal. This complete assembly can be easily slid onto the shaft and bolted in place thus reducing the potential for installation errors. Some cartridge seals use regular component seal parts whereas other cartridge seals might use specific purpose parts. API 682 specifies that only cartridge seals are acceptable to the standard.

Either the seal ring or the mating ring may be the rotating element. Seals with rotating seal rings are said to be "rotating" seals; seals with stationary seal rings are said to be "stationary" seals. Because the springs are always associated with the seal rings, sometimes the distinction is made as "rotating springs" versus "stationary springs". For convenience, rotating seals are used in most equipment; however, stationary seals have some advantages over rotating seals. In small, mass produced seals for modest services, the entire seal may be placed in a package which minimizes shaft and housing requirements for the equipment. Stationary seals are also used to advantage in large sizes or at high rotational speeds.

When classifying end face mechanical seals by configuration, the first consideration is whether there is only one set of sealing faces or multiple sets. If multiple sets are used, are the sets configured to be unpressurized or pressurized.

A tandem seal consists of two sets primary sealing surfaces with the space in between the two seals filled with a compatible low pressure fluid called the buffer fluid. This buffer fluid/space may be monitored to detect performance of the assembly. Unfortunately, the definition of “tandem seal” was often stated in a confusing manner. In particular, a tandem seal was usually described as two seals pointing in the same direction; that is, in a face to back orientation. This orientation is not necessary to the function of the configuration and the API chose to use the term Arrangement 2 instead of tandem in the API 682 standard.

A double seal consists of two sets primary sealing surfaces with the space in between the two seals filled with a compatible pressurized fluid called the barrier fluid. This barrier fluid/space may be monitored to detect performance of the assembly. Unfortunately, the definition of “double seal” was often stated in a confusing manner. In particular, a double seal was usually described as two seals pointing in the opposite direction; that is, in a back to back orientation. This orientation is not necessary to the function of the configuration and the API chose to use the term Arrangement 3 instead of double in the API 682 standard.