Mechanical seal. Double mechanical seal: GOST

The mechanical seal is a unit used for sealing in parts of the pump where the shaft passes through the cover. A sufficient density is formed by a strong pressing on the surfaces of two elements - rotating and stationary. The parts must have high accuracy, it is achieved by grinding and grinding.

Mechanical seals for dry-type pumps prevent liquid from entering the environment, and in submersible pumps, do not allow water to flow into the engine, avoiding the occurrence of a short circuit. To increase the accuracy on one shaft, there are two seals using a dielectric (oil or cooling mass).

The sealed unit can be balanced, have a cartridge or collapsible structure. The fluid pressure, its type and temperature affect the hard or soft materials used. Extensive distribution acquired alumina, graphite with impregnation, carbide. As a secondary seal, the use of rubber is possible.

How to extend the service life

It should be noted that such elements are subject to rapid wear and are sensitive to the environment, but despite this, are the most accurate. Most of the difficulties in the operation of pumps are associated with the breakdown of the device. The service life is reduced due to many reasons, for example, due to the impact of abrasive particles or elevated temperatures. It is also affected by improper use. To ensure that the mechanical seal lasts longer, it is important to choose the composition that corresponds to the tasks.

Emulsions and oils are not suitable for rubber, as it is not resistant to refinery products. In this case, Viton is used for compaction. Dry running, which contributes to overheating, can lead to damage to the device. Systematic air release through the installed pump outlets is required.

A special value is the competent adjustment of automation. Also there is a possibility of sticking, in which the planes are glued together after idle time or the rubber is soldered to the shaft. To prevent blocking, it is sometimes necessary to scroll the shaft.

Double seal

The type, material and construction of the seal depend on the conditions in which the work and features of the pumped liquids take place. A single seal is used for liquids that are not explosive and fire hazardous, as well as for explosive substances of categories T1, T2 and T3.

Double seal is used for liquids that do not fit single. These are environmentally hazardous compounds, toxic, corrosive or abrasive substances. It is worth noting that under difficult operating conditions, this design serves five times longer than others. In addition, its inner metal part is resistant to environmental influences, and thermoset, viscous masses are quickly sealed without additional costs.

In accordance with GOST R 52743-2007, a double mechanical seal is used for explosive liquids of category T4. The emission standards for damage, the period of use and the cost of double sealing allow for the final choice.

Among the general requirements for mechanical seals is the compatibility with the landing and overall dimensions of the pumps. The general structure should provide for the previous operating mode with a low mass pressure in the tank in comparison with the medium to be sealed. The use of a double seal eliminates the possibility of leakage. The material for the body elements must fully comply with the technological characteristics of the transferred liquids.

Gas barrier

It resembles a double seal cartridge, while the inert gas is used as a cooling and lubricant, as well as instead of washing with a water jet or cooling liquids. Such a system was developed in view of the fact that some of the barrier formulations used earlier can not be used because of the discrepancy with the updated emission standards.

Seals in the role of a gas barrier use harmless air or nitrogen, which allows to prevent substances from entering the environment and meet established emission standards. In situations requiring increased reliability, or when transporting hazardous or toxic formulations, structures with a gas double barrier should be used.

By the way, the average price (mechanical seal with a gas barrier) is about 2 thousand rubles.

Tandem

Environmental and health standards regulate the use of a tandem for the transfer of substances such as hydrocarbons, carbon monoxide, vinyl chloride and an extensive list of other carcinogenic or volatile compounds.

Such a device makes it possible to prevent icing of light hydrocarbons and liquids that are characterized by a drop in temperature below the freezing point of water. Propanol and methanol are typical examples of formulations having buffer characteristics. Also, the tandem increases the degree of reliability. When a conventional design breaks down, the external component takes over the maintenance tasks.

Without a spinner

To support the contact of the sealing planes, it is undesirable to move the structure along the sleeve or shaft. Among the main advantages it is worth highlighting the operability with a wide temperature range and the absence of the need for an additional seal.

Negative moment is the modernization of cross-sections when used in harsh operating conditions.

Stalker

To ensure contact of the surfaces of the units, it is required to connect a secondary mechanical seal, which is moved along the axis of the sleeve or shaft. Due to this property, damages are compensated in the front plane of the device. Its advantages include a fairly low cost and an extensive range of pushers, presented in stores in various configurations and sizes. But it should be noted that it can lead to corrosion damage to the bushing and to the movement of the secondary seal.

Balanced devices

The balancing of the seal includes a simple transformation of the structure, which reduces the hydraulic force that closes the shaft seal. Balanced nodes are distinguished by the release of less heat, a small load of sealing planes and an increased pressure. Due to this, they become the best option for transferring compositions with high vapor pressure and lubricating inadequate capacity.

Unbalanced elements

They have great stability when changing cavitation and alignment, with a small number of leaks and low cost. A sufficiently low pressure level is a disadvantage of such structures. If the set pressure limit of the resultant reinforcement acting on the sealing parts is exceeded, the film located between the surfaces is squeezed out and the work gets dry.

Standard

As an example, Grundfos - mechanical seals, which require mounting and alignment on a bushing or shaft. Despite the simple method of installing the device, maintenance costs are now in priority, which leads to a greater distribution of cartridge designs.

Internal single

Wilo mechanical seal of this type is the most popular. There is the possibility of an easy change for the formation of a buffer system for washing, balancing for transferring increased pressure to the environment. It is recommended for use for aggressive and non-aggressive liquids with lubricating sufficient characteristics.

Cartridge

This category includes end seals for pumps installed on the hub, including the shaft sleeve and the gland cover, which has a close fit to the shaft. Their main advantage lies in the fact that there is no need to use connecting elements for their installation. Due to such designs, the probability of errors during installation is reduced and operating costs are reduced .

External single

Such a mechanical seal becomes a budget alternative alternative to expensive metals that are needed to give corrosion resistance to internal seals, provided that there are high lubricating characteristics of the aggressive fluid. True, it is worth noting among the disadvantages of susceptibility to hydraulic pressure and the impact of shocks, which is why the seals of this type have low pressure limits.