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Pressureless double mechanical seal and pressure double mechanical seal
- May 29, 2018 -

    Single-end mechanical seal is only a pair of friction pair, the structure is simple, easy to manufacture, dismantle, generally only need to set the flushing system, no external sealing system.

    Pressure double mechanical seal (formerly known as double-end mechanical seal) refers to two pairs of friction pairs. The structure is complex and needs to be used to seal the liquid system. Pressured dual mechanical seals in the sealed chamber are inserted at a pressure higher than the medium pressure by 0.5~1.5 bar. The spacer fluid acts as a sealer, lubricates, etc. The spacer fluid acts as a lubricant for the inner seal. Non-pressure double seal (formerly known as series seal) means that there are two pairs of friction pairs. The structure is complex and needs to be used to seal the liquid system. The buffer in the double-pressure sealed sealed chamber is not pressurized, and the process medium lubricates the inner seal. effect.

   Under normal circumstances, single-end mechanical seals should be preferred because single-end mechanical seals are simple, easy to use, and inexpensive. However, double mechanical seals are preferred in the following situations.

    (1) Poisonous and dangerous media.
    (2) High concentration of H2S.
    (3) Volatile, low-temperature media (such as liquefied petroleum gas, etc.).

    With the increasing emphasis on health, safety and environmental protection in society, the use of non-pressure double mechanical seals has increased year by year. The non-pressure double mechanical seals can be widely used for vinyl chloride, carbon monoxide, light hydrocarbons and other toxic, volatile , dangerous media. The inside seal (first seal) of the pressureless double mechanical seal is the main seal, which is equivalent to a single end face built-in mechanical seal. The lubrication of the single end mechanical seal is performed by the sealed medium. The liquid filled in the sealing chamber to the sealing liquid tank is not pressurized. Non-pressure double mechanical seal Once the inner seal fails, the pressure in the seal chamber increases, which can be displayed, recorded or alarmed by the pressure gauge of the seal fluid tank. At the same time, the non-pressure double mechanical seal outside seal can play the role of sealing and containing leakage liquid before repair.

    For some toxic, particulate media (or corrosive media), the following methods can generally be considered:

    (1) Use appropriate environmental controls, such as external flushing + pipe flushing systems with cyclones.
    (2) Use a pressurized dual mechanical seal.

    The pressure of the pressurized dual mechanical seal spacer fluid is higher than the pressure of the medium so that the pumped medium does not enter the seal chamber. The pressurized double mechanical seal inside seal serves to prevent the spacer fluid from entering the pump chamber. Therefore, when transporting viscous, abrasive and high temperature media, the pressurized double mechanical seal inside seal can be made without expensive alloys because it is not exposed to the media. The pressurized double mechanical seal outer seal serves only to prevent leakage of the spacer fluid into the atmosphere.