Carbon dioxide (CO₂) – a colorless gas (under normal conditions), easily soluble in water.

In addition to the widely known fact that it is an important element of the photosynthesis process, this substance is widely used in the food, pharmaceutical, agricultural, and mechanical engineering industries, among others.

In the technological process of carbon dioxide production, transportation means are essential, namely a pump unit. Carbon dioxide is in a liquid state at low temperature and high pressure.

In the photo below – a vertical multistage pump installed in the carbon dioxide production line. Frost (frozen water vapor contained in the air) is observed on the pump surface and shut-off valve.

The feature of this type of pumps is the ability to generate high pressure due to the number of impellers located on a single shaft one after another. This design allows achieving significant pressures (from 3 to 25 bar).

The disadvantage of vertical configuration is the danger of forming steam-air "plugs" in the upper part of the pump due to high liquid velocity and, consequently, local boiling of carbon dioxide.

It is in this part of the pump that the mechanical seal is located. This element prevents liquid leakage from the working chamber and should be cooled by the pumped liquid, but since a steam-air zone is formed where the seal operates without liquid – "dry running", the service life of the mechanical seal is significantly reduced.

In the case of "dry running", rapid wear of friction pairs and melting of rubber rings occurs.

To eliminate this problem, a bypass tube can be used. This pump piping element allows directing vapors to the suction line, thereby preventing the formation of a steam-air "pocket" in the mechanical seal area.