Mechanical seal
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Why does a dry gas seal have a higher leakage rate than a regular mechanical seal?
The moving ring end face of the dry gas seal features gas grooves, whose depth is only a few micrometers. Clean gas must be present between the end faces to ensure the formation of a stable gas film that keeps the sealing end faces fully separated. The thickness of the gas film is generally a few micrometers. This stable gas film helps maintain a certain sealing gap between the sealed surfaces; if the gap is too large, the sealing effect deteriorates ； If the gap is too small, the sealing surfaces will come into contact; since the frictional heat generated by the dry gas seal cannot be dissipated, the lack of lubricated contact between the end surfaces will quickly cause deformation of those sealing surfaces, thereby leading to seal failure.
The liquid-sealed surface develops surface tension, which functions like a sealing film and serves to provide sealing as well as cooling effects. Therefore, dry types do not form a sealing surface, which can result in some leakage.
I am a process engineer, and I have a question regarding mechanical seals. It is known that double-end face mechanical seals used in centrifugal pumps have different requirements regarding the pressure of the sealing water. However, the chief engineer of a pump manufacturer said that their double-end face mechanical seals do not require any specific pressure for the sealing water; as long as the temperature is not too high and the water is in motion, it is sufficient. The spring inside the mechanical seal helps maintain the balance between the moving ring and the stationary ring. Could someone please help confirm whether this type of mechanical seal exists? Thank you.
Pressure difference requirements are specified in the selection manuals for mechanical seals
There is some truth to this; the sealing water primarily serves a cooling and flushing purpose. As a key component of double-end face seals, the adjustment springs found in the moving ring seat can be either double-acting or single-acting. Single-acting springs do not require any specific water pressure, while double-acting springs theoretically need water pressure to balance the spring force – but in practice this is not the case, as the seal chamber already determines the extent to which the spring can expand or contract. OK! I have the chance to discuss things related to the machinery sector.
For dry gas seals: a certain amount of leakage serves to cool and lubricate the sealing ring, which facilitates the formation of an air film and helps to separate the components within the sealing gap.