Directly buried compensator can be divided into internal pressure type and external pressure type according to the different internal and external forces. The two types of compensators are significantly different in design, working principle, and application scenario. The following are the main differences between internal pressure and external pressure directly buried compensators:
Source of stress
Internal pressure compensator: The pressure mainly comes from the medium inside the pipeline, such as water, steam, etc. In this compensator, the medium flows inside the bellows.
External pressure compensator: Pressures outside the pipe, such as soil pressure or groundwater pressure, must be considered in addition to the medium pressure inside the pipe. In this type of compensator, the medium may be located outside the bellows, and the inside of the bellows may be air or another non-working medium.
Working Principle of Bellows
Internal pressure compensator: The bellows absorbs the thermal expansion of the pipe by compression. This is because internal pressure can cause the bellows to attempt to expand, but the constraints of the guide and the pipe make it compress, which absorbs axial displacement.
External pressure compensator: The bellows absorbs the thermal expansion of the pipe by stretching. External pressure, such as soil pressure, coupled with internal pressure allows the bellows to stretch upon thermal expansion, thus absorbing the displacement of the pipe.
Visibility and maintenance
Internal pressure compensator: In some designs, the internal pressure compensator can be cut in order to observe the condition of the bellows, which is helpful for maintenance and inspection.
External pressure compensator: It is usually not possible to cut through for inspection because if the working steel pipe is open, it can cause media leakage, which limits direct inspection of the bellows condition.
Pre-treatment before installation
Internal pressure compensator: Pre-stretching according to ambient temperature may be required prior to installation to ensure that the compensator responds correctly to the thermal expansion of the pipe.
External pressure compensator: Pre-compression according to ambient temperature may be required prior to installation to ensure that the compensator is properly stretched during thermal expansion of the pipe.
Cost
Internal pressure compensator: In general, the cost of internal pressure compensators is lower.
External pressure compensator: External pressure compensators are usually more expensive because of their more complex design.
Structural differences
Internal pressure compensator: The construction is relatively simple, the bellows are in direct contact with the medium and usually do not require additional protective layers.
External pressure compensator: More complex structures may be required to resist external pressure, such as requiring an outer protective tube or a reinforced bellows design.
Applicable scenarios
Internal pressure compensator: Suitable for most conventional heating and fluid delivery pipes.
External pressure compensator: It is more suitable for situations where external environmental pressures need to be considered, such as deep buried pipelines, crossing waters or areas with special geological conditions.
When selecting a directly buried compensator, the internal pressure or external pressure compensator should be decided according to the specific pipeline conditions, media properties, environmental factors and budget. The right choice ensures the long-term stability and safety of your plumbing system.