Protecting the environment against pollution and contamination deriving from seepage of process fluids is known to be one of the most serious problems to solve, in that a perfect seal between parts undergoing axial or rotary movement is substantially very difficult to achieve, is generally very costly and is evidently more complicated the higher the pressure of the fluid to be contained.
In the field of pumps, compressors, turbines and rotary machines in general, this problem is currently solved by a seal system comprising an intermediate chamber formed between two separate series-arranged seal members and into which a neutral barrier fluid, generally nitrogen, is continuously injected at a pressure slightly higher than that of the process fluid, which is hence unable to leak whereas the neutral barrier fluid continuously discharges, to be collected and re-used after repressurization with a pump.
Although this solution ensures zero loss, it has a series of drawbacks such as the need to use a pump and a dynamic pressure regulator, which has to be more precise, and hence more costly, in keeping the pressure difference small the smaller the amount of auxiliary fluid allowed to leak into the process fluid, with evident constructional and plant complications and a considerable power consumption, resulting in an increased cost and overall size to an extent unacceptable for a simple process valve. A further drawback is that there is always a considerable flow of the neutral barrier fluid, with consequent considerable losses, hence making it impossible in practice to detect small anomalies in this flow and thus to warn of possible danger before irreparable damage occurs due to leakages of the process fluid itself.