In reciprocating compressors the compression chamber is sealed against the distance piece by means of a piston rod packing. 100% sealing efficiency is technical not possible even in case of piston rod packings with a buffer gas system there is a possibility that process gas is able to enter the first distance piece.
Therefore, when compressing flammable, explosive or toxic gases the compressor layout usually includes a double distance piece and the two distance pieces are separated by so-called intermediate packing. This avoids the formation of a dangerous gas mixtures. Intermediate packings can be classified into purge, non-purged and buffered versions.
The design of a STASSKOL intermediate packing is similar to the design of a piston rod packing. Leakage of lubrication oil into the distance piece is prevented by the use of suitable sealing elements. STASSKOL manufactures intermediate packing in several concepts.
The STASSKOL standard is a purged version. This packing consists of a basic case with two covers in a modular desing. An additional chamber ring can be installed between basic case and cover to mount a second leakage sealing, together with O-rings. serves for the sealing if intermediate packing. The standard intermediate packing also has a connection for purge gas and additionally a labyrinth ring with a thread groove at the inside diameter. Generally, nitrogen gas is used as a purge agent.
MODE OF OPERATION
In the standard intermediate packing the thread groove of the labyrinth ring is used to force the purge gas into rotation around the reciprocating piston rod. By doing so, no product gas can enter the second distance piece and therefore, not into the crak case.
Nitrogen is used as the purge gas. Due to design specifications the nitrogen flow is into the distance piece of the compressor. From there, it flows to the leakage gas pipe.
A change of both the wear parts as well as the complete intermediate packing is possible. In these case the connection between cross head and piston rod must be disconnected. It is vital to ensure that the piston rod thread is covered by a conical mounting sleeve in order to prevent damage to the internal parts.
The outside diameter of the mounting sleeve must not in any case exceed the nominal size of the piston rod.