Piston rod gas packings perform the critical function of containing gas in the compression end of a compressor. The two most widely used gas packing design styles are Chevron and Tangent-Tangent. There are pros and cons to both designs. However, Hycomp employs the Tangent-Tangent packing style due to quality and efficiency. The following article will explain why.
Chevron Gas Packings (V-Packings):
Chevron gas packings are also referred to as V-Packings or Vee-Packings due to their shape when viewing them as a cross-section. The chevron packing arrangement is a combination of three main sections: the Base Seal (bottom), the “V-Rings” at the center and the Pressure Ring (Top). The V-Rings provide the main seal that while the base seal supports the center rings from getting extruded during high pressure applications and the Pressure Ring helps hold it all together while providing a method of adjustment. Pressure is applied to the V-Packings by both the Pressure Ring and the Base Seal, causing the V-Packings inside to widen or squish and provide the seal (see illustration). As the packings wear, the seals loosen and the Base Seal and Pressure Ring must then be re-tightened.
The main problem of this design is the constant adjustment necessary to keep a tight working seal as the packings wear. Depending on the intervals of use, the need for re-adjustment can occur frequently. Monitoring the performance of the compressor combined with the constant need for adjustment leads to higher costs and decreased efficiency in the long run.
Tangent-Tangent Gas Packings:
Tangent-Tangent Gas Packings (TT Packings) provide a dynamic seal that does not require constant monitoring and continuous tightening. This packing style is self-adjusting and therefore provides a tighter and more efficient seal throughout the entire life of the packing.
Tangentially cut, this segmented packing design provides a dynamic seal by lining up and sandwiching each set of packings via a white pin for alignment at the proper rotational offset to ensure that the leakpath created by the cuts is minimized (see illustration). The Tangent-Tangent (TT) style packing inherently continues to seal as the packing wears due to the tangentially cut design, dynamic pressure and a small spring that helps hold the pieces together inside the packing gland.
TT Packing arrangements can be configured to provide even more stringent containment by increasing the amount of packing pairs, incorporating purge/vent lines or by utilizing an additional plenum chamber filled with a pad gas. Hycomp compressors can be designed and engineered using all three methods of containment when gases are either very dangerous or contain very small molecules, or both.
When increased gas containment is necessary another set of gas packings is added and purging gas lines are used to carry away any gas that has entered the purge chamber between the bottom two sets of gas packings (see illustration). For applications that require extreme containment, purge lines are employed along with an additional plenum chamber. The second plenum chamber is pressurized with an inert pad gas to provide opposing force and to ensure process gas purity (see illustration).
The end result of using Tangent-Tangent Gas Packings is a reliable and consistent seal. Chevron gas packings are less expensive as an initial purchase, but require continuous monitoring and constant re-adjustment, which leads to an overall higher cost and increased hassle. Tangent-Tangent packings are far more user-friendly as they are self-adjusting and do not require constant monitoring or maintenance.