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"Should you avoid installing pipe extensions in relief ports? We have been told this practice can increase the resistance path to obtain a purge."
It is true that the installation of an extension line will produce a longer path for grease to purge out of a bearing, creating more of an opportunity for grease to clog in the purge line. However, this may not be a significant issue if the grease being expelled maintains its original consistency. The real concern is whether the grease is caking and becoming harder.
Grease hardening can be caused by several different factors, including the presence of external contaminants like solid particles or moisture. It may also be the result of high temperatures. This can lead to oil bleeding from the grease or eventually oil evaporation. Using a poor-quality grease or mixing two different products can produce a similar effect. Overextended regreasing intervals may contribute to this problem as well.
When grease hardening takes place, it often occurs in the fill port line, drain line or bearing cavity. If you are experiencing this type of issue, the use of extension lines may worsen the situation. The source of the grease hardening should be identified to correct or mitigate the problem.
In addition, you should take into account the reason why an extension line is being considered for the purge port. These lines typically are installed to expel and discard old grease in a location where they may be cleaned or inspected easily and safely. If inspection and cleaning of the lines may be performed safely and easily without using extensions, it generally would be better not to install them. Instead, try utilizing just the purge valve along with a grease fitting and a valve relief.
If you choose to install extension lines, it is recommended to disassemble them periodically to ensure they are not blocked with hardened grease. This practice should be implemented even if the grease is not showing any issues related to hardening or caking. Also, keep in mind that slightly overlubricating the component to expel extra grease in good condition may improve grease flow.
Finally, a general rule to remember is that when you retrofit machines with modifications to help lubricate the equipment or simplify the lubrication routines, it will be important to include inspections to verify that those modifications are working well.