Using graphite insert materials to improve pump performance
The use of graphite, graphite-impregnated, or graphite-filled insert materials has gained wide acceptance as an option in improving pump performance in both original equipment and after-market upgrades.
These graphite-based materials, are considered to be "self-lubricating" to the extent that they can survive momentary upset conditions where loss of lubrication occurs between wear parts without seizing, such as when a pump unexpectedly stops running.
This property makes them ideal as "inserts" in case wear rings, throttle bushings, and other non-rotating wear parts, to reduce the running clearances between the mating parts. The reduced clearances, some as much as 50% of the standard clearances, can result in significant improvement in pump performance:
reduced clearances can minimize the leakage across the mating parts, which in turn will result higher efficiency; typical improvement is about 2 to 3 points depending on pump type and size
reduced leakage can help slightly increase the discharge head at the same discharge flow rate
reduced clearance can help dampen the pump vibration
graphite, and graphite-impregnated materials, are ideal in applications handling low specific gravity liquids that are considered to have poor lubricating properties, such as butane, propane, liquid carbon dioxide, etc.
There are many commercially available graphite, graphite-impregnated, or graphite-filled materials. Among the commercial trade names are graphalloy, peek, pure carbon etc. Consult their respective manufacturers for application recommendations. Some of these materials may not be suitable in abrasive, high temperature, or high-stress application.