Compression packings used in pumps, whether in rotating or reciprocating service, normally depend on a fluid film between the surface of the moving member of the equipment and the packing for lubrication. Sources of this fluid film are built-in lubricant supply.
On equipment start-up, lubricants may be released from the packings by gland pressure to provide initial lubrication and sealing. During the break-in period, these lubricants bridge the period between dry operation and the introduction of the normal lubricating system. Gradually, by adjustment of the gland pressure, the pumped medium or the external lubricating source, takes over the lubricating function by providing a continuous source of fluid film. Gland pressure is regulated to provide optimum lubrication to seal and prevent overheating and consequent damage to the shaft or rod. Built-in lubricants that are lost gradually during the operation of the equipment are compensated for by further gland adjustment. When the volume loss of lubricated packing approximates the original amount of built-in lubricant , the effectiveness of the packing is lost and replacement is required. Built-in lubricants may also serve the important function of blocking the passage of the medium being pumped through the packing rings. Compression packings used in valves where there is slow or infrequent motion and those used in static operations are required to seal without leakage. Various impregnants ma be used to assist in this function. Some packings are designed with non migrating stable lubricants for operation under extreme pressure and temperature.
Depicted below are typical methods of the use of compression packings in pumps. Note the use of lantern rings (seal cages) where external means of lubrication are required.