Dual-line lubrication system are normally used to provide measured quantities of grease to heavy duty plant and machinery. The installation can use smaller bore tubing to cover longer distances than is the case with single line systems.

Dual-Line lubrication system is composed of a central pump which supplies a series of metering distributors through two separate circuits: one of which acts as the lubrication supply line, while the second line is relieved of pressure via the line reversing valve. The purpose of this valve, which is situated between the pump and the distributors, is to direct the lubricant under pressure first to Line One then to Line Two, ensuring all points are served. The line reversing valve, which is also referred to as an inverter, can be mechanical, hydraulic or electrically operated.
Each piston in the metering distributor is adjustable for discharge stroke, and an indicator rod gives visual evidence of
correct volumes to each point. The hydraulic simplicity of a Dual-Line system, together with high operating pressures,
makes it very suitable for heavy duty applications.