Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/825468
36 | May - June 2017 | www.machinerylubrication.com AUTOMATIC LUBRICATION from line 2 forces the pilot piston to the right, allowing pressure to be applied to the left side of the main piston, which begins to move to the right. In the same manner as above, the main piston forces the lubricant on the right side to pass the pilot piston and the check valve, and then reach the bearing via the outlet. The illustration above shows one version of a dispenser design used for both oil and grease. When pressurized, the plunger forces the lubri- cant in the measuring chamber out to the bearing. In the upper position, the measuring chamber loads with a preset volume. Single-line Volumetric Systems Single-line volumetric systems require only one header line. They are generally used for oil lubrication, but there are some models specifically designed for grease. Like dual-line systems, single-line volumetric systems are simple to maintain and under- stand, and the number of points can be easily expanded or reduced. In these systems, the dispenser must reload after a lubricating cycle. This means the piston in the dispenser must overcome the lubricant pressure in the pump line. The models designed for grease are equipped with strong springs that allow reloading of the dispenser at relatively high venting pressures. Single-line Progressive Systems The heart of a single-line progressive system is the progressive divider. It has at least three dispensing elements, each with a hydraulically driven spool that feeds a fixed amount of grease during the stroke from one end to the other. The volume is defined by the diameter and length of the piston stroke, which cannot be adjusted. The spools are internally connected through a cross-porting arrangement that forces them to work in sequence, one after the other. If one spool is not able to fulfill its stroke, the divider will stop working. These systems are often designed with one primary divider and a number of secondary dividers. Monitoring one spool in any of the dividers will give full control of the whole system, provided there is no leakage in the tubing from the divider to the wear surface. Single-line progressive systems offer flex- ibility and can be used alone or in conjunction with other systems, such as direct-feed, dual-line and manual systems. They can handle both oil and grease, and are less expensive than dual-line systems. However, these are large systems with several secondary dispensers, so they can be more difficult to maintain and understand. Single-point Systems The first automatic single-point lubrica- tors consisted of a spring-loaded piston that was charged with grease. The spring extruded the grease through an orifice, with flow dependent on the orifice, the spring force and the stiffness of the grease. These factors limited the spring-activated models, which have had only a limited impact on the market. Single-point Lubricators During the last 20 years, new single- point lubricators (SPLs) have been introduced and have increased in popu- larity. The latest SPLs are easy to install and do not require a significant financial invest- An example of a dual-line system A dual-line system with a dispenser designed for both oil and grease Line 1 Line 2 Feed Line to Bearing Measuring Chamber Plunger Plunger Indicator Stem Outlet Check Valve Supply Line From Pump Supply Line From Pump Measuring Chamber Feed Line to Bearing VENT STAGE PRESSURE STAGE Line 1 Line 2 The vent and pressure stages of a single-line volumetric system