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The art of lubricant application has evolved considerably since their invention. Early grease products, probably made from animal fat and lime, were likely applied by hand - to the maximum extent possible - and undoubtedly left much to be desired. There are still some applications where applying a lubricant by hand might still be relevant. But to a large degree, the task of relubricating components is highly repetitive, offers low value for personnel and can generally be cost-effective with a variety of automatic and semiautomatic lubrication systems.
System requirements may range from a simple, battery-powered, single-port, timed lubricator to a sophisticated dual-line reversing system with timers and alarms, covering thousands of points over hundreds to thousands of feet. Fortunately, there are systems designed for almost any application that may be divided into the following types:
This article does not discuss series progressive zone, air mist, air/oil or die spray systems. While these systems are important, they are somewhat application-driven, and require more information than space allows.
Single-Line Resistance System
SLRs, also referred to as orifice systems, are commonly found on small machines such as drills, small grinders, lathes, etc. Power is supplied via a manual hand pump or a small electric gear motor and pump (Figure 1).
Figure 1. Pump Package
SLRs are parallel in design. This means that each metering unit receives lubricant from a common header, and is parallel to each other. SLRs are for low-pressure oil applications with pressures ranging from 100 to 250 psi. These systems can be designed to run manually, intermittently with a timer or continuously. The metering devices can be mounted in a manifold with outputs to each component, or mounted immediately at each component.
Figure 2. Orifice Units
There are two styles of metering devices (Figure 2): a metering unit used in intermittent flow and a control unit for continuous flow. The primary difference between the two devices is that the metering unit has an internal check valve which opens under pressure. The metering unit will deliver a measured amount of oil to the component.
The check valve prevents backflow from the port. Most SLRs are equipped with small internal filters to reduce contaminant blockage at the metering device. The control unit has a helical cylinder (similar to a screw pump) that provides continuous volume-controlled flow to the component. System pressure and the size of the helical threads determine the total amount of lubricant. When the pump is brought online, it induces flow to a common header.
These systems are capable of pumping oil and grease up to NLGI #2 with a maximum pressure of 3,000 psi. There are two configurations: pump-fired/spring-primed, and its reverse, spring-fired/pump-primed. Pump-fired/spring-primed is the most common configuration, in which each component receives lubricant from the injector, powered by the host pumping station. When the lubricant is delivered to the bearing, the injector spring is used to re-prime the injector with lubricant for the next lube cycle. The advantage over a pump-fired system is that the delivery of lubricant to the bearing is fast and benefits from full-pump pressure.
With the spring-fired/pump-primed configuration, the pump is used to prime the injector (fill it with lubricant). When the spring is fully compressed, the header line from the injectors to the pump is vented to atmosphere. Lubricant is delivered to the bearing via the power of the spring. The mobile market has embraced the spring-fired system because it provides a slow delivery of lubricant. Injector-based systems can also be found in steel, paper and mining applications. They are considered robust in design and capable of surviving harsh environments like those found in steel mills and mines. Some spring-primed/pump-fired injectors are limited to a NLGI 1 or lower.
Piston Distributor Injectors
Piston distributor injectors (PDI) are parallel in design and are primarily used with oil and semifluid greases (NLGI 000, 00, 0). PDI systems are positive-displacement systems, capable of pressures to 800 psi. PDIs and standard injectors are similar in design and operation. Pump configurations can be pneumatically or electrically driven. The main differences are maximum system pressures and lubricant grades handled. Piston distributors have received notoriety in some automotive plants because of their low cost and flexibility in adding points.
The series progressive system is designed to accommodate system pressures up to 3,000 psi. This gives the user flexibility in system configuration and lubricant selection. Unlike parallel units that have multiple branches off a main line, progressive systems are plumbed in series. With the proper sensors, these can provide feedback if a line becomes blocked.
Figure 3. MSP Feeder Block
The general design consists of a master block, which distributes a controlled volume of lubricant to a series of secondary feeder blocks (Figure 3). The secondary feeders deliver a controlled volume of lubricant to each component.
The feeder manifold consists of a stack of output blocks held together by tie rods. Each feeder section contains a precision-fit spool sized to provide a fixed volume output for each block.
The blocks are made to have one of two possible output configurations, twins and singles. A twin block has two outputs of equal volume. The single block has only one output. The rated output is stamped on the side of each block for easy determination of the injector output. For example, a 20T block has an output of .020 cubic inches per each of two ports. A 20S has an output of .020 cubic inches for one port only. The output range is from .005 to .080 cubic inches. Contrary to popular belief, a series progressive system delivers lubricant to one component at a time. Each spooled feeder section depends on flow from the previous section to shift and displace lubricant. In other words, if one spool doesn’t shift, none of the other spools will shift.
A simple switch installed on any active spooled block to sense piston movement creates a closed loop system. The lube controller expects the switch to activate within a certain time interval. If the switch fails to cycle in the given amount of time, the system controller will indicate a system fault. While these systems can be intimidating to troubleshoot when a lube fault occurs, proper training on how the system works will provide maintenance personnel with the confidence to service the equipment properly, and accurately interpret and correct those faults.
Figure 4. Dual-Line Block
The dual-line or reversing system is used commonly in steel mills and paper mill applications. These systems can be open or closed loop; either manual, air or electric motor powered; and can handle hundreds of points at distances of several thousand feet. Basic systems are comprised of a pump, reversing valve, filter and various dual-line distribution blocks (Figure 4).
Two header lines are plumbed in parallel from the reversing valve to the lube points. There are two configurations in header design. With the closed loop design, the dual header lines run completely around the lubricated equipment back to the reversing valve. In most closed loop systems, the reversing valve is actuated by differential pressure from each header line.
With the end-of-line design, the header lines are run to the farthest point on the lubricated equipment and plugged. A pressure switch may be installed at the end of each header. When the pressure rises, the pressure switch is actuated and sends a signal back to the lube controller. This will shift the solenoid-actuated reversing valve. Shifting the valve allows lubricant to flow into the second header where the process is duplicated. Dual-line systems can distribute most lubricants, including NLGI 2 grease. Close attention to line size is important because flow depends on system pressure and oil viscosity (grease consistency).
Most multiport systems handle fluid greases from 000 through NLGI 2. The pump is normally an integral part of the reservoir with 4 to 72 lube points per system, depending on the manufacturer. For the Interlube brand, the pump and injectors are built into one housing underneath the reservoir. When the pump is actuated, one or more cams operate a series of injectors. Each time the pump is actuated, the cams will rotate. The cams activate the individual injectors to provide a positive displacement of lubricant. The color-coded injectors provide easy identification of lube output. Multiport systems can be operated with 12/24 VDC or 110 VAC electric pumps, hydraulic or pneumatic pumps. They are compact and easy to install, and are popular in trucking and off-road applications.
Electrical controls, programming, scheduled maintenance requirements and system flexibility requirements are some of the factors that affect the overall cost of lubrication systems. Selection of system type will impact overall costs. For example, a single-line resistance system in most cases can use low-cost poly tubing. Parallel systems with their single-line headers and injector manifolds offer reduced plumbing and simple installations. A series progressive system on the other hand, requires the mounting of individual feeder manifolds with connections from each manifold back to a master block. Setup time on these systems can vary from 30 minutes to several hours, depending on how difficult it is to air purge (bleed) each lube line.
There are many equipment relubrication options available to the industrial or fleet operator. This partial list shows popular approaches to relubrication at various stages of complexity (Table 2). Limits for system selection include the number of individual points to be lubricated, whether components are to be oil or grease lubricated, the type of lubricant to be selected, the total distance between the points, and finally the amount of capital that the operator has available to dedicate to the task. An effective design and the effective training of maintenance personnel can assure long-term cost-effective, consistent relubrication of plant equipment.