These workhorses (aka SPLs) may not be right for every application, but they have a rightful place in every plant’s lube-management program.
Anyone who has visited the engine room of an old steam ship or watched an old steam engine run will have seen a beautiful brass and glass chamber full of oil sitting directly atop each major bearing point. These pioneering single-point automatic lubricating devices were elegantly simple—the majority of them operated by cracking open a tapered valve to a determined point to allow oil to flow by gravity onto a transfer wick or brush in contact with the bearing surface.
In 1872, while working as an oiler for the Michigan Central railroad, Elijah McCoy changed the lube game considerably when he invented the world’s first automatically pressurized (non-gravity activated) lubricator that used steam from the engine to activate and force-feed lubricant from the device to the bearing surface. So successful was McCoy’s patented device that the railroad companies shunned all other designs in favor of it, coining the phrase by wanting only “the real McCoy!”
Incorporating a similar design, grease can also be success-fully dispensed using gravity and the aid of a spring-ten-sioned follower plate inserted in the lubricant chamber. Grease is filled from the bottom of the reservoir via a nipple that allows grease to hydraulically push against the follower plate and spring to load the chamber. Once loaded, the grease is expelled by the spring-loaded chamber pushing the grease against the hydraulic back pressure set up by the bearing clearance. The bigger the bearing, the bigger the clearance—and the more grease expelled into the bearing area.
Although expressly designed as a one-bearing, one-point system, the gravity lubricator could be (and often was) coupled to a single-inlet, multiple-outlet manifold to lubricate multiple points simultaneously, albeit in a non-metered manner. As a testament to their design, these early Single-Point Lubricators (SPLs) are still available for sale, with many original lubricators still in use today largely due to their simplicity, quality of manufacture and ability to be refilled easily by the user (see Fig. 1). Their successors are in a different league, however. Today’s models are sophisticated units that use chemical, electro-chemical and electro-mechanical pumps controlled by built-in electronics to move oil and grease at pressures great enough to use progressive-styled metered divider-block delivery systems.
How the System Works
One of the earliest innovators of the modern styled SPLs was the German company Perma, which developed an inexpensive disposable chemical-activated design in the early 1960s. This simple unit uses a chemical reaction to develop a gas contained within a sealed expandable bellows unit. The maintainer activates the unit by releasing a fixed chemical charge pellet into the bellows that is forced to react with an electrolyte to produce an expandable gas. As the gas slowly expands within the bellows, it pushes the lubricant out of the unit into the bearing area. Different chemical charge amounts are used to vary the dispensing time from days to months, depending on the bearing’s needs. With a 4oz (120ml) reservoir, this style of unit—in its current updated version—continues to be one of the most popular SPL units for the dispensing of grease.
Almost 20 years later, in the early 1980s, we saw the first electronic-controllable SPL from ATS Electrolube. Using an electro-chemical reactor cell, the user activates the unit via a series of time-selector switches connected to a battery-operated electronic circuit board (see Fig. 2). Once activated, a pulsed electrical current is sent through a contained electrolyte causing an electro-chemical reaction. This reaction creates an inert nitrogen gas to form inside a hermetically sealed bellow that pushes against the oil or grease charge contained in the lube reservoir section of the unit. Unlike the chemical-activated style, the discharge on this unit can be controlled or turned off completely by the circuit-board selector switches. Like its chemical-activated cousin, this is also a single-use disposable unit, as the bellows cannot be collapsed. Modern modified variations of this design now allow for a refillable reservoir with only the power unit and bellows requiring replacement when exhausted. Offered in many reservoir sizes, the most popular size continues to be the 4oz (120ml) unit.
Fig. 2. Time-selector switches on an electro-chemical type of SPL (Courtesy Engtech Industries, Inc.)
One major drawback of the two previously described designs is their inability to deliver controlled lubrication to multiple points. The original gravity lubricators had but a single point of control and residual line pressure; the chemical and electro-chemical lubricators only developed between 50 and 60 psi. The latest generation of SPLs addresses these issues with a battery-operated rotary mechanism driving a positive displacement pump that delivers output pressures from 350 psi to 900 psi—more than enough to move a small, multiple-outlet series-progressive divider valve built into or piped remotely to the pump. Unlike previous designs, the core units on the latest models are reusable with refreshed lubricant and batteries. Still very affordable, these new-style devices offer a viable centralized-lubrication-system alternative to the bigger systems with which they now compete.
Pros & Cons
The early gravity units were developed to relieve the continuous attention required from the lubricator, whose job was to check the units’ reservoir levels and fill them as needed while the bearings reaped the benefit of continued lubrication in small amounts. The advent of automated units allowed out-of-sight bearings—such as those found on overhead cranes or roof-top units—to receive continued lubrication for weeks or months, again relieving the burden on the lubricator whose role changed to checking and marking the lubricator reservoir and performing a unit change-out when required. For no capital outlay, these low-cost units have extended the life of many bearings over the years.
Because individual units are inexpensive and convenient, many maintenance departments fall into the trap of using them on every bearing with a grease nipple. Performance notwithstanding, widespread indiscriminate use can get very expensive, very quickly. Their use should be monitored against the cost of implementing the more expensive electro-mechanical SPL with hard-piped-divider delivery systems, or one of the more robust standard types of centralized systems that can deliver lubricant to hundreds of points simultaneously.
Fig. 3. An electro-chemical lubricator with “Date in Service” clearly indicated (Courtesy Engtech Industries, Inc.)
Tips for Use
Single-Point Lubricator technology is an example of a very real (and long) industrial success story. SPLs are here to stay—not for every application, of course, but as a valuable tool in every plant’s lubrication-management program.
The next article in this delivery-systems series will focus on Pump-to-Point designs. Look for it in the March/April issue. LMT