Properly Store Your Lubes

Greases usually are shipped in one-time-use drums or pails. It is not uncommon to convert those containers to working reservoirs, as with this auto-grease lube system. Photo: Engtech Industries Inc.

Totes and working reservoirs are key components in any lubricant-storage system.

Webster’s dictionary defines the reservoir as “a place where something is kept in storage, such as a part of an apparatus in which a liquid is held.” When that liquid is a lubricant or hydraulic fluid, two specific categories are employed: storage and production, or working, reservoir.

Storage Reservoirs

In their simplest form, lubricant reservoirs are pure storage containers used to transport and hold lubricants for later transfer into smaller working reservoirs. Practical examples include tanker trucks that deliver oils to a site, which are then, in turn, often transferred into interim on-site storage reservoirs. The most commonly used on-site storage reservoirs are 300-gal. (1,200 liter) polyethylene totes. These totes are popular because they never rust and their light color makes it easy to visually determine oil fill level. Due to their light/somewhat flexible wall construction, poly totes are often contained in steel frames to prevent the walls from bulging under load. This also allows them to be stacked in storage locations.

Grease-storage containers differ in that greases are commonly sold and delivered in one-time-use drums and pails. The grease is transferred manually or by external pump at a later time to a machine or working grease lube system reservoir. The drum or pail can also be used as a replacement working reservoir by simply mounting the machine lubrication pump to the container. Grease cartridges are mini reservoirs, viewed as single-use cassette-style reservoirs that, once loaded, convert a grease gun into a greasing pump/system.

Typically, storage-style reservoirs are simple box- or tube-style vessels that contain a lid or large capped opening for bulk-fill purposes. Oil-storage reservoirs will often be equipped with a drain port for draining off moisture. Oil is typically bulk loaded through a fill port using an auxiliary pump. Gravity is used to dispense lubricant through a tap valve mounted in the lower region of the reservoir.

Storage reservoirs are rarely filled 100%. As the fluid level falls, the resulting “head space” volume between the top of the fluid and its roof becomes larger. This space will tend to accumulate water and solids contamination caused either by ambient heating and cooling cycles and/or open filling of the reservoir. To minimize contamination, a desiccant-style breather installed in the reservoir roof is recommended. This style of breather allows air to flow in and out of the reservoir, thereby neutralizing any tank pressure and capturing moisture and solid contamination in the breather filter media.   

Working Reservoirs

The most common device used to store oil is a 300-gal. polyethylene tote, encased in a metal frame. The metal frame makes it possible to stack the totes. Most have an opening at the top for bulk filling and a tap valve at the bottom. Photo: Engtech Industries Inc.

Working reservoirs are most often integral to the machine, system, or lubrication pump they are designed to support. Consequently, their design is more critical and complex than a storage reservoir, primarily because their footprint must fit in the space made available by the machine, system, or pump design. In addition, their design must accommodate a variety of system control demands noted below.

When a closed-loop recirculating oil system is used, a design balance is struck between the bearing lubrication requirements, the size of the lubricating pump, and the size and shape of the lubricant reservoir. Reservoir sizing is critical, nonetheless. The reservoir must be large enough to accommodate the lubricant needs of the bearings and delivery-piping system while the machine operates at full load and must also accommodate all of the returned system oil when the machine is at rest.

In a recirculating-oil system, the oil is “washed” over the bearing to lubricate and cool the unit. Cooling is performed by transferring heat from the bearing to the oil, which is returned to the reservoir. Part of a working reservoir’s job is to allow the oil to cool considerably before being pumped back to the bearing for its next cycle. This is achieved by using internal tank baffles that force the oil to travel slowly across the reservoir from the return to the delivery side using the reservoir and baffles as a heat sink to transfer and dissipate oil heat. Rapid cooling is achieved by using built-in radiator-fin-style exchange cooling circuits.

A working reservoir is likely to have an internal screen-type suction filter plumbed to the pump delivery line. Most reservoirs will indicate lubricant level using a plumbed-in external site gauge, which could also be sensor connected to an alarm or smart signal-receiving device. Total-loss oil systems can use low- and high-limit reservoir fill sensors that also auto activate a solenoid fill valve connected to a storage reservoir, allowing the unit to fill automatically as long as oil is present in the storage reservoir.

Similar to storage reservoirs, one would expect to see a desiccant-style breather in use when the reservoir is atmospherically pressured. A closed-tank system is used when a reservoir is to be positively pressurized as in a spray-type lube system.

In its basic form, a working reservoir is filled through a simple capped fill port that is easily prone to contamination ingress during the filling process or by forgetting to refit the cap in place after filling is complete. Newer systems use direct connect/disconnect fittings that, when connected to compatible filter carts, allow the reservoir to be filled with the cleanest oil possible. The same system can also be used with the filter cart to perform an “off-line” bypass cleaning through the cart filter, often while the machine is running, returning it directly into the reservoir, saving money and downtime on regular oil changes.

When located outdoors in cold climates or unheated winter conditions, many reservoirs are fitted with thermostatically controlled electric heat plugs, similar to those used in automotive engine-oil reservoirs, to ensure the oil always operates in its optimum viscous range.

Reservoirs are much more than simple tanks. If they are to continue to operate reliably, they must receive regular attention as part of any lubrication system preventive-maintenance program. EP

Contributing editor Ken Bannister is co-author, with Heinz Bloch, of the book Practical Lubrication for Industrial Facilities, 3rd Edition (The Fairmont Press, Lilburn, GA). As managing partner and principal consultant for Engtech Industries Inc., Innerkip, Ontario, he specializes in the implementation of lubrication-effectiveness reviews to ISO 55001 standards, asset-management systems, and training. Contact him at kbannister@engtechindustries.com, or telephone 519-469-9173.