Pumps are essential in transporting fluids, slurries or gases (compressors) in industrial plants, municipal water and wastewater systems, and chemical processes. With the help of energy provided by the mechanical action of the pump, the compressed or pumped fluid moves from high pressure to low pressure. Regardless of whether the pump is a rotary pump or a positive displacement pump, the goal is to convert mechanical energy into fluid energy. In most cases, the prime mover is an electric motor or engine that rotates the shaft at high speed to add energy to the fluid to be moved.
The bearings supporting the shaft must be lubricated to reduce friction, increase efficiency, and prevent wear. When the lubricant is grease, the lubricant also plays a key role in sealing the bearing, preventing particles from the environment or contaminants from the fluid on the high-pressure side of the pump from entering.
Sometimes the pump OEM will provide guidance on grease selection. Generally, unless the user is proficient in lubrication, the language is vague and unhelpful. For example, a pump OEM might say, “Let it be lubricated with a high-quality National Lubricating Grease Institute (NLGI) 2 lithium grease.” In any given factory, there may be multiple types of lithium or lithium complex thickened lubrication fat. But how do you define "high-quality NLGI 2 grease"?
Experienced maintenance professionals may rely on previous practices or lessons learned from trial and error schools to find feasible solutions. Just because grease solutions have worked in the past, can future success be guaranteed? Is the work solution optimal? NLGI recently launched a new grease specification designed to provide guidance and support for determining quality and performance levels. Maintenance and operators can use these greases to select greases that are suitable for their applications and enhance confidence.
The NLGI High Performance Multipurpose (HPM) grease specification is a performance standard for industrial applications, parallel to the long-running GC-LB classification system introduced by NLGI in the late 1980s, specifically for automotive chassis and wheel bearing greases. The HPM specification encompasses two major areas: manufacturing consistency/quality and application performance expectations.
Since grease is manufactured through chemical reactions and mechanical processes, it is important to ensure that the finished product meets manufacturing standards for mechanical stability, oil separation, and NLGI conformance. The HPM specification sets constraints that define the expectations that users can rely on when purchasing grease that meets the HPM specification.
Performance expectations vary depending on the intended application of the grease. The HPM specification sets benchmark performance standards in terms of seal compatibility, load carrying capacity, starting torque (-20 C/-5 F), and closely related waterproof and corrosion protection.
In order to maximize efficiency and component protection, the viscosity of the selected grease base oil is the most important consideration. This is determined by the bearing size, speed and operating temperature. If the OEM has considered these items, users can follow it and succeed. If the guidelines are ambiguous or specific operating conditions are difficult, users may need to go deeper to find the best solution.
Similarly, users can consult the NLGI HPM specification for guidance. The HPM specification includes recognition of enhanced performance that may be applicable to specific pump conditions-corrosive media, the possibility of excessive water ingress, vibration or extreme temperatures. The endorsement is:
In addition, the fretting protection by the other two methods (ASTM D7594 and D4170) is also considered.
As an industry body, NLGI is brand and marketer neutral. Although the NLGI membership consists of representatives of grease manufacturers and marketers, there are additives and raw material suppliers among its members, which in many cases bring balance and perspectives. The HPM specification process includes these membership classes. Marketing and manufacturers include large integrated oil companies as well as specialty grease companies and third-party manufacturers. Both parties agreed that the HPM specification should be challenging but achievable, set a common performance expectation, and provide guidance for end users. The process involves multiple iterations between NLGI members and consultants to determine performance limits and acceptance criteria.
Grease selection may include many aspects—for example, brand, value, availability, and local service. Sales and marketing materials from various sources can be confusing or even difficult to resist. The HPM specification is designed to provide end users with common performance expectations, thereby providing a certain degree of confidence in the performance of the product in a particular pump application. Other criteria can help narrow the user's product choices and purchasing decisions.
The water treatment facility has multiple centrifugal pumps for transporting water, treating corrosive treatment chemicals and waste sludge. The facility is located in the Chicago area, where the pumps are in use both internally and externally and are exposed to the natural environment. Sludge pumps have built-in redundancy, so they run intermittently. Plant operators hope to increase plant uptime, reduce maintenance costs, and simplify lubrication tasks. Based on this scenario, what should the operation and maintenance personnel do? The selection process may be as follows.
Once maintenance personnel have identified potential performance challenges, HPM base grease is a good choice. However, a better choice is to choose a grease that provides performance even when exposed to corrosive process chemicals (HPM + CR) and excess water (HPM + WR). Considering that the pump may face low temperatures when starting, low temperature grease may be a wise choice (HPM + LT). By choosing to refer to the NLGI HPM specification, the basic performance can be determined. The additional recognition of CR, WR and LT will allow employees to choose a product that can alleviate all performance barriers and simplify their lubrication procedures by combining all pumps into one product.
Protecting pump components, reducing operating costs, and simplifying grease selection are all valuable and achievable goals. Using the NLGI HPM grease specification can help users achieve these goals. By consulting lubricant suppliers and asking them to provide quality and performance that meets NLGI HPM standards, grease users can set and exceed expectations when choosing a grease to lubricate their system.
Greg Morris is Shell's grease application specialist for the Americas. He has a bachelor's degree in chemistry from West Virginia University and 30 years of industry experience. He is currently a member of the NLGI Board of Directors, serves on the Research and Education Committee, and participates in the Technical Committee.