Metropolitan Industries Inc. is proud to announce that the company has been issued a system and method patent by the U. S. Patent Office (No. US 8,180,496 B2) which will allow dissimilar variable speed pumps to be controlled in a way never before possible. We have elected to market our programmable logic control systems utilizing this technology by using the term “load sharing.”
The development of load sharing should be very welcome news to anyone attempting to operate any liquid transfer or pressurization system through the use of dissimilar pumps or other challenging hydraulic scenarios. The load sharing process allows Metropolitan to manufacture specialized variable speed control systems for pumping applications which have multiple dissimilar pumps or pumps which need to operate together under varying hydraulic conditions.
Load sharing will eliminate conditions during which one or more pumps operate under high or extremely high energy load conditions, while other pumps within the system are extremely under loaded electrically. These operating conditions are undesirable because they typically cause the pumps to operate well outside of their zone of peak hydraulic efficiency. Load sharing, in essence, is a way of ensuring that all dissimilar pumps within a system tend to operate at peak hydraulic efficiency, regardless of the hydraulic load of the process they are feeding, the hydraulic conditions under which they are operating, and the varying load profile of each pump.
Load sharing defined:
Load sharing is a dynamically-equalizing process by which two or more dissimilar pumps, with dissimilar hydraulic characteristics or operating under dissimilar hydraulic conditions, are operated in unison to accomplish a common task, while drawing a commonality of electrical energy proportional to their individual load characteristics. The process is dynamic because the electrical power load of each pump on the system is continuously compared to the maximum load of the unit. In addition, the electrical power load of each individual pump is also continuously adjusted in proportion to each of the other units, so that the percent load of each unit is proportionally matched by all other units. As such, each of the pumps on the system will very likely operate at rotating speeds which differ from one unit to the next, while attaining the exact same desired set point task.
Common task clarified:
The grouping of pumps must be programmed to accomplish the same set point task, whether the task is to maintain a common line pressure, maintain a common outlet temperature, maintain a common pumped water elevation or, in some instances, a combination of two of these tasks.
Commonality of proportional energy explored:
The load sharing program will adjust the speed of each pump individually while maintaining the common task set point(s), so that the power load (or kilowatt consumption) of each pump in the group is proportional to the load of all pumps in the group.
Example scenario: One 20 HP pump will operate at 10 BHP, while two 60 HP pumps each operate at 30 BHP. In this scenario, each pump in the system operates at 50 percent of its peak load. This process dynamically and continuously varies proportionally, as the demands of the pumped process changes.
Real world examples:
The load sharing process we’ve patented is designed to be very flexible, allowing the technology to be adapted to a variety of applications. The technology will provide us with the unique ability to tackle some of the most challenging hydraulic scenarios in the markets and industries we serve.
Multiple pumps with dissimilar flow capabilities:
One or more smaller jockey pumps (or lead pumps) can operate with one or more larger duty pumps (or lag pumps). Possible examples would be a water pressure booster system for a large commercial building or, potentially, a municipal water pumping station. Pumps of various rated flows can work together, each with a shared proportion of their rated horsepower.
Multiple pumps with dissimilar performance characteristics:
One or more pumps with “steep” curve characteristics can operate with one or more pumps with “flat” curve characteristics. This is the perfect process control in a scenario where one or more multi-stage pumps need to operate in conjunction with one or more single-stage pumps.
Multiple pumps, at different geographic locations, feeding a common process:
A municipal pumping station at the east end of town can operate in unison with another pump station at the west end of town. Load sharing is a great solution, especially if the pump stations are at different elevations. Managing this type of application is also enhanced if the water main friction loss profiles are also very different at each end of town.
Multiple pumps, with different suction pressures, feeding a common process:
An exceptionally difficult process-control scenario can be overcome with relative ease. A municipal pumping application, including two or more gravity tanks at varying elevations, feeding a multiple pump system, with a single set point pressure, is an excellent application for load sharing technology.
Multiple pumps with dissimilar motor sizes:
By the nature of the pumps described, many of the scenarios mentioned above will inherently include pumps with various motor sizes. Load sharing will allow all of these systems to operate at their proportionally equal power load, which in itself will tend to ensure operation within the peak efficiency range of their individual performance curves.
Make no mistake: This process program is extremely unique and will be a very valuable asset to our clients while operating their most challenging pumping applications.
For more information regarding load sharing and any potential projects which may benefit from the process, please contact Metropolitan Industries senior systems engineer Brendan Bates at 800-323-1665 or firstname.lastname@example.org.