Example of case drain observation interval with respect to pump age.
Through strategic monitoring of the case drain flow and other systematic measures, personnel can address pump maintenance requirements prior any excessive degradation or fragment failure modes. Unfortunately, plants that depend on the reliability and continuous operation of pumps in various systems are most drastically affected by extended periods of system downtime. Under such circumstances, it is crucial to anticipate and plan for failures. Excessive costs or down-time periods are simply not acceptable. Adoption of pump case drain to reservoir flow monitoring as part of a predictive maintenance program warrants consideration. This is not to say that non-mission critical plants will fail to benefit from the monitoring of case drain flows as part of a strategic maintenance and diagnostic program. Plants that depend on reliable operation of the equipment in question are generally less able to maintain production capacity in the event of unexpected system downtime.
Proper meter selection
Choosing pump case to reservoir flow monitors for different pump designs or configurations is left to the discretion of the user. Familiarity with the pump and its operation in the system is important. You must consider the pump's mode of operation as well as any other device that could use the main pump case as a path to divert flow back to the reservoir. The case drain monitor is designed for straightforward use as long as application and installation details are addressed.
First, determine the flow rate of the application. This effort typically involves calculating 10% of the total output of the pump and choosing the closest flow range. Sizing the monitor correctly makes it easy to take readings at the flow rates required, and the pressure loss due to the meter will be minimized. In many cases the reading that results will not correspond directly to an offered flow range, so rounding up to the nearest range is recommended.
If the case drain monitor presents a restriction in the case-to-reservoir drain line, exceeding that dictated by manufacturer recommendations, an installation in tandem with a low-cost bypass valve could be considered. This type of configuration would allow the person taking the measurement to temporarily divert flow through the meter and then straight back to the reservoir.
Rob Copsey is a mechanical engineer at Lake Monitors Inc., Milwaukee. Contact him at [email protected] or visit www.lakemonitors.com. He acknowledges the contributions of Rory McLaren, of the Fluid Power Training Institute, and Applied Industrial Technologies in preparation of this discussion.