Maintenance personnel in industrial plants and facilities know a great deal about pumps. They can replace seals and bearings in a jiffy, remove and install pumps and generally fix anything that goes wrong mechanically. They know how, because many of them do it a lot—on the same pumps, month after month.
Plant engineers know how to read a data sheet and (often with the help of a pump manufacturer) can spec pumps to meet flow, pressure and service requirements. Pumps can be properly sized initially for ideal conditions when a system is designed. The only problem is those conditions in the process are dynamic and rarely stay the same over the life of the pump, so it may not be the ideal pump size for the conditions five years from now.
But it can be difficult for these maintenance technicians and plant engineers to tell when a pump is having problems, performing badly or is about to fail. So many pumps run to failure. A big part of the problem is the lack of sensors on many pumps, resulting in insufficient data to detect common problems, such as:
- vibration that can damage pumps, pipes and foundations
- cavitation that can destroy impellers and volutes
- “dead head” operation (zero flow) that can overheat the liquid, maybe causing the liquid to flash to vapor
- seal pot leaks of toxic, hazardous
- or corrosive fluids
- excessive pump case pressure or pressure spikes that can damage pump seals
- excessive temperature within a motor that can cause damage
Without flow, pressure or temperature sensors—and the knowledge of what to do with the data provided by these sensors—many pumps fail unexpectedly and upset processes, use too much energy or require excessive maintenance.
And when a pump fails, it can shut down a process or an entire plant, cause spills, fires or explosions and harm personnel. The solution is twofold: add instrumentation to pumps, and train maintenance personnel and engineers on how to diagnose pump problems using data from the instruments.
Most pumps already have (or should have) a flow meter to monitor pump discharge flow rates. Pumps also need a differential pressure (DP) instrument and a temperature instrument. A DP instrument can monitor the suction and discharge pressure—i.e., the differential pressure—of a pump. Too high or too low suction and discharge pressures can cause or indicate various pump issues such as cavitation, loss of flow, mechanical failure, vibration issues, excessive noise, or bearing and sealing wear. And some newer electronic DP devices have built-in temperature measurement capabilities (see Image 1). Temperature instruments can measure pump, fluid and motor temperatures.
Monitoring the suction head identifies conditions that can damage the pump.Several factors can change the NPSH required, including increases in flow rate and changes to the pressure or liquid level in a supply tank in front of the pump. “Smart” flow meters are available that can diagnose problems such as entrained air, vibration (which could be caused by pump cavitation), coating, corrosion and inhomogeneous or unsuitable media (see Image 2).
Data from a Coriolis flow meter can detect an empty pipe, density shift, temperature shift and other conditions.
Data from flow, temperature and DP instruments is sent to the control system and routed to pump analysis software. This software—which is available in many asset management, condition monitoring or maintenance platforms—typically incorporates pump curves from all pumps being monitored. This lets the software compare the pump’s actual performance to what it should be.
Pump software is also available from the Department of Energy (DOE). The Pumping System Assessment Tool (PSAT) is a free online software tool to help industrial users assess the efficiency of pumping system operations. PSAT uses achievable pump performance data from Hydraulic Institute standards and motor performance data from the MotorMaster+ database to calculate potential energy and associated cost savings. It can be downloaded at www.energy.gov/eere/amo/articles/pumping-system-assessment-tool.
The savings from reduced maintenance, longer pump life, fewer process upsets and improved efficiency far outweigh any modest investment in pump instrumentation.
Training the Pump Experts
Even if pumps are instrumented properly and the data from these instruments is analyzed with a pump monitoring system, the engineers and maintenance personnel may not know what to do with the data without proper training. In some cases, the instruments indicate a problem, but expertise is needed to determine the best fix.