Pump monitoring: Measuring flow without a flowmeter?
|PumpSmart provides a range of functions to monitor operation and protect the pump in the event of upset conditions or dry running.|
When working with positive displacement pumps, calculating output flow is simple in that speed and output are directly linked. Each shaft rotation effectively puts out a specific amount of liquid. Centrifugal pumps aren’t as simple. Most run at fixed speeds and work off a pressure/volume curve which provides only maximum limits. Putting a pressure gage on a pump discharge might give some sense of flow rate, but probably wouldn’t be very accurate. ITT has developed a software suite called PumpSmart that has a number of useful features, but one particularly interesting function called SmartFlow says it can calculate the flow of a variable-speed centrifugal pump within
Compared to standard instrumentation, accuracy ofted speed, and power at shut-off. ITT says these data can come from supplier catalog information without any actual testing. A self-calibration function takes into account changes in mechanical and volumetric efficiency losses to separate the true hydraulic load and calculate actual pump flow, all without any external sensors.
Working with other functions in the suite, PumpSmart can use the information gathered to control pump operations, particularly those with flat head-capacity curves. Small changes in speed can cause large changes in flow which makes pump control loops hard to tune. The software reportedly solves that problem by controlling torque more than speed, which creates a steeper curve that is easier to regulate. The ultimate effect is more stable control, without the tendency to oscillate around the setpoint. In this context, flow accuracy of
These functions are only part of the justification of PumpSmart, according to Dan Kernan, product manager for ITT. ‘It’s all about energy and reliability,’ he says, ‘PumpSmart uses VFD capabilities to run a pump at optimum efficiency.’ The lifecycle cost for a typical ANSI pump, in service for 15 years, breaks down to: 32% for maintenance, 44% for energy, 16% for installation, and only 8% for the original purchase price. Anything that can reduce energy consumption and maintenance will have a huge impact on overall cost.
Control Engineering Daily News Desk
Peter Welander , process industries editor