Last month, we ended our discussion of proportional control by saying there are times when P alone cannot provide the accuracy required by a process. Take, for example, a constant pressure booster system under VFD control. If changes in flow and the resulting change in pressure occurred gradually over a long period of time, the VFD could use proportional control to keep pressure constant.
Soft starters and VFDs are useful for extending equipment life in HVAC applications.
It required only a couple notes of the haunting soundtrack to signal an imminent shark attack in the movie Jaws. As the theme began to swell, it became obvious that someone was going to “get it.” It would be nice to have a sixth sense that allowed us to hear "warning" music in daily situations. Condition monitoring systems provide a means of sensing when sharks are skulking toward your critical machines.
Water chemical compatibility and electrical interference are two major challenges for control systems. Two major sources of fresh water can limit the performance of the control system.
Although the use of transmitters in pressure measurement is growing, mechanical pressure gauges are still used on most systems as local pressure display to back up electrical readings. The selection and installation of these gauges can be difficult in certain locations. Harsh conditions that can require special consideration include vibration, pressure pulsation, overpressure, corrosive media and extreme process and ambient temperatures. This article is designed to address harsh conditions with best practice recommendations to extend gauge life and provide for the safest installation possible.
Last month we reviewed the pump selection criteria for a closed loop circulation system (Vp-Vf). This month we will take a look at a similar application that adds some elevation to the equation.
One of the major contributors to unbalance in rotating machinery is eccentricity. When we disassemble parts, we must also reassemble them. Even if the reassembly requires heating to shrink-fit the elements back together, we probably balanced them in a balancing machine where tolerances due to fit-up on mandrels or roundness of journals may possibly far exceed the heavy spot tolerances that the target standard of balance allows.
PWM inverters introduce motor shaft voltages and bearing currents. The bearing damage in inverter-driven motors is mainly caused by the shaft voltage and bearing currents created by the common-mode voltage and its sharp edges . All inverters generate common-mode voltages relative to the power source ground that cause coupling currents through the parasitic capacitances inside the motor. The main source of bearing currents is the capacitance-coupling currents that return via the motor bearings back to the ground.
Even when a redundant pumping system is in place, it can be advisable to monitor the condition of the operating units in critical applications where maintaining production depends on motor-pump reliability.
Mechanical pressure gauges, which require no external power, provide an affordable and reliable source of accurate pressure measurement. Using the criteria below can help maximize gauge life.
Interpretation of equipment clues can help diagnose problems before failure occurs
Changing traditional industry ways of thinking can help usher in the plant of the future.
In only a couple of years, the focus on energy efficiency has gone from blurred to steely-eyed. Green business practice is now a necessity, and organizations must find the best way to transition to this new reality. There are many opinions and approaches on "how we get there," and each one will have its own merits. A journey of a thousand miles starts with a single step, and making the right steps in the beginning will hasten the achievement of energy efficient goals.
The installation of an AC drive with an advanced software tool has dramatically cut call-outs for blockages at an Irish county council pumping station.
Determining the correct maintenance strategy for industrial production assets poses a problem for many plant asset managers and reliability and maintenance engineers.
The Detroit Water and Sewerage Department (DWSD), a municipally owned utility, provides roughly four million residents in southeastern Michigan with an average of 710 million gallons of water per day.
Potential to Failure (P-F) curves graphically display the failure time cycle and measurement techniques that can be used to detect asset failures prior to reaching the asset incurring functional failure. Proactive strategies should focus on managing assets high on the P-F curve, or early (P1 to P5) in the failure cycle (Figure 1). The ability to detect failures early in development allows top quartile performers to proactively manage their maintenance programs by understanding the health of their assets. Many companies, however, find it difficult to operate proactively and continually react to assets that reach functional failure with little or no warning.
How a monitoring alarm system with control and shutdown capabilities prevented costly pump damage and environmental hazards and made the job of the pump operator safer and easier.
With the wide use of variable frequency drives in the pump industry and increasing unit size, it is becoming more difficult to design mechanical systems free from natural frequencies within operating speed range. If such an occurrence is allowed in the field, a resulting resonance condition threatens to significantly impact performance and longevity of the equipment.
Pumps are sent to rebuilding and remanufacturing companies because buying new can be expensive and require long lead times. For instance, a 39 in diameter, 1,000 lb bronze impeller may cost $28,000 and take many weeks to deliver. In these cases, the impellers involved in an overhaul are often built back up to the required specifications and rebalanced.
Back in the old days, level control had little or nothing to do with saving energy. In fact, it was often a necessary evil. Today, that is no longer true - the VFD offers the potential for power savings in lift station applications that range from a few hundred gallons per minute to those that have to move thousands of gallons each minute.