Pumping systems perform many important functions in modern built environments. In addition to delivering potable water, they are used in fire protection systems, industrial processes, and many types of HVAC installations. Pumps have both electrical and mechanical components, and are often subject to a high workload. Therefore, adequate maintenance is very important.

Pumps are normally driven by electric motors, but use a combustion engine in some applications. Although many performance issues affect the pump itself, malfunctions can also be the result of motor or engine issues. When a building experiences low flow or other pumping problems, an inspection from a plumbing engineer is recommended to find the cause.


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Preventing Impeller Damage from Cavitation

Cavitation is an hydraulic phenomenon where bubbles form in moving water due to pressure drop, and it normally happens when water reaches the pump suction at low pressure. Although bubbles may seem harmless, they produce small shockwaves when they collapse, and they can severely damage pump impellers over time.

One of the most common signs of cavitation is its characteristic sound, which gives the impression that water flowing through the pump contains rocks or marbles. The sound is actually caused by the shockwaves from collapsing bubbles.

Cavitation can be prevented with adequate selection of the pump and its piping, ensuring that water pressure never drops to the point where bubbles form. The pump’s location in a building also influences cavitation; pumps in upper floors are more likely to be affected, since water loses pressure as it flows upward towards the pump.

Preventing Electrical Issues in Pumping Systems

Even if a pump is in good condition and its piping is of the right diameter, electric motor issues can affect performance:

  • Adequate voltage must be supplied to the motor, or otherwise it will tend to overheat. Note that both overvoltage and undervoltage shorten the service life of motors.
  • In the case of three-phase motors, the voltage supply must have balanced phases. Voltage imbalance is also detrimental for motor performance and service life.
  • The motor’s electrical protection must be adequate for the application. Consider that motors draw a high inrush current when they start, and protection devices must tolerate this current peak without tripping.
  • If the pump uses a three-phase motor, it may be running in reverse due to an incorrect connection. However, this should not be an issue if the pumping system is installed by professionals. The rotation of a three-phase motor can be reversed by simply switching two of the three live wires.

There are also cases where the pump motor is operating correctly, but the unit is very old and inefficient, causing higher electricity expenses. Significant savings are possible by upgrading to a NEMA Premium Efficiency motor, especially if the pumping system operates continuously.

Minimizing Noise and Vibration

A certain level of noise and vibration is unavoidable when dealing with mechanical systems, and even high-quality equipment with adequate maintenance produces them. However, when noise and vibration levels are excessive, they are a clear sign that the pumping system must be inspected and serviced.

As explained above, if noise from the pumping system sounds like marbles in the water stream, cavitation is the most likely culprit. The issue must be solved as quickly as possible to prevent severe damage to the pump impeller.

In pumping systems, a common cause of vibration is misalignment between the pump shaft and the motor shaft. Vibration can also be caused by pump or motor elements that are mechanically imbalanced.

  • Misalignment can be prevented or corrected with high-technology methods such as laser shaft alignment.
  • Pump impellers can be balanced by removing material, normally with drilling. This leads to a uniform mass distribution around the shaft centerline.
  • Note that impellers can become imbalanced due to physical damage, which is often the result of cavitation.

Vibration increases the forces experienced by many pumping system components, shortening their service life. Vibration problems become worse when the pumping system has worn-out bearings, since they cannot provide adequate support for the rotating shaft.

Reducing the Electricity Consumption of Pumping Systems

A pumping system can operate correctly with poor energy efficiency, but why pay higher electricity bills when you can have efficient pumps? As previously mentioned, significant savings are possible by replacing old motors with NEMA Premium Efficiency Motors.

For even better results, you can add variable frequency drives (VFD) to control pump speed. Conventional pump control methods use valves to restrict or recirculate flow as needed, but this represents a waste of pumping power. On the other hand, speed control can provide adequate flow and pressure without control valves.

Professional MEP engineers can identify pumping system issues and propose the best solutions, as well as energy efficiency measures to reduce pumping costs.

 

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