September 2021

50 n SERVICE AND REPAIRS September 2021 www.drivesncontrols.com Preventive maintenance can avoid pump failures T he maintenance requirements for industrial pumps depend on several factors, including the type of pump, the clarity and viscosity of the substance being pumped, and the compliance requirements of the application. However, all industrial pump systems need regular maintenance to minimise costly, inconvenient, and possibly hazardous, unplanned downtime. Take the dairy industry, for example. If the pump seal in a UHT milk pasteuriser fails and a maintenance engineer cannot repair it quickly enough, an entire production batch can be lost. Now, imagine the same happening in a chemical processing plant where a pump is transporting hydrochloric acid for pH balancing – in this case, failures could lead to more than just financial losses. In both examples, careful inspection of the seals could have identified the early signs of damage and avoided catastrophic failure. Testing efficiency Despite the clear advantages of preventive maintenance in terms of cost, improved efficiency and increased safety, emergency repairs seem to be the prevailing method of caring for pumps. Owners of these machines should instead take advantage of modern testing and condition-monitoring systems, such as pump performance testing and vibration analysis. A pump performance test can measure the efficiency of the complete pumping system, defined as the ratio of the water kW and the brake kW delivered to the pump shaft. In a pump performance test, the level of efficiency is represented by a curve that indicates how the pump works regarding pressure and flow. One of the parameters measured by the test is the best efficiency point (BEP) – the point on the curve that leads to the most efficient operation. Efficiency will be at zero when the discharge valve is closed and there is no flow. As the discharge valve opens and the flow increases, efficiency will increase too. It will then decrease again as the flow becomes more turbulent and congested. Somewhere between zero and excessive flow, there is a flow rate that leads to ideal efficiency – the BEP. To be 100% efficient, the kW input should be the same as the water kW output. However, this is never the case due to normal causes of energy losses such as friction and leakages. Consequently, a 75% efficiency rate is considered optimal, while 50% or lower indicates a potential issue. Vibration analysis Pumps produce vibrations that appear at specific frequencies across a wide spectrum. Spectral analysis examines these frequencies to identify problems such as misalignment and imbalance, flow pulsation, bent or damaged shafts, bearing failures and cavitation. A vibration reading of 1-2mm/s is generally considered to be healthy. Based on the type of pump, the application and the medium being pumped, a technician can advise on the proper course of action when vibration exceeds this threshold level. Because of the many variables to consider, pump owners who opt to have a vibration sensor installed should discuss with an expert what a heathy vibration range should look like for their system, and not be tempted to simply increase the threshold when the sensors flag up an issue. In critical equipment such as industrial pumps, seemingly minor issues can quickly turn into major headaches. By taking a preventive approach to pump maintenance, pump owners can ensure that their operations keep flowing. n Seemingly minor issues from worn bearings to damaged seals can lead to entire pump systems being shut down. Preventive maintenance can help identify potential threats before disaster strikes. Brian Tait, head of pump services at Houghton International, explains.