Pump failure can result in costly downtime, repair and damage. Understanding the causes of failure can help in the selection of the pumping equipment to reduce the chances of it occurring. Here, we look at four common causes of pump failure and how to avoid them.
Cavitation is the result of insufficient pressure at the suction end of the pump or Net Positive Suction Head Available (NPSHa) causing the liquid in a pump to turn into vapour at low pressure.
At low pressures, this creates air bubbles which implode as the liquid moves from the suction side of the impeller to the delivery side.
The air bubble implosion generates a shockwave that stresses the pumps’ internal surfaces, creating vibration and mechanical damage, and can ultimately result in failure.
When this occurs repeatedly, cavitation can cause pitting and fractures in the impeller, volutes and casing, weakening the metal, increasing resistance to flow and reducing pumping efficiency. The shock loads from cavitation can also decrease the service life of the shaft and motor.
Cavitation and the related problems it causes can greatly impact the life of a pump, reducing it by 10-15 years, or even more in extreme cases.
Cavitation is most easily avoided during the design stage, ensuring the chosen pump will have sufficient NPSHa so that the liquid remains above vapour pressure.
The NPSH will need to be calculated for each application as vapour pressure is different for different liquids and varies with pressure and temperature.
This can then be used when selecting a pump as manufacturers will be able to provide the Net Positive Suction Head Required (NPSHr) for any of their pumps to match it with the specifications.
Corrosion in pumps is the result of a chemical reaction between the metal and the fluid being pumped.
This reaction can cause uniform corrosion of the wet surfaces – found mostly in pumps made from non-stainless steel materials – or localised corrosion of a small portion of the components – occurring most commonly where metals that form oxide layers that adhere to and passivate the surface.
When corrosion does occur, pump performance and efficiency can be affected, increasing the need for more frequent maintenance and more downtime, and if left untreated it can lead to failure.
The key to mitigating corrosion is by selecting a pump manufactured from the most appropriate materials for the application.
Cast iron is amongst the cheapest options for pump materials and is often used for casings.
It has good corrosion resistance to neutral and high pH liquids, making it a popular choice for general purpose, irrigation and mining pumps. However, it is not suitable for low pH applications where it is more prone to corrosion.
Stainless steel is one of the most commonly used materials for pumps as it has good corrosion resistance in a wide range of environments where other carbon and low alloy steels would corrode.
Under some circumstances, such as exposure to aqueous environments where chloride is present, pitting corrosion may occur on lower grades of stainless steel.
However, this is not an issue for higher grades of stainless steel, which have a high level of corrosion resistance.
Therefore, corrosion is most easily avoided when selecting a pump.
Material selection will determine corrosion resistance in a particular application as well as the pump’s overall cost, including initial cost, maintenance, replacement, downtime, lifecycle and reliability.
Fouling occurs when particulate matter adheres to a pump’s internal surfaces, most commonly in the distribution lines connected to the intake or outflow.
When this occurs, pumping efficiency and flow capacity are decreased, and may eventually lead to failure.This is an unavoidable problem, but is more prevalent in applications where the fluid being pumped contains particles.
However, various cleaning methods can be used to maintain the pump and improve efficiency and capacity.
Wear is inevitable when running a pump, however, there are a few factors that can cause excessive wear, speeding up deterioration of the pump.
Particulate matter in the pumped fluid can lead not only to fouling but also increases the pace of wear on a pump.
These particulates scour a pump’s interior surfaces and roughens them, reducing pumping efficiency over time as it needs to work harder to move the fluid.
Eventually, the pump will become so worn that it will be unable to produce enough lift and may cause excessive vibration.
Wear can also be the result of an improperly sized pump which can cause an imbalance of pressure, putting undue stress on the bearings and seals; turbulence; fluid velocity; deterioration of wear rings; and erosion and corrosion.
Wear rate can be slowed down by ensuring the pump size and materials are suitable for the application, and regular maintenance is carried out to find and fix any problems before they result in unexpected downtime or pump failure.
Going to the experts for help
Malcolm Eyre, Managing Director at Franklin Electric, said it is important to talk to a manufacturer if you’re unsure what pump will be best for your requirements, or if you’re having problems with your current pumps.
“As a manufacturer, we place a high value on providing our customers with the best and most reliable solution for their application; finding a pump that not only matches the needs of the client, but also their budget, no matter if they’re looking at short or long-term cost savings.
“As we are based in Australia with both regional and metro teams, we are able to send one of our experienced engineers to assess your application for the right pump, or to help you troubleshoot any issues you might be having with your current Franklin Electric pump(s) or undertake any required maintenance.
“Pumps will inevitably need maintenance at some point and having access to a pump engineer that can come direct to you to get your pump working optimally again is important.
The manufacturer is best placed to undertake this maintenance, and evaluate and troubleshoot any problems you might be having as they will know what the best solution will be for that pump.”
This partner content is brought to you by Franklin Electric. For more information, visit franklin-electric.com.au.