A new white paper from Xylem reports that cavitation damage to pumps is increasing, very often due to poor system design and cost pressures during the design process. “Pump cavitation and how to avoid it” highlights cavitation issues, and in particular the need for prevention measures at the design stage.
“We have seen a significant increase in cavitation issues in the last five years, primarily due to poor pump system design and a lack of awareness about how cavitation is caused,” says Bob Went, an expert in pump system design at Xylem who wrote the white paper.
“Engineers in the water industry are now expected to deal with a very wide range of different technologies, and it is therefore impractical for them to be expert in all areas such as system design and cavitation problems,” says Went. “The result is that cavitation related problems are on the increase despite the fact that it is an age-old phenomenon.”
Cavitation is caused when liquid in the pump turns to vapor bubbles at low pressure. The bubbles then implode, which creates a shockwave that hits the impeller creating pump vibration and mechanical damage that ultimately leads to pump failure.
“I am personally aware of an increase in the number of installations where pump problems caused by cavitation, such as vibration, are severe and may lead to mechanical damage to the pump. Cavitation related problems also have the potential to reduce pump life from circa 10-15 years down to just two years in some cases.”
Went says that all too often the pump itself is blamed. “Pumping system problems, which can be many and varied including cavitation, often manifest themselves at the pump but are rarely caused by it. In fact, nine out of ten pump problems are not caused by the pump itself but by issues such as cavitation, poor system design, lack of maintenance, etc.”
He continues: “Good system design is critical. Cavitation is simple to avoid at the design stage, but in the field, once operational, it can be very difficult and expensive to put right. There has been an increase in the number of projects where a new pump is put into an existing installation with insufficient attention being given to avoid cavitation problems. This is best achieved by ensuring sufficient suction pressure is available.
“Rather than make some simple design alterations, such as using larger diameter pipes or removing concrete to place the pump at a lower level, cost pressures can sometimes drive engineers to make the wrong decisions, which ultimately reduce the life of the pump.”
He concludes: “My advice to pump users is to get pump experts in at the design stage. There are a range of options available to avoid cavitation issues, but it must be dealt with at the outset rather than as a rectification issue. A little extra cost at the design stage will save a lot of hard work and even more investment to put it right later.”