Damage caused by clogging can cause a pump’s mechanism to slow down and lead to pump tripping or worse. Xylem’s research has found the true cause of clogging.
Big or small?Clogging in wastewater systems is a common problem for engineers. Objects in wastewater reach the impeller – the rotating mechanism moving the liquid – which then causes a jam, trip or even a motor burnout. There is still the misconception that clogging is caused by big objects in the wastewater stream and the focus is on preventing this from happening. Instead, the real culprits are not the big objects but the tiny ones: the synthetic fibres and threads.
A rule of thumb since 1915A century old rule of thumb is still used in the world of pumps to prevent clogging risks. This rule determines that a pump’s throughlet (the passage containing the impeller) must be equal to or larger than any object that could be flushed down the toilet. The rule is not redundant, it has resulted in designs for relatively good pump practices for a long time. However, research has shown that this rule is not always so accurate in the prevention of clogging situations. “The biggest issue with the throughlet rule is that it focuses on large and hard objects as the main culprits behind clogs and impeller damage,” says Chetan Mistry, Xylem Africa’s Strategy and Marketing Manager. “But a lot of research, including work by Xylem, shows that this idea is misdirected. Hard and heavy solids tend to settle in low-flow parts of pipe systems and rarely reach pumps. They are not the ultimate source of clogging problems.”
Enlarging the throughlet size means the design of the impeller needs to change to be able to operate within the larger area and avoid damage by larger objects moving through. Examples of these designs are single-vane impellers and vortex impellers. However, they are not so efficient and hard on bearings.