Cavitation is the most common cause of inexplicably short service lives. It announces itself audibly long before visible damage occurs – anyone who knows the sound can intervene early and avoid expensive consequential damage to valves, plungers and seals.
The cause almost always lies on the suction side. How an inlet must be designed so that cavitation does not arise in the first place is described in installation and system design.
What is cavitation?
Cavitation occurs when the pumping chamber does not fill completely during the suction stroke. In the resulting partial vacuum, part of the water vaporises – one litre of water becomes roughly 1,600 litres of vapour. On the pressure stroke these vapour bubbles collapse back into liquid abruptly, and the resulting implosions damage valves, valve seats and plunger surfaces.
How do I recognise cavitation?
Typical signs are a rough, knocking or grinding running noise, fluctuating pressure and increased pulsation. On inspection, pitting appears on valves, valve seats and plungers. Cavitation damage subsequently destroys the seals as well.
How do I prevent cavitation?
Three factors are decisive. First, fluid temperature: observe the temperature limits in the data sheet and pressurise the inlet with hot water. Second, speed: never exceed the rated speed and, when in doubt, run slower. Third, inlet pressure: provide an adequate, generously sized inlet line, keep the run short, keep filters clean and, where needed, add a booster pump or inlet stabiliser. Important: inlet pressure under flowing conditions is always lower than at standstill.