While severe cavitation is usually accompanied by excessive noise and damage tot he pump, mild cavitation may produce nothing more than a small reduction in pump efficiency and moderate wear of pump parts. For any pump with a given size suction line, capacity or maximum speed is fixed by the existing net positive suction. In fact, most cases of low flow rates can be traced to starved suction conditions due to either too high a static lift, too long a suction line, or a combination of both. Cavitation is harmful to diaphragm life because on the suction stroke the diaphragm is being pulled mechanically by the shaft connected to the pressurized diaphragm. The lower the suction lift condition imposed on the diaphragm, the less the unbalanced mechanical load, and the longer the diaphragm life.
Every diaphragm has a given number of flexes before failure.
Cavitation can be eliminated in air-operated double diaphragm pumps easier than with any other type of pump. Start the pump slowly by controlling the volume of compressed air to the pump by the use of a gate or globe valve. After the unit starts pumping, the throttling valve can be opened to increase capacity. The point at which further opening of the valve increases cycling rate without an increase in discharge rate will be the cavitation point, and the valve should be closed slightly. Under conditions of limited flow due to cavitation, damage to the double diaphragm pump will most likely be limited only to the diaphragms, in comparison to numerous expensive components in other types of pumps.