Centrifugal pumps
Most centrifugal pumps will not last very long if not operated within its design parameters. The most common problems are usually associated with inadequate suction head or excessive discharge head:
Cavitation is the term used to describe the formation of voids at the center of a pump (the area of lowest pressure) and subsequent collapse as the voids move outward in the pump (area of higher pressure). In larger pumps it actually sounds like rocks tumbling around in the pump. It is most commonly caused by insufficient suction head.
Vortexing is the term used to describe when a pump creates a whirlpool and entrains air into the pump suction. Vortexing is also noisy, but you should notice the air bubbles in the pump discharge. The pumps used for air induction protein skimmers are designed to entrain air, usually through an air line. Vortexing is also commonly caused by insufficient suction head.
There are two ways to correct both cavitation and vortexing:
Increase suction head by lowering the pump or raising the water level above the pump.
Decrease flow by throttling the pump to reduce the suction head required.
Prior to starting a pump that has been out of the system it should be vented, some pumps are self priming by design but most are not. The majority of air should be allowed to escape prior to starting the pump.
Although most pumps can be throttled to flow rates much lower than design, prolonged operation at shutoff head (deadheading) should be avoided. Every pump adds a small amount of heat to the water due to friction, and completely blocking the flow can cause a pump to overheat.
Pneumatic and electric diaphragm pumps
2012-09-14
