Further to the previous TECHMAIL on Design of Pumping Systems, here are a
few web-based articles concerning pump cavitation (all are linked at
<a href="http://www.PipingDesign.com/pumps.html">http://www.PipingDesign.com/pumps.html</a>):
Understanding Pump Cavitation
[Osmonics.com]
Cavitation is a major problem in the chemical industry because it affects a basic tool, the centrifugal pump. A sudden increase in the velocity of the pumped liquid reduces the inlet pressure, sometimes below the vapor pressure.The result is formation of gas and bubbles.
Detecting the signs of cavitation, and correctly identifying and understanding the type of cavitation present, can help an operator prevent serious damage.
HOW CAVITATION OCCURS The pressure of the liquid in a centrifugal pump drops as it flows from the suction flange through the suction nozzle and into the impeller (Fig. 1). The amount of pressure drop is a function of many factors, including pump geometry, rotational speed, frictional and hydraulic shock losses, and flowrate.
See <http://www.osmonics.com/products/Page785.htm> for the continuation of this article and explanatory graphics.
What is Cavitation?
[Pump-Zone.com]
Cavitation is the formation of partial vacuums in a flowing liquid as a result of the separation of its parts. There are two types of cavitation. Suction side cavitation is by far the most common form (probably 90% of all known events). Discharge cavitation is significantly less common (occurs 10% of the time).
Suction side cavitation is a restriction on the suction side of the pump system which does not allow sufficient fluid to enter the pump and to be discharged. The pump reacts to pressure on the discharge side and produces a higher flow of liquid than can be drawn in on the suction side. Restrictions either on the suction side of the pump or atmospheric pressure decreases the flow to the pump, particularly in suction lift applications. The pump produces a higher flow of liquid than can be supplied to it, due to suction side restrictions.
Discharge side cavitation is a restriction on the discharge side of the pump system which constricts the fluid flow out of the pump. Since liquid can't escape due to discharge side restrictions, it is recirculated in the pump casing, damaging the outer edge of the impeller and casing, or the casing ring if present.
See <http://www.pump-zone.com/articles/articles/nutshell.htm> for the full article.
PUMP INTAKES
[Richard Neff]
PART 1 - Designing Intake Lines
PART 2 - Installing Intake Lines
PART 3 - Diagnosing & Repairing Intake Lines
PART 4 - Pump Cavitation In Depth
The complete article is at <http://fisstate.org/pumpint.htm>, along with photographs.
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