Pumps, Compressors & Fans
Pump cavitation, NPSH, slurry pumps, rotary compressors, aftercoolers, fan balancing, and industrial ventilation.
- Diagnose pump cavitation and apply NPSH requirements
- Maintain compressors and aftercooler systems
- Balance industrial fans and diagnose imbalance
Lesson 1
Pump Types & Cavitation
Centrifugal Pump Cavitation
Cavitation occurs when the pressure in the pump suction drops below the vapor pressure of the liquid, causing vapor bubbles to form and then violently collapse. Cavitation is the most destructive condition for a centrifugal pump.
Pump Types for Special Applications
A centrifugal slurry pump is used for slurries and solids. These pumps feature hardened or rubber-lined wear surfaces, open or semi-open impellers with wide passages, and heavy-duty seals to handle abrasive particles. They are found in mining, dredging, and wastewater applications.
Causes of Cavitation
- Suction lift too high - pump too far above the liquid source
- Suction piping too small - excessive friction loss
- Blocked suction strainer - restricted flow
- Liquid too hot - elevated vapor pressure
- Pump running too fast - flow exceeds suction capacity
Prevention
The key to preventing cavitation is maintaining adequate Net Positive Suction Head (NPSH). The NPSHa (available) must always exceed the NPSHr (required by the pump).
Cavitation Destroys Pumps
Cavitation erodes the impeller surface through micro-jet implosions of collapsing vapor bubbles. Severe cavitation can destroy an impeller in hours to days. If you hear a crackling or gravel-like sound, investigate immediately.
Cavitation occurs when suction pressure drops below vapor pressure. It sounds like gravel in the pump and destroys impellers through pitting. Prevent by ensuring NPSHa exceeds NPSHr. Common causes: high suction lift, small piping, blocked strainers, hot liquid.