From Working Guide to Process Equipment, Third Edition

The single most common operational problem in a process plant is loss of suction pressure to a centrifugal pump. If the suction pressure is too low, the discharge pressure and the discharge flow become erratically low. The suction pressure, while low, remains comparatively steady.

31.1 Cavitation and Net Positive Suction Head

The problem described above is called cavitation. A pump that is operating in a cavitation mode may also (but often does not) produce a sound similar to shaking a bucket full of nuts and bolts. A cavitating motor-driven pump always draws an erratically low-amperage flow. This is consistent with the erratically low flow rate.

(Caution: When a pump completely loses flow, it runs smooth, steady, and quiet. Its discharge pressure is stable. Its discharge flow is also stable and steady a steady zero. This is not cavitation. The pump impeller is just spinning, to no particular purpose, in the empty impeller case.)

31.1.1 Causes of Cavitation

Let us assume liquid flows from an 8-in line into the suction of a centrifugal pump. The liquid enters the pump s impeller through a circular opening, called the eye of the impeller, in the center of the impeller. Let us assume that this eye has a diameter of 2 in.

The velocity of the liquid increases by a factor of 16 (i.e., 8 in 2 in, squared). The kinetic energy of the liquid increases by a factor of 264 (i.e., 16 squared) But where does this large increase in kinetic energy...

Products & Services
Centrifugal Pumps
Centrifugal pumps consist of a set of rotating vanes, enclosed within a housing or casing, that are used to impart energy to a fluid through centrifugal force.
Axial Flow Pumps
Axial flow pumps or propeller pumps allow fluid to enter the impeller axially. They discharge fluid nearly axially, pumping the liquid in a direction that is parallel to the pump shaft.
Liquid Handling Pumps
Industrial liquid handling pumps are classified in many different ways, and are distinguished by the media pumped and the fluid motive mechanism (dynamic or displacement).
Turbine Pumps
Turbine pumps are centrifugal pumps that use pressure in combination with a rotary mechanism to transfer fluid.  They typically employ blade geometry, which causes fluid circulation around the vanes to add pressure from inlet to outlet. 
Condensate Pumps
Condensate pumps are used to collect and transport condensate back into a steam system for reheating and reuse, or to remove unwanted condensate from an HVAC or appliance collection pan.

Topics of Interest

Overview I am an anticommunist. That was not always so. But working in the former Soviet Socialist Republic of Lithuania altered my views about communism. Figure 32.1, drawn to scale, illustrates the...

Pump reliability problems can be responsible for a large amount of the maintenance budget and lost-opportunity cost at chemical process plants. Typical reasons for pump failures can be diagnosed...

Today, two main types of pump dominate the scene in the chemical process industries: positivedisplacement pumps and impeller pumps. For pumping applications that involve highly volatile fluids, the...

The importance of adequate fluid pressure at the suction side of a centrifugal pump is well known, as is the complication posed by dissolved gas in the process fluid. Less widely known are some of the...

Net Positive Suction Head where W = weight rate of flow, lb/h TDH = required total dynamic head of the pump, ft P 1 = pressure in suction vessel, psia P 2 = pressure in discharge vessel, psia ?...