Difference between Centrifugal pumps and Positive Displacement pumps

Centrifugal Pump

Centrifugal pumps use a rotary vane impeller to impart kinetic energy by increasing the velocity of the liquid. This high velocity of the liquid will then produce a velocity head and at the same time producing a high flow rate.

Characteristics of Centrifugal Pump:
- higher power costs
- not self-priming
- gives less pressure to the fluids being pumped
- delivers a variable volume of fluid depending on the fluid's discharge pressure
- well suited for high flow conditions
- flow rate of liquid pumped varies depending on the system pressure or pressure head
- flow rate is inversely proportional to the viscosity of the liquid (flow is decreased if the viscosity is increased)
- centrifugal pumps has practical applications in pumping liquids with low viscosity
- run at higher speeds than positive displacement pumps (PD pumps)
- lower tolerance for entrained gases

Types of Centrifugal pumps:
1. Axial Flow - single stage, multistage
2. Radial Flow (Mixed Flow) - single suction, double suction
3. Peripheral Flow - single stage, multi-stage

Uses and Applications of Centrifugal pumps:
- general water supply for buildings
- overhead and pneumatic tank systems
- domestic water supply systems
- dairy farmers
- hot-water circulating service
- shallow wells and in deep wells
- booster fire pumps for fire protection systems
- construction companies
- cooling of engines, automotive factories
- sump, sewage drainage
- can handle abrasive, corrosive, dirty fluids
- hygienic purposes such as food, pharmaceuticals    
- irrigation and agriculture purposes
- chemical, petrochemical, fertilizer plants
- ship's bilge pumping
- cryogenics industry in extreme cold applications
- electric and power generation industries
- beverage, softdrink, soda, pop, distillery corporations
- textile, fabric industries
- pulp, paper industry
- and more...

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Positive Displacement Pump

Positive displacement pumps apply a force (by using a piston, for example) to move a fixed volume of fluid inside the casing of the pump.

Characteristics of Positive Displacement Pump:
- lower power costs
- self-priming
- gives more pressure to the liquid being pumped
- delivers a constant volume of fluid even with varying discharge pressure
- used for low flow applications
- liquid pumped has a relatively constant flow regardless of the system pressure or pressure head
- flow rate is directly proportional to the viscosity of the liquid (flow is increased when viscosity is increased)
- positive displacement pumps are generally used for pumping liquids with high viscosity which in turn provides a higher volumetric efficiency
- creates a vacuum on the suction side of the pump thereby creating a suction lift
- higher tolerance for entrained gases

Types of Positive Displacement Pumps:
1. Reciprocating - piston/plunger, diaphragm
2. Rotary - single rotor, multiple rotor

Uses and applications of Positive Displacement Pumps:
- metering applications
- high viscosity application
- food, chocolate, beverage factories
- hazardous chemicals, slurries and pastes
- pharmaceutical products
- paint, resins, adhesives, glue industries
- fuel booster pumping systems
- lubricating oil systems
- pulp, paper, mill industry
- manufacturing applications
- diesel fuel handling and distribution 
- and more...