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positive pump : is used in high pressure (P) and can be fixed displacement or variable pump with oil
centrifugal pump : is fixed displacement but used in high ( H ) with water
POSITIVE PUMP will only displace certain amount of liquid (depending on element size). The pressure will increase as a result of liquid accumulation in the system. A check valve and safety valve is mandatory on discharge of this pump type. Piston, vane, screw and gear pump are most common used in this category
CENTRIFUGAL PUMP will increase pressure of liquid on 2 stages
Stage 1: increase kinetic energy of the liquid by direct exposure to rotor impellers
stage 2: Convert kinetic energy to static pressure by forcing liquid to move through diffuser or volute at impeller tip (Discharge). The flow will enter impeller in axial direction (Impeller eye) and will be discharged in radial direction. In case of multi-stage pump, return channels are used to redirect flow from radial direction of previous impeller to axial inlet of the next impeller
Centrifugal pumps use a rotating impeller to create a vacuum in order to move fluid. The pump’s impeller rotates within the housing and reduces pressure at the inlet. This motion then drives fluid to the outside of the pump’s housing, which increases the pressure enough to send it out the discharge.
A positive displacement pump forces a predetermined fluid quantity from the pump inlet to the pump discharge for each pump cycle