centrifugal pum & recipocating pump

Centrifugal pumps move fluid by rotating an impeller inside a housing.

Reciprocating pumps work like an auto engine with pistons that move up and down to move the fluid.

Wiki:"how pumps work" for a much better explaination.

You might have to back up one classification there are two types of pumps, dynamic and positive displacement (p.d). Centrifugal pumps -dynamic (no valves input/output). Recip's p.d. (valves in/out). Many types of dynamic/p.d. pumps. A vane pump is a cross between a dynamic pump and a p.d. but is classed as a p.d. because the inlet and outlet are separated by valve action. A gear pump p.d.. The gears are the valves, no flow when not turning.

Propellers, turbines and squirrel cage fans- dynamics air pumps. Piston compressors and internal combustion engines - p.d. (valves). I've presented some examples of "dynamic and p.d. pumps". The centrifugal and recip's are just sub species of them.

In addition, all p.d. pumps require a pressure relief valve of some sort, be it ex/internal.

Due to their principles of operation.

THE CENTRIFUGAL PUMP.

Centrifugal pumps give energy to a fluid by spinning (rotating) it very fast inside a circular casing. The fluid moves outwards from the centre, towards the casing. An increase in velocity causes a greater flow rate in the discharge area of the pump. The movement of the fluid away from the centre is due to the centrifugal force. The action of the centrifugal pump is one way of increasing the energy in the fluid by whirling it around in circles. As it goes around it pushes out from the centre. This outward force is called centrifugal force.

THE RECIPROCATING PUMP

The reciprocating pump types are:

- diaphragm pump;

- piston pump;

- plunger pump.

The plunger type reciprocating pump is the most basic type of positive displacement pump. It can operate either horizontally or vertically. The plunger moves backwards on the suction stroke, and pulls fluid into the cylinder. On the forward stroke (discharge) the pressure increases on the fluid. The pressure is now greater inside the cylinder than in the suction line, which causes the suction check valve to close. As the pressure increases within the cylinder, it causes the discharge check valve to open. This is because there is a greater pressure in the cylinder than in the discharge line. The fluid is then displaced into the discharge line. outside the cylinder, as well as inside, and only displaces an amount equal to the volume of the piston. They are only sealed where the piston enters the casing.The volume of displaced fluid corresponds to the length of stroke (movement), times the diameter of the piston. This amount is only part of the fluid in the cylinder. Plunger pumps are often used on high pressure work, or when the fluid being pumped could cause other types of pump to stick, or mark the cylinder wall. They can, however, work at low or medium pressures where there is continuous pressure, for a long time with minimum maintenance.

Good answer AM, but this sentence is not clear; "An increase in velocity causes a greater flow rate in the discharge area of the pump" This may just be a problem of language usage.

The flow rate throughout the pump remains the same from suction nozzle to discharge nozzle. The velocity is increased from suction eye to discharge of the impeller. The velocity decreases as the area in the volute increases converting velocity energy into pressure energy. (Increases the static head by lowering the velocity head).