There is an ambiguity in the use of the term pump, since it is generally used to refer to fluid machines that transfer energy, or pump incompressible fluids, and therefore do not alter the density of their working fluid, unlike other machines such as compressors, whose field of application is pneumatics and not hydraulics. But it is also common to find the term pump to refer to machines that pump other types of fluids, just as vacuum pumps or air pumps are.
The main classification of the pumps is established according to the operating system on which they are based.
Volumetric pumps, in which their operating principle is based on hydrostatics, so that the pressure increase is made by the thrust of the walls of the chambers that vary their volume. In this type of pump, in each cycle the propulsion organ generates a given volume or cylinder capacity in a positive way.
If the maximum volume of the displacement can be varied, we speak of variable volume pumps. If that volume cannot be varied, then the pump is said to be of fixed volume. This type of pump can also be subdivided into
Alternative plunger pumps, in which there are one or more fixed compartments, but the volume is variable, by the action of a plunger or a diaphragm. In these machines, the movement of the fluid is discontinuous and the loading and unloading processes are carried out by valves that open and close alternately. Some examples of this type of pump are the reciprocating piston pump, the rotary piston pump or the axial piston pump.
Rotary or rotary-static volumetric pumps, in which a fluid mass is confined in one or more compartments that move from the inlet area (low pressure) to the outlet area (high pressure) of the machine. Examples of this type of machine are the vane pump, the lobe pump, the gear pump, the screw pump or the peristaltic pump.
Rotodynamic pumps, in which the operating principle is based on the exchange of the amount of movement between the machine and the fluid, applying hydrodynamics. In this type of pump there are one or more impellers with blades that rotate generating a pressure field in the fluid. In this type of machine the flow of the fluid is continuous. These hydraulic generating turbomachines can be subdivided into:
Radial or centrifugal, when the movement of the fluid follows a path perpendicular to the impeller axis.
Axial, when the fluid passes through the channels of the blades following a path contained in a cylinder.
Diagonals or helicocentrifuges when the fluid path is in another direction between the above, i.e. in a cone coaxial to the impeller shaft.
Electric pumps. Generically, they are those driven by an electric motor, to distinguish them from motor-pumps, usually driven by internal combustion engines.
Pneumatic pumps which are positive displacement pumps in which the input energy is pneumatic, normally from compressed air.
Hydraulically driven pumps, such as the ram pump or the waterwheel.
Manual pumps. A type of hand pump such as the rocker pump.
Diesel powered pumps. A type of pump powered by a diesel engine.
In a “suction pump”, a cylinder containing a movable piston is connected to the water supply by a tube. A valve blocks the inlet of the tube into the cylinder. The valve is like a hinged door, which only opens upwards, letting the water rise, but not fall. Inside the piston, there is a second valve that works in the same way. When the crank is operated, the piston rises. This increases the volume underneath the piston, and therefore the pressure decreases. The normal air pressure acting on the surface of the water, from the well, makes the liquid rise up the tube, crossing the valve -which opens- and makes it enter the cylinder. When the piston drops, the first valve closes, and the second valve opens, allowing the water to pass to the top of the piston and occupy the cylinder above it. The next upward stroke brings the water up to the spigot and, at the same time, gets more water into the cylinder below the piston. The action continues as the piston rises and falls.
A suction pump is limited in its action in certain respects. It cannot provide a continuous stream of liquid or bring the water up more than 10 m. between the well surface and the lower valve, as normal air pressure can only act with sufficient force to maintain a water column of that height. A booster pump overcomes these obstacles.
The impeller pump consists of a cylinder, a piston and a pipe that goes down to the water tank. It also has a valve that lets water into the cylinder, but not back out. There is no valve on the piston, which is completely solid. From the bottom end of the cylinder, a second tube comes out that goes into an air chamber. The entrance to that chamber is blocked by a valve that lets water in, but not out. From the lower end of the air chamber, another pipe carries the water to a roof tank or a hose.