Pumps

A pump is a mechanical device used to move liquids or gases. Also the heart is an essential pump in humans and animals to move the blood around.

The earliest pump was described by Archimedes around 300 BC and is known as the Archimedes screw pump. Pumps work by using mechanical forces to push the material, either by physically lifting, or by the force of compression.

Types of pumps

Pumps fall into two categories: positive displacement pumps, which force fluid from one sealed chamber to another with little leakage, and dynamic pumps, which use the momentum of the fluid to move it across an unsealed chamber.

Positive displacement pump

This type of pump forces the fluid from one chamber to another by reducing the volume of the first chamber while increasing the volume of the second. Such a pump produces a constant flow regardless of intake pressure or outlet pressure, unless the intake pressure drops below a certain limit, causing cavitation, or the outlet pressure exceeds the capacity of the pump, causing pump failure. These pumps often have a relief valve to prevent the latter problem.

Reciprocating positive displacement pump

Hydraulic ram
Nodding donkey
Stirrup pump
Vane pumps (with flexible or rigid vanes)
Piston pumps
Diaphragm pump

Rotary positive displacement pump

Screw (or progressing cavity) pump
Gear pumps (internal and external)
Lobe pumps
Peristaltic pump (uses a process similar to peristalsis in animals)
Circumferential piston pump
progressive cavity pump : pumps fluid by the rotation of a helical steel rotor inside a rubber pump body with a helical aperture

Dynamic pump

The dynamic pump causes the fluid to move from inlet to outlet under its own momentum. This type tends not to need a release valve, because as the outlet pressure rises the pump simply becomes less efficient. Fluid motion can be rotary, as in centrifugal pumps, or linear, as in reciprocating dynamic pumps.

Rotary dynamic (centrifugal) pump This type of pump contains a rotating part called the impeller inside a stationary cavity called the volute. The impeller forces the fluid to rotate, and thereby to move from inlet to outlet under its own momentum. Examples:

turbopump: the fluid is moved by the blades of a high-speed turbine.
submersible pump : the fluid is moved by a pump joined to a sealed motor and submerged in the fluid to be pumped.
split case centrifugal pump : the fluid is pumped by a horizontal or vertical pump with a split volute to allow maintenance access.
axial flow pump : the fluid is pumped by a propellor type impeller inside a section of pipe.

Linear or reciprocating dynamic pump

The Vortec Transvector is one example of a no-moving-parts dynamic air pump. A film of fast moving air formed by releasing high pressure air through a slit is discharged adjacent a surface, and drags ambient air along with it. The higher the pressure of the primary air supply, the worse the performance.

It is an example of an ejector pump. Steam ejectors are used to cool bleach water so it will retain the chlorine. They simply discharge a boiler into a tube, sucking water vapor out from above a sealed tank. The water inside slowly cools. Not very efficient, but does something useful with waste steam, simply.

A well pump is also a dynamic pump. Since water will boil if any attempt is made to "suck" it more than about thirty feet high, high pressure water is injected in at the bottom of a well, forcing the well water to flow upwards much more than thirty feet.

Ejectors are used to augment the flow in turbojets, near the aft end.

The Coanda effect is the tendency of such a moving stream to cling to a surface, even when the surface deflects the stream away from its original direction. The surface seems to pull the stream. It's a manifestation of Bernoulli's law: since energy is conserved, a moving fluid has a lower pressure than a static fluid.

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