There are three basic types of pumps that are relevant to us: the positive displacement, centrifugal, and jet pumps. Within each category there are several different pumps that will be discussed below. The basic concept of the positive displacement pumps is that they create some sort of cavity using pressure to pull the substance into the cavity and then force it out. Centrifugal pumps apply a centrifugal force to push fluids through the system. Jet pumps force the substance through a nozzle in order to create velocity.
==== Positive Displacement Pumps ====
=== Gear Pumps ===
== Internal Gear Pump (Gerotor) ==
A Gerotor has an inner gear within the outer gear.  The inner gear has one less tooth than the outer gear and as they rotate the gears, which interlock form a vacuum or suction-type environment and pull the liquid at a constant rate from one end to the other.((Parker Hannifin Corp. "About Gerotors." 2008. 6 February 2011 <http://www.gerotor.net/about_gerotors.asp>.))\\
To see an animation of this process see: http://www.pumpschool.com/principles/ig_ani.htm OR: http://upload.wikimedia.org/wikipedia/commons/4/4b/Internal_gear_pump.gif

^     Pros     ^     Cons     ^
|High Speed((Pump School. "Internal Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/internal.htm>.))|Pressure Limitations((Pump School. "Internal Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/internal.htm>.)):\\ Can carry about 1-340 m<sup>3</sup>/hr((Hydraulic Institute. "About Pumps." 6 February 2011 <http://www.pumps.org/content_detail_pumps.aspx?id=1772>.))\\ Up to 16 bar pressure((Hydraulic Institute. "About Pumps." 6 February 2011 <http://www.pumps.org/content_detail_pumps.aspx?id=1772>.))|
|Few moving parts((Pump School. "Internal Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/internal.htm>.))| :::|
|Constant and Even Discharge((Pump School. "Internal Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/internal.htm>.))|:::|
|Quiet((Pump School. "Internal Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/internal.htm>.))|:::|
== External Gear Pumps ==
The external gear pumps work the same way as the internal gear pumps, except they use two gears of the same size next to each other to form the suction.((Pump School. "External Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/external.htm>.))\\
To see an animation of this process see: http://www.pumpschool.com/principles/eg_ani.htm

^     Pros     ^     Cons     ^
|Reliable & Accurate Measurements((Pump School. "External Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/external.htm>.))| Cannot handle high temperatures((Pump School. "External Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/external.htm>.))|
|High Pressures (above 200 bar)((Pump School. "External Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/external.htm>.))|:::|
|High Speed((Pump School. "External Gear Pumps." 2007. 6 February 2011 <http://www.pumpschool.com/principles/external.htm>.))|:::|

== Diaphragm Pumps ==
Diaphragm pumps are positive displacement pumps that uses a moving diaphragm to change pressure in a chamber that will receive and then expel the liquid((Haravard Apparatus. "Diaphragm Pumps." 8 February 2011 <http://www.harvardapparatus.com/webapp/wcs/stores/servlet/haisku1_10001_11051_43569_-1_HAI_ProductDetail_N_37295>.)) as can be seen in the following animation: [[http://upload.wikimedia.org/wikipedia/commons/c/c5/Membraanpomp.svg]].\\
A major advantage of diaphragm pumps is that they do not wear out quickly as they have very few movable parts that rub against one another. In addition, they are effective pumps that work just with air.((Haravard Apparatus. "Diaphragm Pumps." 8 February 2011 <http://www.harvardapparatus.com/webapp/wcs/stores/servlet/haisku1_10001_11051_43569_-1_HAI_ProductDetail_N_37295>.))
=== Centrifugal Pumps ===
"The process liquid enters the suction nozzle and then into eye (center) of a 
revolving device known as an impeller.  When the impeller rotates, it spins the liquid 
sitting in the cavities between the vanes outward and provides centrifugal acceleration. 
As liquid leaves the eye of the impeller a low-pressure area is created causing more liquid to 
flow toward the inlet.  Because the impeller blades are curved, the fluid is pushed in a 
tangential and radial direction by the centrifugal force.  This force acting inside the pump 
is the same  one that keeps water inside a bucket that is rotating at the end of a string."((Engineers' Resource. "Centrifugal Pumps: Basic Concepts of Operation, Maintenance, and Troubleshooting." 8 February 2011 <http://www.maintenanceworld.com/Articles/engresource/centrifugalpumps.pdf>.))\\
An advantage of the Centrifugal Pumps is that, unlike the displacement pumps, it flows continuously rather than filling and emptying the cavity as described above.
An image of this system can be seen at: [[http://media.web.britannica.com/eb-media/58/3658-004-061948E8.gif]].\\
For more details and equations regarding Centrifugal Pumps see pages 2-6 in [[http://media.web.britannica.com/eb-media/58/3658-004-061948E8.gif]].

Within this category there are three types of centrifugal pumps. The radial flow pumps is what is portrayed in the picture above in which the water flowing in leaves the system at a 90 degree angle. The axial flow enters and leaves at the same angle. And the mixed flow is a compromise of the two.\\
The Axial Flow Pump therefore operates at higher flow rates, but lower pressures than the Radial Flow Pump.
=== Random Pumps ===
The syringe pump is designed to deliver accurate amounts, but is usually only for small amounts of medication.((Barbara Christe, __Introduction to Biomedical Instrumentation__ (Cambridge University Press, 2009) 209.))