I know this is elementary stuff for most of you. But, we all aren't engineers. For those of us who like to disassemble things and scavenge the parts, I thought you might like to know the different kinds of common springs and what they do. I have buckets full of these things and they come in very useful.
This Instructable is open to collaboration. I would like to include "real" examples of these different springs in use. If you have an image, load it up and file it under the particular type of spring. Don't worry if it is incorrect or may fit more than one category. I may go in and rearrange for clarity.
Step 1: Compression Spring
A compression spring squeezes together to create a load. You will often find these inside switches, automotive suspensions, and jacks-in-the-box.
Step 2: Extension Spring
The extension spring stretches apart to create load. They often have little loops on the ends to attach to things. You may find these on the screen door hinge, garage door hinge, and bouncy decorations that hang from the ceiling. The Slinky(tm) is a very weak extension spring.
Step 3: Torsion Spring
The torsion spring rotates around an axis to create load. They release their load in an arc around the axis. They are commonly found in mouse traps and rocker switches. They are good for things that rotate less than 360 degrees.
Step 4: Constant Force Spring 1
Also called a "clock spring", because it is often found in clockworks. This spring is made of a band of steel wrapped around itself a number of times to create a geometric spiral. The idea is to create a rotational force that releases a constant amount of load, instead of a quick burst of power. Besides clocks, they are found in all sorts of wind-up toys. Be careful when removing these from a mechanism. They tend to unravel with a dynamic flair and much excitement. They are great for things that need to rotate many times and still have a reasonable amount of force to apply and release.
Step 5: Constant Force Spring 2
This type of clock spring is used when more power is required. It has many fewer rotations and a much thicker band of steel. They are used in automotive seat recliners (pictured here) and other heavy duty applications.
Remove from mechanism only when load is reduced to zero or it may remove some fingers for you.
Step 6: Belleville Spring (aka Belleville Washer)
Belleville springs are a coned disk spring typically containing a hole in the center for a non-permanent fasteners (bolt et. al.). Bolt pretensioning is a typical use for a Belleville washer.
Belleville springs can be nested (making springs in parallel) making more spring deflection for the same amount of load OR allowing higher loads with the same deflection - depending on their orientation. While useful, nesting Belleville springs can be unstable.
With proper design (selection), Belleville springs can be used for a "snap-acting" mechanism. Likewise, with proper design/selection, the spring can have constant force over a large deflection. This type of design maintains bolt pretension when a dynamic load is present or in situation where thermal expansion/contraction is significant.
Cite: Shigley, Joseph et. al. "Mechanical Engineering Design" 7th International Edition. 2004.
Step 7: Spring Clip
This category includes snap rings and hose clamps. The spring is a portion of a circle and the force is applied radially concentric to the center point of the circle.
Step 8: Natural Spring
This is a helical spring found in nature. It is excellent for strangling tomatoes, supporting cucumbers and displaying your grapes. I hope you have enjoyed this Instructable.