“Can it replenish itself?”

Automatic pistols

Automatic pistols use cartridge ammunition in magazines. Typical cartridges, or rounds, comprise the bullet, the propellant, a primer and a casing that holds the round together. With each shot, the primer is struck igniting the propellant which expands, propelling the bullet from the gun’s barrel. The remaining energy of the propellant is used to discard the spent casing and recover a new round from the magazine.

String trimmer

A string trimmer is used in tight areas, like along a fence line, spinning the string to cut the grass. Because the string often encounters hard obstacles it tends to wear and break off. Most string trimmers have a mechanism to spool out string in a measured way so that the length of string is recovered.


Toilets use a reservoir of water which is discarded to chase waste down the drain. Each flush involves lifting a small flap which holds the reservoir water back from flowing into the toilet bowl. The flap is buoyant which causes it to ride the top of the water in the reservoir until the water level is higher than the flap, at which point the flow of water drags the flap closed. The reservoir continues to fill until a float valve reaches the top of its travel, which corresponds with the maximum capacity of the reservoir, at which point the valve closes and the recovery of water is complete.


Principle 34 – Discarding and Recovering is distinct from Principle 27 – Cheap, Short-Lived Objects because the object being considered is not a cheap, short-lived object. Instead, the object being considered is discarding and/or recovering cheap, short-lived objects.

A disposable napkin is an example of Principle 27 at work.  A disposable napkin dispenser is Principle 34 at work.

More examples

As I stumble across real world examples of this Inventive Principle in action I add them here.

Your turn

What problems do you face that this inventive principle could help solve? Have you used this principle before?

Photo https://www.worx.com/20v-gt-trimmer-edger-wg160-3.html