A small air compressor for cleaning?
There are very small tank type units, but around 1gal is the smallest that seems to be available. 

Here is one that is really small and quite reasonable, and from a reputable company.

You can gauge the size by the relationship of the typical pressure switch to the rest of the unit.

http://www.amazon.com/Senco-PC1010-1-Horsepower-1-Gallon-Compressor/dp/B0000AQK78