Upgrading what used to be a small workshop into an industrial-grade factory is a step many small manufacturing businesses eventually take, but as you get the machinery together and look at what you'll need to move from small-scale to big-time factory work, you're going to hit contradicting terms and needs that could make or -- literally -- break the rest of your equipment. Among these contradictions are the air pump and the air compressor. If you've heard from someone that you should really get an air compressor for a particular mechanical setup, be sure that's actually what you need, and not really an air pump.
Are You Moving the Air, or Is the Air Moving a Part?
Compressors do what the name says: They compress gases like air while moving that air forward to other parts of a machine. The compression increases pressure, and that pressure allows the gas to start moving other parts. This is the concept behind equipment like pneumatic drills.
Air pumps just move the gas along. If all you're doing is forcing air into another part of the equipment, with no other intended effect than the air is now somewhere else, you need an air pump, not a compressor. If you need to power equipment (or move parts) with the air that you're moving, then you'd want to look into compressors.
Will Liquid Ever Flow Through the Device?
Given that you're looking for something specifically called an air compressor or pump, asking about liquid moving through it seems strange. But if the part will eventually be used to move not only air but also, say, water, you need a pump, not a compressor. Compressors work with gases only. If that equipment will eventually have liquids involved, you need a pump.
Is This Something That Needs to Be Carried?
Are you getting a portable piece of equipment that is supposed to be carried in a backpack-type container? Then you'd most likely be looking at a compressor. There are portable air pumps, of course, but if the one you were thinking of was a backpack that a worker would carry around, that is most likely a compressor and not an air pump.
Eventually you'll get your larger factory into shape and continue to automate and expand as needed. During this initial expansion, it's normal to encounter issues that aren't quite clear because you're making such a big leap in terms of what machinery you need. But this confusion should settle down as you gain more experience running a bigger operation. Contact an installer, like Compressed Air Systems, for more help.