I am seeing quite a few recently purchased, used pumps coming in. There are a lot of used pumps on the market these days, due to the downturn in the painting industry. Most of these pumps haven’t been run for years. Some were broken when they were stored and some were in working order. Remember that storing a pump is the same as storing a car. Taken out of storage, both will need work.
Take the car, for example. If it wasn’t stored properly, you will need a battery, air in tires as a minimum as rubber stored under weight breaks down, so maybe all 4 tires. If the engine wasn’t stored dry, you will need to drain, clean and/or rebuild the fuel delivery system and completely drain, flush and refill the engine oil and cooling systems.
An airless is quite the same. At a minimum; figure filters, screens and a complete repack of the fluid section. If it wasn’t stored properly, then you may need a piston rod and/or sleeve. If it had any residue of paint or colored water in it, the prime valve may not open or close off completely. And if it is a gas powered pump, you will have the additional oil and fuel systems to deal with.
Remember, just because a pump runs, that doesn’t mean that it will pump or pressurize paint.
