Airless sprayers provide pressure from either a diphragm or piston pump unit driven by an electric, gasoline, or air power motors. Some models use a hydraulic driven pump powered by electricity or gasoline power. The hose is an integral part of the system. Its expansion and contraction provides volumetric cushioning of the fluid to provide steady paint flow at the tip. It also conducts static electricity build up back to the sprayer where it can be grounded.
Many companies use one pump on a variety of models.
The difference comes from the motor and powertrain with changes in horsepower or motor type. Bigger pumps have bigger valves and bigger valves means more heavier fluids can pass through. For example, a small pump such as the Graco 395ST PRO or SprayTECH 2105 has insufficient horsepower to push elastomeric coatings. As the same pump body is put onto larger motors, its ability to pump more fluid increases because the motor can turn it faster. However, because of faster cycling, you can expect more wear than a larger capacity pump.