The simple pneumatic dispensing machine is generally low cost and almost ubiquitous. They improve the application of materials like single part adhesives, coatings, sealants and inks, by enhancing a manual process to one which is more controlled and repeatable, while health and safety benefits include less mess, less exposure to potentially hazardous chemicals and fewer RSI issues.
These systems work by filling an industrial syringe or barrel with the liquid material. Pulses of air then push the liquid out of the other end, usually through a dispensing needle or tip. The quantity dispensed can be varied by the size of the needle orifice (from as small as 0.15mm), the pressure applied and the time of the air pulse triggered by footswitch, finger switch or automation. They may be hand-held or mounted on positioning robots or rotary tables.
Less than 1% variance is often easily achievable, and 0.1% not uncommon. Digital timers further improve accuracy.