OK, so how does priming work? Very cleverly actually.

There is a kind of 'service station' where the print head is positioned for priming. When in position, a rubber cup seals against the face of the print head and connects with a drain tube below. In the base of the printer is a positive displacement roller and tube pump - a set of rollers (I assume they are rollers as I did not entirely disassemble the unit) rotates against a compliant plastic tube (like the blood pump in a heart-lung or dialysis machine if you have ever seen one of those). The direction of flow is determined by the direction of rotation of the rollers. This is controlled by the position of a spring loaded 'feeler' which enables one of three 'shift levers' to be lifted to engage the sucking pump (Maybe, one of them blows - I didn't entirely figure out what they all did). The position of the 'feeler' is determined by print head location which is under control of the print head servo system. Thus no additional electronics is needed. Slick. The priming action, which ...  more