Ink jet printhead

A drop-on-demand inkjet printhead comprising an array of ink jet orifices (5 Fig 3) in a block (83) mounted at the front of an ink reservoir 3 so that when the printhead is 'pointing' horizontally or vertically downwards there is a hydrostatic head of ink producing a positive pressure at the orifices such as to cause weeping of the ink from the orifices between printing operations. The invention provides air valves A, B within the reservoir 3 arranged so that one of them always provides a port (41, 43 Fig 1) above the ink level. A pump 105 and valve arrangement 101-104 maintains a vacuum or positive pressure in the reservoir 3 such as to produce a slight negative pressure at the orifices (5). Other features of the printhead are disclosed in the spec.