A paint spraying system having a paint reservoir (16) remote from a spray gun (12) of the type which draws paint to the gun using vacuum (6, 7). A paint pump (14) delivers paint under positive pressure to the paint gun and a paint regulator (28) in or associated with the paint gun delivers the paint to the gun as drawn by vacuum by the gun through the regulator. An over-pressure relief valve (70) may be used to limit the positive pressure delivered by the pump. A mechanical switch may be used to select a SPRAY or CLEAN mode for the operation of the paint regulator to allow flushing of the paint regulator.