A spray head assembly for attachment to a liquid spray gun platform, wherein the spray head assembly comprises: a barrel adaptor configured for attachment to a liquid spray gun platform, wherein the barrel adaptor comprises a nozzle port; an integrated air cap/nozzle removably attached to the barrel adaptor, wherein the integrated air cap/nozzle comprises: a front wall comprising a center air outlet; a nozzle body attached to the integrated air cap/nozzle, the nozzle body comprising an inlet end and a nozzle outlet end; a liquid nozzle opening formed in the nozzle outlet end of the nozzle body; a nozzle body inlet formed in the nozzle body; a nozzle passage extending through the nozzle body from the nozzle body inlet to the liquid nozzle opening; wherein the nozzle body inlet is positioned over the nozzle port on the barrel when the integrated air cap/nozzle is attached to the barrel adaptor such that liquid entering the nozzle passage through the nozzle port exits from the nozzle passage through the liquid nozzle opening; wherein, when attached to the barrel adaptor, the integrated air cap/nozzle defines a center air chamber that extends from the barrel plate to the center air outlet in the integrated air cap/nozzle, wherein air enters the center air chamber through the center air aperture in the barrel plate before passing out of the center air outlet during use of the spray head assembly; wherein removal of the integrated air cap/nozzle from the barrel adaptor removes the nozzle body from the nozzle port of the barrel adaptor, and the nozzle body is configured to be remaining attached to the body of the integrated air cap/nozzle. a barrel adaptor configured for attachment to a liquid spray gun platform, wherein the barrel adaptor comprises a nozzle port; an integrated air cap/nozzle removably attached to the barrel adaptor, wherein the integrated air cap/nozzle comprises: a front wall comprising a center air outlet; a nozzle body attached to the integrated air cap/nozzle, the nozzle body comprising an inlet end and a nozzle outlet end; a liquid nozzle opening formed in the nozzle outlet end of the nozzle body; a nozzle body inlet formed in the nozzle body; a nozzle passage extending through the nozzle body from the nozzle body inlet to the liquid nozzle opening; wherein the nozzle body inlet is positioned over the nozzle port on the barrel when the integrated air cap/nozzle is attached to the barrel adaptor such that liquid entering the nozzle passage through the nozzle port exits from the nozzle passage through the liquid nozzle opening; a front wall comprising a center air outlet; a nozzle body attached to the integrated air cap/nozzle, the nozzle body comprising an inlet end and a nozzle outlet end; a liquid nozzle opening formed in the nozzle outlet end of the nozzle body; a nozzle body inlet formed in the nozzle body; a nozzle passage extending through the nozzle body from the nozzle body inlet to the liquid nozzle opening; wherein the nozzle body inlet is positioned over the nozzle port on the barrel when the integrated air cap/nozzle is attached to the barrel adaptor such that liquid entering the nozzle passage through the nozzle port exits from the nozzle passage through the liquid nozzle opening; wherein, when attached to the barrel adaptor, the integrated air cap/nozzle defines a center air chamber that extends from the barrel plate to the center air outlet in the integrated air cap/nozzle, wherein air enters the center air chamber through the center air aperture in the barrel plate before passing out of the center air outlet during use of the spray head assembly; wherein removal of the integrated air cap/nozzle from the barrel adaptor removes the nozzle body from the nozzle port of the barrel adaptor, and the nozzle body is configured to be remaining attached to the body of the integrated air cap/nozzle.