A spray gun with a removable paint cartridge, whereby the paint cartridge is comprising - a tubular body with a nozzle at its front end, - a needle valve assembly with a needle valve member extending through the tubular body of the cartridge and connecting to a trigger on the spray gun, the needle valve member having an apex for engaging an aperture in the nozzle on the paint cartridge for allowing paint to flow out when the needle valve member is withdrawn from the aperture, - a tubular connection from the paint cartridge to a paint supply, and whereby the spray gun is composed of a front portion and a rear portion and is comprising - a means for holding the paint cartridge securely in place in the spray gun, - a spray head assembly arranged on the front portion of the spray gun adjacent the aperture on the nozzle of the cartridge to deliver an air stream when the trigger moves the needle valve member in the paint cartridge to open the aperture for entraining paint from the nozzle, - and a paint cartridge chamber for inserting the paint cartridge, characterized in that - the front portion being connected with the rear portion by connection means, allowing the paint cartridge to have access to the paint cartridge chamber when the connection means is in an open position and locks the paint cartridge in the paint cartridge chamber when the connection means is in a closed position, - the cartridge has a rear end with an aperture for allowing the needle valve member to slidably pass therethrough, - and that a spring is arranged in the tubular body of the cartridge and is biasing the needle valve member forward into the aperture of the nozzle to prevent fluid from escaping the tubular body. - a tubular body with a nozzle at its front end, - a needle valve assembly with a needle valve member extending through the tubular body of the cartridge and connecting to a trigger on the spray gun, the needle valve member having an apex for engaging an aperture in the nozzle on the paint cartridge for allowing paint to flow out when the needle valve member is withdrawn from the aperture, - a tubular connection from the paint cartridge to a paint supply, and whereby the spray gun is composed of a front portion and a rear portion and is comprising - a means for holding the paint cartridge securely in place in the spray gun, - a spray head assembly arranged on the front portion of the spray gun adjacent the aperture on the nozzle of the cartridge to deliver an air stream when the trigger moves the needle valve member in the paint cartridge to open the aperture for entraining paint from the nozzle, - and a paint cartridge chamber for inserting the paint cartridge, - the front portion being connected with the rear portion by connection means, allowing the paint cartridge to have access to the paint cartridge chamber when the connection means is in an open position and locks the paint cartridge in the paint cartridge chamber when the connection means is in a closed position, - the cartridge has a rear end with an aperture for allowing the needle valve member to slidably pass therethrough, - and that a spring is arranged in the tubular body of the cartridge and is biasing the needle valve member forward into the aperture of the nozzle to prevent fluid from escaping the tubular body.