Abstract: The invention provides an electrostatic spray gun including a replaceable fluid container a nozzle outlet, apparatus for applying high voltage to the liquid and a spring loaded trigger piston for pressurizing the liquid through the outlet. The piston has axially inner and outer parts for forming a lubricant chamber therebetween. The lubricant seals the paint forward of the piston during pressurization and prevents the piston from being locked up during reciprocation.