an electrostatic powder spray gun comprises a powder cup and is constructed such that the powder cup comprises a removable cover which is secured to the pistol tube of the gun in an easily - detachable manner , whereby a conveying tube and an air tube extend through the cover and are held thereat . the air tube projects beyond the cover and , given the cover secured to the pistol tube , projects into a spring - loaded discharge valve of the compressed air feed line and thereby holds the same in the open position against spring pressure . given the cover secured to the pistol tube , the orifice of a powder channel extending in the pistol tube is constructed as a connection for a powder feed line leading from a remote powder preparation system .