be adjusted without having to turn for the purpose the pressure measuring device relative to the gun body the pressure display 39 of the pressure measuring device can be read off well for this reason with each setting of regulation of the supply of compressed air the pressure measuring device can be easily affixed in a removable manner on the device for regulation of the supply of compressed air by means of affixing elements 41 49 this makes possible a simple and rapid manual removal of the pressure measuring device without the aid of a tool if it for example is a disturbance during varnishing operations in sites which are difficult to access due to the simple removal of the pressure measuring device 35 it is also possible to use the pressure measuring device for several different spray guns without a complicated dismantling or installing being required in the gun bodies from other spray guns moreover due to the simple removal possibility of the pressure measuring device from the device for regulation of the supply of compressed air a simple battery replacement is also made possible with digital pressure measuring devices for cleaning operations on the spray gun also the pressure measuring device can be removed simply so that it is not soiled or damaged this is particularly advantageous when using automatic pistol cleaning devices the pressure measuring device 35 with the advantages described.