This set-up is used to print highly viscous fluids or pastes. From a central compressed air supplyment the air is lead through pressure regulators and 3/2-way valves to the syringes. An electrical circuit containing solid state relais controls the valves. The switch signal is a gcode command that triggeres an unused arduino port (marlin firmware). To insert these gcode commands before and after each travel move I used a postprocessing python script with slic3r.The entire set-up is based upon the possibility of unused, controllable ports on the printer's mainboard. In my case the printer is run by an Arduino Mega 2560. In Marlin/Sprinter firmware 'M42 Pxxx Syyy' (xxx=pin number, yyy=0 to 255) switches a general purpose I/O pin. With the 5V DC signal from the Arduino Board a solid state relais (Sharp S202 S02) controls the 230V AC for the solenoid valve. I also added the python script which automatically inserts the gcode commands. It can be used with slic3r (Print Settings -> Output Options -> Post-processing Scripts). The idea of the script is fairly simple. Bevor and after each travel move (indicated by the string "F12000" at the end of a line) the script inserts an open and close command.