The purpose of my thesis is to study the behaviour of the small gas flows in the pipes in fuction of the supply pressure. Have been used some calibrated leaks that, in function of the supply pressure, generate a constant mass flow rate. The leaks chosen are made by the ATEQ Italia s.r.l. both for ease of use and precision that they guarantee. It was necessary to do a calibration of these leaks using an instrument called “Micro-gas” (a piston inside a cylinder) that joined with a software called “LabView” gives me the possibility to collect the various parameter of the calibration like: mass flow rate, initial and finale temperature and pressure, path of the piston, velocity of the piston.