Abstract: A gas purification system through a filter system, especially applicable to an internal combustion engine, comprising engine exhaust ducting, an exhaust pipe, an expander on the exhaust pipe between a muffler and the exhaust ducting, a duct connected to the expander for diverting escape gases from the exhaust pipe, a pressure reducer on the duct to suck the gases from the exhaust pipe, a series of filtering parts serially interconnected on the duct between the expander and the pressure reducer to filter the gases, a regulator located between the pressure reducer and the filtering parts, a relay connected to the pressure reducer to start or stop the operation of the pressure reducer, a contactor connected to the engine to detect changes in the engine speed, an electronic circuit connected to both the relay and contactor so as to signal the relay when the contactor detects that the engine is idling or beginning to accelerate, and a delay switch connected to both the relay and electronic circuit so as to momenta