Thrust test for the Axial Jet fans are conducted in accordance to ISO 13350, "Industrial fans – Performance testing of Jet Fans” and ANSI/AMCA 250-05, "Laboratory Methods of Testing Jet Tunnel Fans for Performance". According to ISO 13350, friction in tunnel walls, inlet and outlet losses and occasionally traffic drag together with climatic changes within the tunnels can create a pressure drop through the tunnel. This pressure drop is equivalent to the summation of the pressure increased generated by the jet fans caused by the momentum transfer between the fan discharge airflow and airflow within the tunnel. The rate of change in momentum is equal in value to the Thrust, which can be measured.