A venturi is a relatively low cost means of producing the vacuum to operate gyroscopic instruments (turn/bank, directional gyro and artificial horizon). It is mounted on the fuselage, parallel with the longitudinal axis of the aircraft. As the aircraft moves through the air, suction is created in the venturi throat. Since the venturi throat is connected by a tube to the gyro instrument case, air is sucked out of the instrument, causing air to enter an inlet port and strike the gyro rotor, which then spins rapidly and activates the instrument. A vacuum regulator and/or restrictor valve may be needed to limit the vacuum to that required for proper instrument operation.