Vacuum pump for lowering pressure in a device, the vacuum pump comprising a vacuum chamber with a chamber wall; wherein the chamber wall comprises a minor point, which is the point of the chamber wall where the distance between the chamber wall and the rotor is minimum, and a maximum point, which is a point where a first virtual size vane is placed so that the volume enclosed by the first virtual size vane, a second virtual size vane preceding to the first virtual size vane is maximum; a rotor housed in the vacuum chamber, this rotor comprising at least one slot; at least one vane (4, 41, 42), each vane (4, 41, 42) being at least partially introduced in one slot of the rotor; at least one fluid inlet being located between a first inlet point of the chamber wall and a second inlet point of the chamber wall, the first fluid inlet being suitable for being in fluid communication with the device where pressure is aimed to be lowered; and a primary fluid outlet being located between a first primary outlet point of the chamber wall and a second primary outlet point of the chamber wall, the primary fluid outlet being in fluid communication with a first outside fluid zone of the vacuum pump; a secondary fluid outlet being located between a first secondary outlet point of the chamber wall and a second secondary outlet point of the chamber wall, the secondary fluid outlet being in fluid communication with a second outside fluid zone of the vacuum pump, the distance between the first secondary outlet point and the minor point being lower than the distance between the first primary outlet point and the minor point; wherein a volume of the chamber wall defined by a first virtual outlet vane in contact with the first secondary outlet point and a second virtual outlet vane which is subsequent to the first virtual outlet vane is greater than a volume of the chamber wall defined by a third virtual outlet vane in contact with the second primary outlet point and a fourth virtual outlet vane which is preceding to the third virtual outlet vane; wherein the primary fluid outlet comprises primary blocking means adapted for sealing the fluid communication between the primary fluid outlet and the first outside fluid zone if the pressure in the primary fluid outlet is lower than a first predetermined value; and wherein a compression zone is defined in the vacuum chamber, the compression zone being limited by a first virtual compression vane located in contact with a major point; the major point being either the second inlet point or the maximum point; a second virtual compression vane located in contact with the minor point; a portion of the rotor comprised between these two first and second virtual compression vanes, considered in the direction from the first virtual compression vane to the second virtual compression vane; and a portion of the chamber wall between the major point and the minor point, considered in the direction from the first virtual compression vane to the second virtual compression vane and wherein the fourth virtual outlet vane is comprised within the compression zone. a vacuum chamber with a chamber wall; wherein the chamber wall comprises a minor point, which is the point of the chamber wall where the distance between the chamber wall and the rotor is minimum, and a maximum point, which is a point where a first virtual size vane is placed so that the volume enclosed by the first virtual size vane, a second virtual size vane preceding to the first virtual size vane is maximum; a rotor housed in the vacuum chamber, this rotor comprising at least one slot; at least one vane (4, 41, 42), each vane (4, 41, 42) being at least partially introduced in one slot of the rotor; at least one fluid inlet being located between a first inlet point of the chamber wall and a second inlet point of the chamber wall, the first fluid inlet being suitable for being in fluid communication with the device where pressure is aimed to be lowered; and a primary fluid outlet being located between a first primary outlet point of the chamber wall and a second primary outlet point of the chamber wall, the primary fluid outlet being in fluid communication with a first outside fluid zone of the vacuum pump; a secondary fluid outlet being located between a first secondary outlet point of the chamber wall and a second secondary outlet point of the chamber wall, the secondary fluid outlet being in fluid communication with a second outside fluid zone of the vacuum pump, the distance between the first secondary outlet point and the minor point being lower than the distance between the first primary outlet point and the minor point; a first virtual compression vane located in contact with a major point; the major point being either the second inlet point or the maximum point; a second virtual compression vane located in contact with the minor point; a portion of the rotor comprised between these two first and second virtual compression vanes, considered in the direction from the first virtual compression vane to the second virtual compression vane; and