Filtering device configured to be immersed at least partially in a fluid to be filtered and comprising at least one main filter and a filter holder supporting the main filter, the filtering device being configured to be moved inside the fluid and; wherein - the filter holder comprises a body and at least one first and a second valve units (103, 107, 103', 107', 800, 800'), characterized in that - the body and the two valve units (103, 107, 103', 107', 800, 800') defining a filtering chamber inside of which the main filter is arranged; - the main filter has an outer wall (16, 16') turned next to the body and an inner wall (15, 15') opposite to the outer wall (16, 16'); the main filter delimiting in the filtering chamber, an inner portion and an outer portion of the filtering chamber located on either side of the inner and outer walls of the main filter; - the filter holder comprises at least one inlet opening (108, 708') defined by the first valve unit (107, 800') and at least one first intake valve (106, 706') cooperating with the inlet opening (108, 708') and configured to allow the fluid to pass through the inlet opening (108, 708') only when the filtering device is moved in a first movement direction; - the filter holder comprises at least one outlet opening defined by the second valve unit (103, 800') and at least one first release valve (102, 702) cooperating with the outlet opening and configured to allow the fluid to pass through the outlet opening only when the filtering device is moved in said first movement direction; - the first intake valve (106, 706') being arranged upstream of the first release valve (102, 702) with respect to the direction of flow of the fluid in the filtering device when the latter is moved in the first movement direction; - the passage of the fluid through the inlet opening (108, 708') allowing the fluid located upstream from the filtering device when the latter is moved in the first movement direction to penetrate into the filtering chamber; - the passage of the fluid through the outlet opening allowing the fluid located in the filtering chamber to flow outside of the filtering chamber when the filtering device is moved in the first movement direction; - the inlet opening (108, 708') and the outlet opening being arranged in such a way that when the filtering device is moved in said first movement direction, the fluid passes through the main filter in a first filtering direction to pass from the inlet opening (108, 708') to the outlet opening; - the filtering device being configured in such a way as to prevent the fluid from passing through the main filter in a second filtering direction opposite to the first filtering direction when the filtering device is moved in a second movement direction opposite to the first movement direction. - the filter holder comprises a body and at least one first and a second valve units (103, 107, 103', 107', 800, 800'), - the body and the two valve units (103, 107, 103', 107', 800, 800') defining a filtering chamber inside of which the main filter is arranged; - the main filter has an outer wall (16, 16') turned next to the body and an inner wall (15, 15') opposite to the outer wall (16, 16'); the main filter delimiting in the filtering chamber, an inner portion and an outer portion of the filtering chamber located on either side of the inner and outer walls of the main filter; - the filter holder comprises at least one inlet opening (108, 708') defined by the first valve unit (107, 800') and at least one first intake valve (106, 706') cooperating with the inlet opening (108, 708') and configured to allow the fluid to pass through the inlet opening (108, 708') only when the filtering device is moved in a first movement direction; - the filter holder comprises at least one outlet opening defined by the second valve unit (103, 800') and at least one first release valve (102, 702) cooperating with the outlet opening and configured to allow the fluid to pass through the outlet opening only when the filtering device is moved in said first movement direction; - the first intake valve (106, 706') being arranged upstream of the first release valve (102, 702) with respect to the direction of flow of the fluid in the filtering device when the latter is moved in the first movement direction; - the passage of the fluid through the inlet opening (108, 708') allowing the fluid located upstream from the filtering device when the latter is moved in the first movement direction to penetrate into the filtering chamber; - the passage of the fluid through the outlet opening allowing the fluid located in the filtering chamber to flow outside of the filtering chamber when the filtering device is moved in the first movement direction; - the inlet opening (108, 708') and the outlet opening being arranged in such a way that when the filtering device is moved in said first movement direction, the fluid passes through the main filter in a first filtering direction to pass from the inlet opening (108, 708') to the outlet opening; - the filtering device being configured in such a way as to prevent the fluid from passing through the main filter in a second filtering direction opposite to the first filtering direction when the filtering device is moved in a second movement direction opposite to the first movement direction.