Filters cannot be applied to filtering out foreign matters included in a fluid, such as a fruit juice containing fibrous materials because filters are clogged up with the fibrous materials. 
A previously proposed apparatus for eliminating foreign matters included in such a fluid guides the fluid into a plurality of narrow passages by gravity, monitors the fluid flowing through the narrow passages by detectors, and opens a valve placed in the narrow passage upon the detection of a foreign matter included in the fluid flowing through the same narrow passage by the detector to discharge the foreign matter from the narrow passage (Patent document 1). 
A previously proposed fibrous matter detecting and eliminating apparatus for detecting and eliminating foreign matters included in a fluid uses a fluid carrying pipe provided with an inspection window, illuminates the fluid through the inspection window by an illuminating means, measures transmitted light transmitted by the fluid or reflected light reflected by the fluid, converts the transmitted or reflected light into an image signal, compares a signal level based on the image signal with a reference signal level to decide where or not the fluid includes foreign matters, and eliminates the foreign matters when it is decided that the fluid includes foreign matters (Patent document 2)
Patent document 1: JP 10-43695 A
Patent document 2: JP 2000-235004 A
The apparatus mentioned in Patent document 1 uses the pressure head of the fluid to guide the fluid into the narrow passages by gravity.  Therefore, the fluid is not distributed uniformly to the narrow passages in the middle part and those in the end parts of the apparatus, different pressures act on the narrow passages, and the velocity of the fluid in the narrow passage nearest to a supply line and that of the fluid in the narrow passage farthest from the supply line are liable to differ from each other.  Consequently, foreign matters cannot be eliminated with reliability and the fluid cannot be processed at a high processing speed. 
Since reflected light is used for detecting foreign matters, the detector has difficulty in detecting foreign matters in the middle layer of the flow of the fluid when the tint of foreign matters is similar to that of the fluid or when foreign matters are small as compared with the length of a detecting optical path.  Thus the apparatus is unable to detect foreign matters in high detecting accuracy at a high processing speed. 
The fibrous matter detecting and eliminating apparatus mentioned in Patent document 2 uses a pipe having a circular cross section and provided with an inspection window.  Although this apparatus is applicable to detecting and eliminating foreign matters included in a fluid having a high transparency, the same is not applicable to detecting and eliminating foreign matters included in a fluid having a low transparency, such as a fruit juice containing fibrous materials, because the inspecting light is unable to penetrate the fluid diametrically. 
As mentioned above, fluids, such as beverages including fibrous components and liquid medicines, clog up filters and the fibrous components included therein make the detection of foreign matters difficult. 
Since the transparency of fruit juices is particularly low, optical detection of foreign matters included in fruit juices is difficult.  Therefore, the optical detection of foreign matters needs to use an optical path of the shortest possible length and to use an algorithm that will not mistake fibrous components or bubbles often adhering to fibrous components for foreign matters. 
The passage must be divided into narrow passages and make the fluid flow at the same velocity through all the narrow passages to eliminate foreign matters completely and to reduce the quantity of the fluid that is removed together with foreign matters. 
It is important in detecting and eliminating foreign matters included in a fluid including such kind of fibrous components to distribute the fluid uniformly into narrow passages by pressure and to avoid clogging the narrow passage even if the fluid includes fibrous components.