API Spec 1581:2002 pdf download.SPECIFICATIONS AND QUALIFICATION PROCEDURES FOR AVIATION JET FUEL FILTER/SEPARATORS
2.1.1 Filter/separator
A filter/separator is a vessel containing filter/coalescer and separator elements that continuously removes dirt and water from aviation jet fuel to levels acceptable for servicing modern aircraft. A filter/separator can have either a vertical or a horizontal configuration. A filter/separator can consist of multiple stages. 2.1.1.1 A two-stage system consists of filter/coalescer and separator elements contained within a vessel. The fuel flows through the filter/coalescer element(s) into the vessel and then flows through the separator element(s) to exit the vessel. 2.1.1.2 A multi-stage system consists of a two-stage system that contains one or more additional stages. Additional stages may include currently qualified devices 6 located within each separator element capable of shutting off fuel flow if the filter/coalescer and separator elements fail to remove water to an acceptable level. Additional stages may also include currently qualified devices 6 located within each coalescer element designed to remove dirt (prefilter) or contaminants (adsorption stage). 2.1.2 Filter/coalescer A filter/coalescer is an element that is capable of removing dirt and of coalescing fine droplets of water in the fuel to sizes that can be removed in the filter/separator vessel. Filter/coalescers are classified as Type S and Type S-LD (low dirt) according to the amount of dirt the elements are capable of removing as defined in Section 2.3.
2.3.3 Type S-LD filter/separators
Type S-LD filter/separators (also known as coalescer/ separators) can be used at all filtration points in an aviation fuelling system where significant levels of water but minimal amounts of dirt can be expected in the jet fuel. Examples of suitable locations could be immediately after a microfilter (used to remove dirt to acceptable levels) or at locations where acceptable dirt levels can be achieved without filtration. The qualification requirements for coalescer/separators are: (a) The Type S-LD filter/separator shall be able to maintain rated flow when it is contaminated with particulate to the level specified in Section 4 without the contamination in the effluent fuel exceeding the level specified in Section 3.1.1. (b) The Type S-LD filter/separator shall be able to effectively remove water from fuel without exceeding the effluent free-water levels specified in Section 3.1.1 when water is added according to the procedures specified in Section 4.