Quantcast OPERATION OF THE MAIN FUEL FILTER

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dome-shaped head that provides an even, unrestricted flow of fuel from the separator elements. A test connection for obtaining a sample of the fuel being discharged is located at the bottom of the outlet chamber. When it is necessary to drain the filter com- pletely, the outlet chamber is drained into containers through this line. Two pressure gages (one for each chamber) and a differential pressure gage are installed on a gage board conveniently located in the filter room. These gages are provided for determining the pressure drop across the filter elements. A shutoff valve is installed in each gage line to permit removal of the gages for maintenance. OPERATION OF THE MAIN FUEL FIL- TER.— It is imperative that the filter be properly vented so full use of all filtering elements will occur. JP-5 enters the inlet chamber of the filter. The JP-5 then passes to the inside of the coalescing elements, where solids 5 microns and larger are retained on the inner walls of the elements. As the JP-5 passes through the elements into the fallout chamber, any water is coalesced into large droplets on the outside of the elements. These water droplets fall out of the JP-5 by gravity and into the sump as the JP-5 passes across the fallout chamber to the separator elements. JP-5 enters the separator elements from the outside and, as it passes through the elements to the outlet chamber, any final traces of coalesced water that did not fall are repelled. The JP-5 then leaves the outlet chamber of the filter from the top and flows through the automatic shutoff valve into the forward and aft legs of the quadrant. Rated capacity is 2,000 gpm. CAUTION Exercise care at all times when opening and closing valves that govern flow through the filter to prevent a hydraulic hammer shock to the filter. This may overstress the housing or rupture the filter elements. Immediately after a filter with new elements is placed in operation, the pressure gages must be read and the pressures logged. A pressure differential between the inlet and fallout chambers should be noted. This pressure drop will increase in time due to the buildup of solid contaminants on the inner walls of coalescing elements. Pressure Checks.— The inlet, outlet, and differen- tial pressure gages should be read and recorded as indicated in the filter operating log. As solids build up on the elements, the pressure drop across the filter increases. The differential gage determines the actual differential pressure across the entire filter assembly. The pressure drop across the coalescer elements is the most critical. As the maximum allowable pressure drop across the coalescing elements is reached, they fail to perform their designed function and must be replaced. The maxi- mum allowable pressure drop limits for coalescer ele- ments are found on the instruction sheet in the manufacturer’s packing crate. Although pressure drop limits may vary, 15 psi is the typical pressure drop limit. Sample Checks.— Daily checks are taken from the filter sump and outlet chamber at the beginning of initial flow and every 15 minutes thereafter. The contents of each sample should be recorded in the operating log. These samples can be used to determine the condition of the coalescer and separator elements. If the sample taken from the filter sump contains solids, it is a probable indication that the coalescer elements have failed. If the sample taken from the outlet chamber is contaminated, it is a probable indication that the coalescer and/or separator elements have failed. In either case, the elements should be inspected and re- placed as necessary. Also, coalescer elements should be replaced at each overhaul and before deployment. If no overhaul or deployment occurs, they should be replaced in accord- ance with PMS. When coalescer elements are replaced, separator elements should be cleaned and inspected. Only defective separator elements need be replaced. Coalescer elements of one manufacturer may be used with the separator elements of another manufacturer. FILTER HYDRAULIC CONTROL SYS- TEM.— The filter hydraulic control system is a safety device installed on all fuel filters. It functions to drain automatically the accumulated water from the filter sump, and to shut off the filter flow if more water accumulates than can be drained off automatically. This system consists of three hydraulic control valves and afloat operated control valve. Two hydraulic control valves (the automatic shutoff valve and pilot valve) are located in the filter discharge line. The other hydraulic control valve (the automatic water drain valve) is located in the filter sump drain line. The float operated control valve (rotary valve) is located on the side or bottom of the filter sump. Automatic Shutoff Valve.— The automatic shut- off valve is of a modified globe valve design, using a well supported and reinforced diaphragm as a working means. A tension spring located in the upper valve chamber (above the diaphragm) assists in seating the valve when closing, and provides a cushioning when 4-29



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