Two-Stage Fluid Filters.

Figure 4-99. Differential Pressure Indicator (Normal Flow)

TM-1-1500-204-23-2 General Aircraft Maintenance (Pneudraulics Maintenance and Practices) Volume 2 Manual
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TM 1-1500-204-23-2 2 Depressurize reservoir (if necessary). 3 Cut lockwire. 4 Unscrew the filter case and remove it from the filter head, using a slight rocking and downward pull on the case after the case threads are free from the filter. 5 Extract the retaining ring and remove the filter element from the cases. 6 After ensuring that a replacement filter element is available, cut the filter element. 7.Before Installing the new filter, clean the filter head and the filter case and inspect them for damage; replace all damaged parts. 8 Replace all O-ring packings 9 Fill the filter bowl with new fluid before attaching it to the filter housing head. Filling the bowls helps to stop the Injection of air into the system 10 Install the filter in its case and screw the case into the filter head. The correct torque is usually handtight plus one-eighth of a turn, but always check the specific maintenance manual for the specific torque value. 11. Pressurize the hydraulic system and inspect the filter assembly for leaks. If the assembly is Satisfactory, replace the lockwire between the filter case and the head assembly. (2) Stainless steel elements. Stainless steel filter elements are used in most modern aircraft. Filter element surfaces of this type usually have a corrugated stainless steel mesh construction. Such filters are usually rated from 5to 10-micron nominal flow and at 25micron absolute flow. This means about 95 percent of 5to 10-micron particles and 100 percent of 25-micron particles will be filtered from the fluid. The curved passages of the filter element limit the length of the particles that pass through the filter. WARNING Drycleaning solvent is flammable and solvent vapors are toxic. Use P-D-680, Type II Solvent in a well- ventilated area Keep away from open flames. Avoid prolonged solvent contact with skin. CAUTION Under no condition shall a wire brush be used in cleaning filter element. Failure to comply will result in possible failure of equipment. CAUTION The use of any alcohol in cleaning components which contact hydraulic fluids is prohibited Formation of a polymeric residue can result which could impair mechanical operation of the component. (a) Wash filter element In drycleaning solvent, Federal Specification P-D-680, using a soft lint-free cloth Allow to drain, and dry with low pressure compressed air (b) Replace filter element when cracks, tears, and other signs of deterioration are noted. d. Two-Stage Fluid Filters. Two-stage line-type hydraulic system filters are being used in some recent aircraft models The typical two-stage filter has two filter elements, two bypass valves, and two differential pressure indicators The first-stage element can filter out smaller particles than the second-stage element can. Normally, the fluid passes through both elements, flowing first through the first stage element. As long as the first stage element is unclogged and functioning, there will be no foreign matter left for the second-stage element to remove. However, if the first-stage element becomes clogged, its bypass valve opens and fluid goes directly from the filter inlet port to the second-stage element, which then takes over the job of filtering out foreign particles Although the second-stage element is not capable of filtering out the very small particles, it can be safely used until the first-stage element is unclogged. 4-108

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