MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)require periodic adjustment. Any alignment or adjustmentdevices that are susceptible to vibration or shockshould have a positive locking device to assure retentionof settings. The locking device should be easy to apply andrelease, and the application and release of the lock shouldnot affect the setting of the adjustment. Traveling clampsand locking devices should be designed to avoid inadvertentrelease.Spindles for adjustments may be slotted, but the headshould be strong enough to withstand many manipulationswith a screwdriver. A method of locating and holdingthe adjusting screwdriver while in use is desirable. Ifadjustments must be made blindly, design the head toaccommodate a wrench to facilitate adjustment.Consider the use of locked-nut-and-thread adjustmentsinstead of shims. Avoid shim-type adjustments that performthe dual function of adjusting bearings and positioningunits. Where corrosion of nuts and threads may be afactor in the adjustment of large components, use corrosion-resistantmaterials.Where applicable, use variable pitch, V-belt drivers forhigh-speed applications. Use spring-loaded idler sprocketson chain drives to avoid frequent adjustments. Eliminateadjustment of hose fasteners used in low-pressure applications(air ducts) by using spring-type fasteners thatmaintain a constant peripheral pressure. When enclosedchain drives require periodic adjustment, automatic adjustersshould be provided.8-5 PREVENTIVE MAINTENANCE ANDSERVICING DESIGN CHECKLISTTable 8-4 is a checklist summarizing the design recommendationspresented in this chapter. The checklist containsseveral items that were not discussed separately inthe text. These items are included here because theirnecessity in the design is so obvious that they might beinadvertently overlooked. If the answer to any question inthe checklist is “no”, the design should be restudied toascertain the need for correction.1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.TABLE 8-4. PREVENTIVE MAINTENANCE AND SERVICING DESIGN CHECKLISTAre standard lubrication fittings used so that no special extensions or fittings are required?Are standard lubricants that are already in the federal supply system specified?Are adequate lubrication instructions (lubrication orders) provided that identify the frequency and type of lubricantsrequired?Are filler areas for combustible materials located away from sources of heat or sparking, and are spark-resistant fillercaps and nozzles used on such equipment?Are fluid-replenishing points located so there is little chance of spillage during servicing, especially on easily damagedequipment?Are filler openings located where they are readily accessible and do not require special filling adapters or workstands?Are air reservoir safety valves easily accessible and located where pop-off action will not injure personnel?Are fuel tank filler necks, brake air cocks, flexible lines or cables, pipe runs, fragile components, and like itemspositioned so they are not likely to be used as convenient footholds or handholds, thereby sustaining damage?If bleeds are required to remove entrapped air or gases from a fluid system, are they located in an easily operable andaccessible position? Are bleed valves labeled with the proper operating instructions?Are drains provided on all fluid tanks and systems, fluid-filled cases or pans, filter systems, float chambers, and otheritems designed to or likely to contain fluid that would otherwise be difficult to remove?Are drain fittings of few types and sizes used, and are they standardized according to application throughout thesystem?Are valves or petcocks used in preference to drain plugs? Where drain plugs are used, do they require only commonhand tools for operation, and does the design insure adequate tool and work clearance for operation?Are drain cocks or valves clearly labeled to indicate open and closed positions and the direction of movementrequired to open them?Do drain cocks always close with clockwise motion and open with counterclockwise motion?When drain cocks are closed, is the handle designed to be in the down position?Are drain points placed so that fluid will not drain on the technician or on sensitive equipment?Are drain points located at the lowest point when complete drainage is required or when separation of fluids is desired(as when water is drained out of fuel tanks)?Are drain points located to permit fluid drainage directly into a waste container without use of adapters or piping?Are drain points placed where they are readily operable by the technician?Are instruction plates provided as necessary to insure that the system is properly prepared prior to draining?(cont’d on next page)8-17