TM 1-1500-204-23-2a.FlarelessFittings. The main feature of MSfittings is that they can be used to connect unflaredtubing. An MS fitting has a counterbore in which thetube end is Installed. In the half-sectional view of anMS fitting in figure 4-17, notice the 24-degree beveledportion of the counterbore and its seat. The seat formsa slope for the tube during the connection of one tubeto another tube or for a tube to a component and thebeveled area causes the tube connector sleeve to sealthe connection as the tube B-nut is tightened.(1) Identification of flareless fittings. MS fit-tings are made of aluminum alloy or steel Aluminumalloy fittings can be identified visually by their yellowcolor, which is caused from the anodizing treatment.The cadmium plating on steel fittings are identified byletter-number codes; for example, MS21900-4, whichis interpreted as follows:MS........prefix (military specification)21900...design part number (adapter, flare-less tube to AN flared tube)4..........size of fitting in sixteenths of an inch (4/16 (inch)The material from which the fittings are made is indi-cated by the absence of a letter at the end of the MSnumber or by the addition of a letter at the end of thenumber, for example:MS21900-4 is made from carbon steelMS21900-8-D is made from aluminumalloyMS21900-8-S is made from corrosion-resistant steel, class 347(2)Types of flareless fittings.See figure 4-18for examples of MS flareless fittings.WARNINGCompressed air shall not be used for cleaning pur-poses unless reduced to less than 30 psi and thenonly with effective chip-guarding and personalprotective equipment.(3) Installation of flareless fittings. MS fittingsmust be inspected before Installation. If It Is Impossibleto see through a fitting or tube, blow clean, dry com-pressed air through it to be certain that no obstructionsexist. Any lines that have caps removed in storage orbefore installation should be flushed with cleanhydraulic fluid. Male threads and sleeves of the fittingsbeing assembled should be lubricated with the type ofhydraulic fluid used in the system On fittings withtapered threads, use antiseize compound on thethreads, except for the first three, which are left dry.(a) Gasket. To make a connection be-tween tubing and a component, the proper gasket isselected, lubricated, and Installed In position as shownin figure 4-19. The fitting is screwed into the boss of thecomponent until it bottoms on the boss.(b) Installing tubing. When connectingtubing to an MS fitting, the tube should be aligned withthe fitting and the nut should be started by hand withoutexcessive strain on the line (see figure 4-20). Do notuse force to align tubing Tube alignment can often beobtained by loosening clamps on connecting lines orby rotating fittings. Both ends of the tubing should beconnected and tightened until a decided increase Inresistance to turning of the B-nut is encountered. Atthis point, tighten the clamps, ensuring that they do notpull the tubing out of alignment and place it in a bindingposition. Complete the installation by turning the B-nutone-sixth of a turn. See figure 4-21 for turns and torquevalues. Pressurize the hydraulic system and Inspect forleaks. If leakage is noted, release system pressure andcompletely loosen the B-nut. If possible, rotate thesleeve to a new position and then retorque the B-nutto its previous position plus one-sixth of a turn. Normal-ly this will stop the leak, but If it does not, replace theassembly.4-15
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