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Use of straight thread tube fitting boss packing |
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|  MIL-G-5514G
3.5.4.1 Type I systems. Static seals conforming to MS28775, MIL-P-83461/1,
and MIL-P-87175/l at pressures up to and including 1,500 psi, provided the
clearances, eccentricities, and other requirements of Table I are not
exceeded. Above 1,500 psi pressure, the o-ring static seals shall be used
with the applicable backup rings in accordance with Table I. If the
diametrical clearance can be held to a maximum of 0.0025 inch under the worst
condition of tolerances, eccentricities, breathing, etc., the backup rings
need not be used.
3.5.4.2 Type II systems. Static seals conforming to MS28775, MIL-P-83461/1,
and MIL-P-87175/l should be used at pressures up to 3,000 psi with backup
rings in accordance with Table I and requirements herein on nonextrusion
devices, unless it can be proven by qualification tests that glands will
perform satisfactorily without nonextrusion backup rings.
3.5.5 Use of straight thread tube fitting boss packing.
3.5.5.1 Type I and Type II systems. The packing for type I and Type II
systems is defined by MS28778, MIL-P-5510, and MIL-P-83461/2 packing shall be
used only in connection with straight thread tube fitting glands, such as in
the boss conforming to MS33649, with end fittings in accordance with MS33656
and MS33657 assembled in accordance with MS21344, MS33514, and MS33515
assembled in accordance with MS33566. This usage includes such.
other parts as end caps on check valves wherein the dimensions of the gland
duplicate the tube fitting and boss drawings enumerated above. In certain
fitting installations, as shown on MS23344 the MS28773 nonextrusion rings must
be used with the MS28778 gasket.
3.5.5.2 Type III systems. Packing suitable for the temperature ranges of
this system which satisfactorily pass the qualification test requirements of
the fitting installation shall be used.
3.5.6 Static face seals.
3.5.6.1 Type I systems. The use of static face seals should be avoided
wherever a breathing problem exists and a submerged radial squeeze seal design
is feasible. Where static face seals are desired, packing conforming to
MS28775, MIL-P-83461, or MIL-P-87175/l may be used. In such installations the
depth of the groove shall be in accordance with Table I.
3.5.6.1.1 Desiqn details. Metallic surfaces contacting the o-ring face seals
shall have a surface finish no rougher than 32 microinches, in accordance with
ANSI/ASME B46.1-85. The cap or coverplate must be as rigid as necessary to
prevent excessive breathing which would introduce an extrusion gap at the
joint. The important feature in face seal design is to provide squeeze on the
groove section and prevent any possible radial movement of the O-ring under
pressure application. Provisions shall be made to ensure that the o-ring
cannot be displaced from its groove under any flow or pressure condition.
3.5.6.2 Type II and Type III system. Static face seals, suitable for the
temperature ranges of these systems, shall satisfactorily pass the
qualification test requirements of the installation to be used. Usage of
MS28775 seals is recommended for Type II systems.
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