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Page Title:
Operation over unrestrained areas |
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|  MIL-G-5514G
over which, or through which, packings confined in glands must be inserted at
installation, shall be of such size that there will be a diametrical clearance
between the packings and the thread at the most unfavorable extreme
tolerances. Chamfered edge annular undercuts shall be used at all
cross-holes; in addition, chamfers shall be used at the ends of bores with
sloped areas clear of intersecting holes. This is required because where a
packing under squeeze crosses even a round edge cross-hole, it may be
partially severed as a result of localized protrusion. Typical methods of
undercutting and chamfering, as well as illustration of pinched packings,
which are to be avoided, are shown in Figure 1.
3.1.2 Operation over unrestrained areas. Mechanisms which require that the
packing pass over holes, ports, step diameters, etc., which would leave the
ID, OD, or sides of the seal unrestrained during its normal operation, shall
be avoided. If, however, it is necessary to deviate from the above,
qualification tests satisfactory to the Services must be performed to
substantiate the design. In such tests, consideration shall be given to: (a)
Use of the appropriate highest swell-approved packings, (b) aging in the
appropriate highest swell-approved fluid, (c) adverse maximum packing squeeze
if such test conditions are warranted by analysis of the particular design.
The Services will designate the applicable high-swell packing and fluid upon
request.
3.1.2.1 Dynamic seal travel. A running seal gland shall be so located in a
component that the leading edge of the groove or gland, at its position of
extreme travel or adjustment including adverse tolerances, shall remain
sufficiently distant from the nearest edge of any chamfer, undercut, or other
departure from the bore, or equivalent diameter, that there can be no
extrusion, cutting, or other damage to the seal throughout the operating
pressure and temperature ranges. In general, the same practice applies to
static seals.
3.1.3 Gland materials. Materials used in the manufacture of packing glands
shall be in accordance with the requirements of the detail specification.
All material used in packing glands shall satisfactorily resist corrosion
during its normal service life.
3.2.4 O-rinq packing gland dimensions. O-ring packing glands, both nominal
and otherwise, should be made to the recommended requirements indicated
herein. A nominal o-ring installation shall be considered one that uses a
cylinder bore or piston rod having the equivalent dimensions (see Figure 2}
and corresponding to the O-rings as listed in Table I herein. Nominal glands
shall be used wherever possible.
3.1.4.1 Nominal sized installations. Dimensions, tolerances, and allowable
eccentricities for piston rods, cylinder bores, and rod and head gland groove
diameters, lengths and shapes, and allowable diametrical clearances for
nominal O-ring installations shall be carefully selected and closely
controlled in order to provide for required service life, prevention of
extrusion minimum leakage, and freedom from binding throughout the required
range of operating temperatures and pressures. For glands to seal up to and
including 1,500 psi pressure, the data given in Table I of this specification,
under the column titled "No backup rings," are suitable for Type I systems.
For glands to seal up to and including 3,000 psi pressure, the data given in
Table I of this specification under the columns titled "One backup ring" and
"Two backup rings" are suitable for Type I and Type II systems.
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