MIL-DTL-2036E
APPENDIX A
A.2.3 Order of precedence. Unless otherwise noted herein or in the contract, in the event of a conflict
between the text of this document and the references cited herein (except for related specification
sheets), the text of this document take precedence. Nothing in this document, however, supersedes
applicable laws and regulations unless a specific exemption has been obtained.
A.3 REQUIREMENTS
A.3.1 Explosionproof design approval. Explosionproof equipment enclosures furnished under this
specification shall be of a design that has been approved in accordance with A.4.1. No changes or
deviations from the approved design shall be acceptable on production units without specific approval of
the contracting activity.
A.3.2 Construction. Enclosures shall be of the totally enclosed type in which no provision is made for
ventilation of the interior or relief of pressure from internal explosions.
A.3.2.1 Design strength of enclosure. The enclosure shall be of substantial construction. The
recommended minimum thickness of metal for enclosure walls is .25 inch (6.35mm) for enclosures with
an internal free volume of 125 cubic inches (2048 cubic cm) or larger, and .1875 inch (4.76mm) for
smaller enclosures. Wall thicknesses less than the recommended minimum may be used provided the
enclosure is capable of withstanding without rupture or permanent distortion an internal hydrostatic test
pressure of four times the maximum internal explosion pressure based upon calculations. For equipment
having a wall thickness less than the recommended minimum, information concerning enclosure design
strength shall be furnished (see A.4.1.1).
A.3.2.2 Joints in enclosure. Joints shall be of the metal-to-metal plane, cylindrical, stepped, labyrinth, or
threaded type (see figures A-1 through A-7). Metal joint surfaces shall be finished to 250 microinches
(maximum) (.006mm). Gaskets, O-rings, or other sealing devices may be used if they are of
incombustible material, do not interfere with the metal-to-metal fit, and are not included as part of the
required joint dimension. Paint, dope, and fillers shall not be used on joints.
A.3.2.2.1 Plane and cylindrical joints. Requirements for dimensions of plane and cylindrical joints are
shown on figure A-1, which also illustrates typical joint construction.
A.3.2.2.2 Stepped joints (rabbet joints). Requirements for dimensions of stepped joints are shown on
figure A-2, which also illustrates typical joint construction.
A.3.2.2.3 Threaded joints. Threaded joints shall have a minimum of five full threads of engagement or a
minimum axial joint width (length of thread engagement measured straight across threads) of .5 inch
(12.7mm), whichever is greater. All screw threads shall be class 2 fit in accordance with FED-STD-
H28/2. Threaded parts shall be secured against loosening with a supplementary screw or by safety
wiring that does not penetrate the joint. A typical threaded joint is illustrated on figure A-3.
A.3.2.2.4 Drive shaft joints. Requirements for dimensions of drive shaft joints are shown on figure A-4
which also illustrates typical joint construction.
A.3.2.2.5 Operating shaft (rod) joints. Operating shafts or push rods passing through the walls of
explosionproof enclosures shall be circular in cross-section over that portion which traverses the wall; the
hole in the wall shall also be circular. The operating shaft or rod shall have a substantial shoulder, head,
or equivalent at the inside to prevent its accidental loss or removal from the outside, or expulsion during
explosion. Snap rings, cotter pins, or similar type fasteners are not acceptable as a means of preventing
such loss, removal, or expulsion. Requirements for dimensions of operating shaft (rod) joints are shown
on figure A-5, which also illustrates typical joint construction. The minimum length specified for the sliding
fit shall be maintained in all positions of the shaft (rod).
A.3.2.3 Holes for bolts, screws and rivets. Through holes in explosionproof enclosures shall be kept to a
minimum. Holes for bolts, screws, and so forth, shall be "blind" or bottomed if the omission of a bolt or
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