MIL-DTL-16356E
3.12.7.1 Spring cone washers. Spring cone washers shall be used as part of all body and cover clamping
designs. Spring cone washers shall be at least equal to 17-7 PH corrosion-resisting steel. Spring cone washers shall
be scale free and show no discoloration or lack of uniformity from heat treatment. The final finish shall have no
scale, sharp edges, or imperfections. Spring cones as part of shouldered cap screw assemblies for Class IV gauges
shall be PH 15-7 Mo alloy in accordance with SAE-AMS-5520. The cap screw assembly with PH15-7 Mo spring
cones shall be compression tested in accordance with 4.4.1.8.2. Three randomly selected samples shall be tested for
lots up to 150 units. Sample size for lots above 150 units shall be in accordance with ASQ H1331 at Inspection
Level S-2. Spring cones used to assemble cap screw assemblies shall be randomly selected. Three sample bolts,
assembled with required six washers, shall have stiffness (slope of curve) in the linear region between 0.010 and
0.020 inches of deflection between 110,000 and 225,000 pounds per inch. Variation between the three samples shall
not exceed 25,000 pounds per inch. After one deflection to ⅔ of its formed height per 4.4.1.8.2.b, a sample spring
cone washer shall return to its original height within ±0.002 inch of its original height. The washers shall withstand
the repeated load test specified in 4.4.1.8.2.c without indication of permanent set in excess of 10 percent of the
original free height and without cracking or breaking. The heat treatment procedure, to the requirements of
SAE-AMS-5520 for austenite conditioning and precipitation heat treatment, shall be tested and approved in
accordance with 4.4.1.8.2.a. This testing and approval requires that heat processing equipment meets the pyrometric
requirements of a Class 2 parts furnace in accordance with SAE-AMS-2750. The heat treatment facility shall have
Nadcap industry certification provided by the Performance Review Institute (www.pri-network.org/nadcap/) in
association with SAE International. A furnace Temperature Uniformity Survey (TUS) shall be conducted in
accordance with Class 2 requirements described in 4.4.1.8.2.a. Spring cones shall be hardness tested in accordance
with 4.7.6.2.
3.12.7.2 Thread protrusion. Gauges fully assembled and tightened for service, with manufacturer s
recommended insert materials, shall have all stud or bolt threads protruding beyond the nut by at least two full
threads. Stud and bolt lengths shall be established to make thread protrusion equal on all fasteners. Refer to 4.6.1
visual examination requirements.
3.12.8 Chain guides. Shut-off valves on Class I, II, and IV gauges shall be equipped with sprocket wheels and
guides. The sprocket wheel shall have a chain guide pivoting from the sprocket center. The guide shall hang below
the sprocket in such a way that it will direct the chain on and off the sprocket. Provision shall be made to protect the
chain guides and to preclude slippage of the chain from the wheel. In addition for Class IV service, chain stops shall
be provided for 3.12.9.2 chain pull requirements.
3.12.9 Gauge fittings.
3.12.9.1 Nipples and connector. The connecting tubes shall be welded into the frame (see 3.9.1). The frame
shall be removed from the connectors or valves without removal of the fittings from the boiler to which the gauge is
attached. Connectors shall have a minimum of two-hole flanges. The end stem or end connectors shall be slotted so
that the frame may be disengaged from the valves or end connectors without springing the expansion loop. The
length of the tubular connecting pieces shall suit the distance between centers of the top and bottom fittings as
installed on the boiler. Union fittings shall not be permitted. Dimensions shall be in accordance with
5000-S5100-841604.
3.12.9.2 Shut-off valves. One chain pull of 3 feet shall allow sufficient valve opening for spontaneous gauge
action. Top valve shall also include expansion loop to allow movement, which is not to exceed ±⅛ inch in the valve
frame relationship. Shut-off valves shall use single threads. Nominal size shall be ½ inch. Failure or leakage of the
gauge of 200 pounds per hour or less of saturated steam shall cause the bottom automatic check valve to close.
Arrangement of the ball-check valves in the gauge assembly shall preclude seating of the balls under pitch and roll
conditions up to 60 degrees. The closed bottom check valve shall seal without ball extrusion, seat deformation, or
leakage of more than 100 centimeters cubed per hour.
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