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|  MIL-D-18641F(SH)
3.14.12 Dump valve. A three-way solenoid operated distillate dump valve, the solenoid being
actuated by the salinity cell located in the line provided for final delivery of distillate (after all heat
exchangers), shall be provided with the distillation unit. The valve shall be in accordance with
MIL-V-16556.
3.14.12.1 Type III. An additional solenoid operated dump valve, in accordance with
MIL-V-16556, actuated by the salinity cell located in the air ejector after condenser drain line shall
be provided with type 111 distillation units using vertical distiller condensers unless the air offtake
thereof and the air ejector are so located that there is no possibility of carry-over of salt
contaminated distillate into the after condenser.
3.14.12.2 Type II. On type II distillation units, a three-way solenoid-operated dump valve in
accordance with MIL-V-16556, actuated by a salinity cell located in the drain line from the salt
water feed heater, shall be installed in the salt water feed heater drain line. The drain line from
the air ejector after condenser shall connect to the salt water feed heater hotwell through a loop
seal.
3.14.13 Tubes. Tubes in the evaporators, vapor feed heaters, distiller condenser, stage
condensers, salt water feed heaters, and distillate coder shall be composition 90-10 in class 2
distillation units, or composition 70-30 in class 1 distillation units, in accordance with MIL-T-15005.
Tubes shall normally be 5/8 inch outside diameter (od), number 18 Birmingham wire gauge (BWG)
(0.049 inch wall thickness). In small capacity units of up to 5,000 gallons per day of distillate, when
the use of smaller diameter tubes will result in fewer passes in the above heat exhangers, the tubes
may be 3/8 inch od, number 18 BWG. In some submarine usage, the tubes may be required
thicker than number 18 BWG (see 6.2).
3.14.13.1 U-bent tubes. When U-bent tubes are allowed (see 3.15.2, 3.16.1, 3.19.1, 3.20.1,
3.21.1), the minimum radius of the U-bend shall be 5/8 inch for 3/8 inch od tubes, 15/16 inch for
5/8 inch od tubes, and 1-1/8 inch for 3/4 inch od tubes.
3.14.13.l.1 Expansion of tubes. Tubes shall be expanded at each end into the tube sheets by
means of an automatic tube expander control and with tube expanders in accordance with
MIL-E-15809. The tube expander shall be adjusted so that expansion of the tube is stopped within
1/8 inch of the inner face of the tube sheet. In double tube sheet heat exchangers, the expansion
of the tubes in the inner tube sheet shall not start closer than 1/8 inch from the outer face of that
tube sheet and shall stop within 1/8 inch of the inner face. Care shall be taken that there is no
abrupt change in contour of the inner tube surface caused by the expanding operation. The
expander shall be set such that a wall reduction of approximately 10 percent is attained. .
3.14.14 Tube sheet drilling. The holes for 3/8 inch od tubes shall be reamed to 0.376 inch
diameter with a plus tolerance of 0.005 inch. The holes for 5/8 inch od tubes shall be reamed to
0.626 inch diameter with a plus tolerance of 0.005 inch- The holes for 3/4 inch od tubes shall be
reamed to 0.751 inch diameter with a plus tolerance of 0.005 inch. The holes for the inlet ends of
the tubes shall be flared on a radius of 5/16 inch for 3/8 inch od tubes, 1/2 inch for 5/8 inch od
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