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|  MIL-P-17639F(SH)
seals shall be positioned on the shaft by means of stud or step sleeves on
close coupled pumps and step sleeves on flexible coupled pumps. Mechanical
shaft seals shall not be positioned by use of set screws. Pump certification
data shall contain certification by the seal manufacturer that there will be
adequate circulation of liquid and adequate lubrication at the seal faces when
the seal is installed as shown on the sectional assembly drawing.
3.3.8.8 Stuffing boxes of class C-2 pumps shall be cast integral with the
casing.
3.3.8.9 Pumps for submarine application shall be provided with pressure
breakdown device. The pressure breakdown device shall be located in way of a
shaft sleeve and not in way of the impeller. The device shall limit the leakage
to 5 gal/rein in the event of failure of the mechanical seal, under conditions
of maximum suction pressure specified.
3.3.8.9.1 Pumps shall be configured so that normal gland leakage, whether
from mechanical seal or when operating under emergency packing, shall be col-
lected and piped to waste. The collection area shall be tapped for drain con-
nections so that the leakage can be drained away from the pump casing foundation,
bearing housings, or driving units. With the pump running or shut down, the
collection area shall collect and drain all gland leakage, up to the greater
of either (a) 1 quart per minute or, (b) three times the minimum allowable
leakage rate recommended by the contractor and approved by the design review
agency for normal operation under packing.
3.3.9 Coupling.
3.3.9.1 For horizontal or vertical four-bearing units, an all-metal flexi-
ble coupling shall be installed between the pumps and driving units. Flexible
couplings for pumps for gasoline service or other explosive liquids shall be
non-sparking as specified (see 6.2.1). Flexible couplings shall be in accordance
with type II, class 2 of MIL-C-23233.
3.3.9.2 Flexible coupling pump hubs shall be keyed to the shafts and
secured by lock nuts. For pump shafts 1-1/2 inches in diameter and larger, the
hubs shall be fitted on a taper with keys parallel to the taper.
3.3.9.3 Rigid couplings shall have fitted bolts and the coupling flanges
shall be marked at assembly to insure proper reassembly after overhaul of the
unit.
3.3.9.4 Horizontal flexibly coupled units with bedplates shall have
coupling guards provided. Guards shall permit ready access to the coupling
for lubrication and examination.
3.3.10 Material. The materials of the pump shall conform to the materials
specified in table I. However, this specification is not intended to be restric-
tive provided proposed alternative materials will give equal or better service
than the material specified. Proposed alternative materials shall be subject
to approval by the design review agency. Components of the pump for which the
specific materials are not specified shall be materials best suited for the
intended service. Materials which can be sensitized and are subjected to heat
treatment in the sensitization range during fabrication shall be capable of
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