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|  MIL-P-18526A(SH)
3 .3.9 Timing gears.
3.3.9.1 Timing gears where used shall be of the spur or double helical type. Gears
shall be fully enclosed and adequately lubricated. Timing gears shall be secured to the
shafts so as to prevent either radial or lateral movement.
3.3,9.2 Provision shall be made for replacement of timing gears in the field, so that
it will be satisfactory to carry and replace individual parts or rotating elements. The
method of installing and timing the timing gears shall be thoroughly explained, with sketches,
if necessary, in the technical manuals.
3.3.10 Mechanical shaft seals.
3.3.10.1 Pumps shall be equipped with mechanical shaft seals.
Magnetic type seals
shall not be used.
3.3.10.2 In addition to the requirement for mechanical shaft seals, pump shall have a
backup stuffing box to accommodate two or more rings of conventional or "soft" packing for
emergency use in the event of mechanical shaft seal failure. Packing shall be teflon im-
pregnated asbestos in accordance with MIL-P-24377.
3.3.10.3 Packing rings shall be inserted without removing the mechanical shaft seal.
3.3.10.4 Mechanical shaft seals shall be positioned on the shaft by means of stub or
step sleeves. Mechanical shaft seals shall not be positioned by use of set screws.
3.3.10.5 Positive liquid pressure shall be supplied to the seal faces under all condi-
tions of operation and there shall be adequate circulation of the liquid at the seal faces
to minimize the deposit of foreign matter on the seal parts. 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
drawing.
3.3.10.6 The design shall be such as to insure that if seal leakage occurs, fluid
cannot reach bearings or drive units. A fluid leakage collection reservoir with means for
adequate drainage to a safe point shall be provided to control any leakage that might occur.
3.3.11 Couplings
3.3.11.1 A flexible coupling of all-metal construction shall be installed between the
pump and the driving unit.
3.3.11.2 Flexible coupling pump hubs shall be keyed to the shafts and secured by lock
nuts . For pump shafts l-inch in diameter and larger the hubs shall he fitted on a taper
with keys.
3.3.11.3 Horizontal flexibly coupled units with bedplates shall have coupling guards
provided. Guards shall permit ready access to the coupling for lubrication and inspection.
3.3.12 Rubbing speeds.
3.3.12.1 Maximum rubbing speed in feet per minute (ft/min) for a particular class pump
shall be the speed established for the class pump during the qualification test. Pumps
shall not be offered or furnished on any contract or order which operate at a rubbing speed
greater than the rubbing speed at which the pump of the same class operated on qualification
test.
3.3.13 Threaded fasteners.
3.3.13.1 Threaded parts, such as bolts, studs, and nuts shall conform to Handbook H28.
The usc of tap bolts or cap screws is prohibited. Setting end of studs shall be class 5 fit,
or class 3 fit with locking resin, in accordance with MIL-S-22473. Nut end shall be class
3 fit.
Welding shall be in accordance with MIL-STD-270.
3.3.14
Welding
3.3.15 Painting.
3.3.15.1 External unmachined surfaces of ungalvanized ferrous metal parts shall be
thoroughly cleaned and coated with one coat of pretreatment conforming to MIL-P-15328, and
one coat of zinc chromate primer conforming to TT-P-645, followed by a finish coat of light
gray equipment enamel conforming to type I, class 2 of MIL-E-15090.
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