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Stuffing boxes and mechanical shaft seals |
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|  MIL-P-18472G(SH)
3.3.7.2 Rotor assembly.
Barrel-type pumps shall be so constructed that the
assembled pump rotor exclusive of the coupling, plus non-rotating parts which can
only be installed by removing some rotating parts, can be removed, replaced and
stored as a complete assembly. This assembly shall be able to pass through a
hatch of the specified diameter (see 6.2).
3.3.8 Stuffing boxes and mechanical shaft seals. Mechanical shaft seals
may be used for waste heat boiler feed and waste heat boiler circulating pumps.
A separate source of clean cooling water shall be provided to the mechanical
seal for both services. The contractor shall be responsible to the design
review agent or installing activity of the cooling requirements.
3.3.8.1 Separators. A cyclone separator is required for each stuffing box.
The separator shall be integrally mounted on the pump (preferably by means of a
bracket on the casing parting flange) and shall be connected to the suction and
discharge piping by means of tubing and fittings.
Each seal installed shall be provided with a
3.3.8.2 Seal materials.
solid gland plate that houses two or more rings of packing for use in the event
of a mechanical seal failure. The gland shall be such that the packing can be
installed without removing the mechanical shaft seal. The gland shall also be
provided with a flush connection to ensure that positive liquid pressure is
supplied to the seal faces under all operating conditions and that there is
adequate circulation of the liquid at the seal faces to minimize deposits of
foreign matter in the seal parts.
3.3.8.3 Seal mater ials. Metal seal internal parts for waste heat boiler
pumps shall be constructed of nickel-copper or highly alloyed corrosion-
resisting steel in accordance with ASTM A 744, grade CN-7M or CN-7MS. Metal
seal internal parts for fresh water service pumps shall be constructed of type
304 or 316 corrosion-resisting steel or nickel-copper alloy or highly alloyed
corrosion-resisting steel in accordance with ASTM A 744, grade CN-7M or CN-7MS.
The mechanical shaft seal shall have a solid tungsten carbide or silicon carbide
against carbon sealing surface.
3.3.8.4 Cyclon e separator construction. Cyclone separators shall be
constructed of nickel-copper alloy. Fittings for abrasive separators and pump
casings shall be of the straight thread type adapter with O-ring seals and shall
be constructed of nickel-copper alloy. Tubing shall be copper-nickel (70-30) in
accordance with MIL-T-16420.
3.3.8.5 Glands. Stuffing box glands shall be set up by nuts threaded on
studs secured in the casings. The emergency packing gland shall be set up by
nuts threaded on studs. Space shall be provided between bearing and stuffing
boxes to permit easy examination of mechanical seals and bearings. Mechanical
shaft seals shall be positioned on the shaft by means of stub 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.
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