segments (fig. 8-29) are placed around the two
of water pressure, so flooding is confined to the
carbon sealing rings, and the assembly is held in
one compartment only.
place by two garter springs. The two sealing discs
are installed with one on either side of the seal-
Stern Tube Seals
ing rings. Attached to each sealing disc are three
stops that mate with the slotted carbon segments.
The purpose of the stern tube seals is to pre-
These stops ensure that the sealing ring assembly
vent seawater from entering the ship at the point
does not rotate with the shaft.
where the shaft or shafts penetrate the hull.
Different types of stern tube seals are installed
When the compartment on one side of the seal
aboard ships, but they all serve the same purpose.
is flooded, water pressure on the carbon sealing
We will use the MX9 model installed on the
ring on the wet side creates a gap between the
DD-963 class ships as an example of a stern tube
carbon ring and sealing disc. This gap allows
water to enter the seal housing to force the other
The MX9 seal (fig. 8-30) is a radial face,
sealing ring against the shaft and sealing disc.
hydraulically balanced seal located on the inboard
Pressure on the far side sealing ring is directly
side of the ship's stern tube. Primary sealing
proportional to the head of water in the flooded
occurs between the stationary face insert and the
compartment plus the contact pressure of the
rotating seat in a plane perpendicular to the center
garter spring. Sealing action is a direct function
line of the shaft.
Figure 8-30.--MX9 stern tube seal.