T-seals are used in applications where large
clearances could occur as a result of the expansion
of the thin-walled hydraulic cylinder. The T-ring
is installed under radial compression and provides
a positive seal at zero or low pressure. Backup
rings, one on each side, ride free of T-ring flanges
and the rod or cylinder wall (fig. 7-2, view B).
These clearances keep seal friction to a minimum
at low pressure. When pressure is applied (fig. 7-2,
view C), the T-ring acts to provide positive sealing
action as fluid pressure increases. One frequently
used T-ring, manufactured by Greene, Tweed and
Company, (called a G-Tring®1), incorporates a
unique, patented backup ring feature. One corner
on the ID of each radius-styled backup ring on
the G-Tring® set has been rounded to mate with
the inside corner of the rubber T. Figure 7-2, views
B and C, shows the G-Tring®.
There is no military standard part numbering
system by which T-seals can be identified. In
general, each manufacturer issues proprietary part
numbers to identify seals. However, it is common
practice to identify T-seal sizes by the same
dash numbers used for equivalent O-ring sizes
(discussed later in this chapter) as defined by
AS568 and MS28775 dimension standards.
Typically, an O-ring groove that accepts a certain
O-ring dash number will accept the same dash
number T-seal.
In the absence of an existing military standard
for identifying T-seals, a new and simple
1G-Tring® is a Greene, Tweed Trademark,
numbering system was created to identify T-seals
required for hydraulic actuators (piston seals only)
without reference to a particular manufacturer’s
part number. The Navy number is composed of
the letters G-T followed by a dash number of three
digits and one letter, R, S, or T (for example,
G-T-217T). The three digits are the appropriate
O-ring size dash number according to AS568 or
MS28775. The letters R, S, and T designate the
number of backup rings that the groove of the
T-seal is designed to accommodate: none, one,
or two, respectively.
V-RINGS
The V-ring is one of the most frequently used
dynamic seals in ship service although its
identification, installation, and performance are
probably most misunderstood. Properly selected
and installed, V-rings can provide excellent service
life; otherwise, problems associated with friction,
rod and seal wear, noise, and leakage can be
expected.
The V-ring is the part of the packing set that
does the sealing. It has a cross section resembling
the letter V, (fig. 7-3) from which its name is
derived. To achieve a seal, the V-ring must be
installed as part of a packing set or stack, which
includes one male adapter, one female adapter,
and several V-rings (fig. 7-4). The male adapter
is the first ring on the pressure end of the packing
stack and is flat on one side and wedge-shaped
on the other to contain the V of the adjacent
V-ring. The female adapter, the last ring of the
Figure 7-4.—Outside packed V-ring installations.
7-5
