[Illustration: FIG. 50.]
In fig. 50 is shown a gland and stuffing-box for the piston rod of a
vertical engine. A B is the piston rod, C D a portion of the cylinder
cover, and E F the _stuffing-box_. Fitting into the bottom of the
stuffing-box is a brass bush H. The space K around the rod A B is filled
with _packing_, of which there is a variety of kinds, the simplest
being greased hempen rope. The packing is compressed by screwing down
the cast-iron gland L M, which is lined with a brass bush N. In this
case the gland is screwed down by means of three stud-bolts P, which are
screwed into a flange cast on the stuffing-box. Surrounding the rod on
the top of the gland there is a recess R for holding the lubricant.
[Illustration: FIG. 51.]
[Illustration: FIG. 52.]
The object of the gland and stuffing-box is to allow the piston rod to
move backwards and forwards freely without any leakage of steam.
Fig. 51 shows a gland and stuffing-box for a horizontal rod. The
essential difference between this example and the last is in the mode of
lubrication. The gland flange has cast within it an oil-box which is
covered by a lid; this lid is kept shut or open by the action of a small
spring as shown. A piece of cotton wick (not shown in the figure) has
one end trailing in the oil in the oil-box, while the other is carried
over and passed down the hole A B. The wick acts as a siphon, and drops
the oil gradually on to the rod. In this example only two bolts are used
for screwing in the gland; and the flanges of the gland and stuffing-box
are not circular, but oval-shaped.
In the case of small rods the gland is made entirely of brass, and no
liner is then necessary. Fig. 52 shows a form of gland and stuffing-box
sometimes used for small rods. The stuffing-box is screwed externally,
and carries a nut A B which moves the gland.
EXERCISE 51: _Gland and Stuffing-box for a Vertical Rod._--Draw the
views shown in fig. 50 to the dimensions given. Scale 6 inches to a
foot.
EXERCISE 52: _Gland and Stuffing-box for a Horizontal Rod._--Fig.
51 shows a plan, half in section, and an elevation half of which is
a section through the gland flange. Draw these to a scale of 6
inches to a foot, using the dimensions marked in the figure.
EXERCISE 53: _Screwed Gland and Stuffing-box._--Draw, full size,
the views shown in fig. 52 to the given dimensions.
A more elaborate form of gland and stuffing-box is shown in fig. 53.
This is for a large marine engine with inverted cylinders, such as is
used on board large ocean steamers. The stuffing-box is cast separate
from the cylinder cover to which it is afterwards bolted. The lubricant
is first introduced to the oil-boxes marked A, from which it passes to
the recess B, where it comes in contact with the piston rod. To prevent
the lubricant from being wasted by running down the rod, the main gland
is provided with a shallow gland and stuffing-box which is filled with
soft cotton packing, which soaks up the lubricant.
The main gland is screwed up by means of six bolts, and to prevent the
gland from locking itself in the stuffing-box, it is necessary that the
nuts should be turned together. This is done in a simple and ingenious
manner. One-half of each nut is provided with teeth, and these gear with
a toothed wheel which has a rim only; this rim is held up by a ring C.
When one nut is turned, all the rest follow in the same direction.
[Illustration: FIG. 53.]
EXERCISE 54: _Gland and Stuffing-box for Piston Rod of Large
Inverted Cylinder Engine._--The lower view in fig. 53 is a half
plan looking upwards, and a half section of the gland looking
downwards. The upper view is a vertical section. Complete all these
views and add an elevation. Scale 3 inches to a foot.
_Note._--The large nuts, the wheel, the supporting ring, and small
gland are made of brass.
_Dimensions of Stuffing-boxes and Glands._
_d_ = diameter of rod. _t__{1} = thickness of
_d__{1} = diameter of box (inside). stuffing-box flange.
_l_ = length of stuffing-box _t__{2} = thickness of gland
bush. flange.
_l__{1} = length of packing space. _t__{3} = thickness of bushes in
_l__{2} = length of gland. box and gland.
_t_ = thickness of metal in _d__{2} = diameter of gland bolts.
stuffing-box. _n_ = number of bolts.
+----------------------------------------------------------+
| _d_ | _d__{1} | _l_ | _l__{1} | _l__{2} | _t_ | _t__{1} |
+-----+---------+-----+---------+---------+------+---------+
|1 | 1-3/4 | 3/4| 2 | 1-1/2 | 7/16| 1/2 |
|1-1/2| 2-1/2 |1-1/4| 2-5/8 | 2 | 9/16| 11/16 |
|2 | 3-1/2 |1-3/4| 3-1/4 | 2-1/2 | 11/16| 7/8 |
|2-1/2| 4-1/8 |2-1/4| 3-7/8 | 2-7/8 | 13/16| 1-1/16 |
|3 | 4-3/4 |2-3/4| 4-1/2 | 3-1/4 | 15/16| 1-1/4 |
|3-1/2| 5-1/4 | 3 | 5-1/8 | 3-5/8 |1 | 1-3/8 |
|4 | 5-7/8 |3-1/4| 5-3/4 | 4 |1 | 1-3/8 |
|4-1/2| 6-3/8 |3-1/2| 6-3/8 | 4-3/8 |1-1/16| 1-9/16 |
|5 | 7 |3-3/4| 7 | 4-5/8 |1-1/16| 1-9/16 |
|6 | 8 |4-1/4| 8-1/4 | 5 |1-1/8 | 1-11/16 |
+----------------------------------------------------------+
+-------------------------------------------------+
| _d_ | _t__{2} | _t__{3} | _d__{2} | _n_ |
+-----+-----------------+---------+---------+-----+
|1 | _t__{2}=_t_ | 3/16 | 7/16 | 2 |
|1-1/2| when gland | 1/4 | 5/8 | 2 |
|2 | flange is | 5/16 | 3/4 | 2 |
|2-1/2| made of cast | 5/16 | 7/8 | 2 |
|3 | iron and | 3/8 | 1 | 2 |
|3-1/2| _t__{2}=_t__{1} | 3/8 | 1 | 2 |
|4 | when gland | 7/16 | 1 | 2 |
|4-1/2| flange is | 7/16 | 7/8 | 4 |
|5 | made of | 7/16 | 1 | 4 |
|6 | brass. | 1/2 | 1-1/4 | 4 |
+-------------------------------------------------+
The proportions of glands and stuffing-boxes vary considerably but the
above table represents average practice.
EXERCISE 55:--Make the necessary working drawings for a gland and
stuffing-box for a locomotive engine piston rod 2-1/2 inches in
diameter, to the dimensions given in the table.