John Bourne.

A Catechism of the Steam Engine online

. (page 26 of 34)
Online LibraryJohn BourneA Catechism of the Steam Engine → online text (page 26 of 34)
Font size
QR-code for this ebook

engines this weight is discarded, and two valves are used, which balance
one another. The framing consists of an upper and lower frame of cast iron,
bound together by eight malleable iron columns: upon the lower frame the
pillow blocks rest which carry the cylinder trunnions, and the condenser
and the bottom frame are cast in the same piece. The upper frame supports
the paddle shaft pillow blocks; and pieces are bolted on in continuation of
the upper frame to carry the paddle wheels, which are overhung from the

619. _Q._ - What are the dimensions and arrangement of the framing?

_A._ - The web, or base plate of the lower frame is 3/4 of an Inch thick,
and a cooming is earned all round the cylinder, leaving an opening of
sufficient size to permit the necessary oscillation. The cross section of
the upper frame is that of a hollow beam 6 inches deep, and about 3-1/2
inches wide, with holes at the sides to take out the core; and the
thickness of the metal is 13/16ths of an inch. Both the upper and the lower
frame is cast in a single piece, with the exception of the continuations of
the upper frame, which support the paddle wheels. An oval ring 3 inches
wide is formed in the upper frame, of sufficient size to permit the working
of the air pump crank; and from this ring feathers run to the ends of the
cross portions of the frame which supports the intermediate shaft journals.
The columns are 1-1/2 inches in diameter; they are provided with collars at
the lower ends, which rest upon bosses in the lower frame, and with collars
at the upper ends for supporting the upper frame; but the upper collars of
two of the corner columns are screwed on, so as to enable the columns to be
drawn up when it is required to get the cylinders out. The cross section of
the bottom frame is also of the form of a hollow beam, 7 inches deep,
except in the region of the condenser, where it is, of course, of a
different form. The depth of the boss for the reception of the columns is a
little more than 7 inches deep on the lower frame, and a little more than 6
inches deep on the upper frame; and the holes through them are so cored
out, that the columns only bear at the upper and lower edges of the hole,
instead of all through it - a formation by which the fitting of the columns
is facilitated.

620. _Q._ - What are the dimensions of the condenser?

_A._ - The condenser, which is cast upon the lower frame, consists of an
oval vessel 22-1/2 inches wide, by 2 feet 4-1/4 inches long, and 1 foot
10-1/2 inches deep; it stands 9 inches above the upper face of the bottom
frame, the rest projecting beneath it; and it is enlarged at the sides by
being carried beneath the trunnions.

621. _Q._ - What are the dimensions of the air pump?

_A._ - The air pump, which is set in the centre of the condenser, is 15-1/4
inches in diameter, and has a stroke of 11 inches. The foot valve is
situated in the bottom of the air pump, and its seat consists of a disc of
brass, in which there is a rectangular flap valve, opening upwards, but
rounded on one side to the circle of the pump, and so balanced as to enable
the valve to open with facility. The balance weight, which is formed of
brass cast in the same piece as the valve itself, operates as a stop, by
coming into contact with the disc which constitutes the bottom of the pump;
the disc being recessed opposite to the stop to enable the valve to open
sufficiently. This disc is bolted to the barrel of the pump by means of an
internal flange, and before it can be removed the pump must be lifted out
of its place. The air pump barrel is of brass to which is bolted a cast
iron mouth piece, with a port for carrying the water to the hot well;
within the hot well the delivery valve, which consists of a common flap
valve, is situated. The mouth piece and the air pump barrel are made tight
to the condenser, and to one another, by means of metallic joints carefully
scraped to a true surface, so that a little white or red lead interposed
makes an air tight joint. The air pump bucket is of brass, and the valve of
the bucket is of the common pot lid or spindle kind. The injection water
enters through a single cock in front of the condenser - the jet striking
against the barrel of the air pump. The air pump rod is maintained in its
vertical position by means of guides, the lower ends of which are bolted to
the mouth of the pump, and the upper to the oval in the top frame, within
which the air pump crank works; and the motion is communicated from this
crank to the pump rod by means of a short connected rod. The lower frame is
not set immediately below the top frame, but 2-1/2 inches behind it, and
the air pump and condenser are 2-1/2 inches nearer one edge of the lower
frame than the other.

622. _Q._ - What are the dimensions of the cylinder?

_A._ - The thickness of the metal of the cylinder is 9/16ths of an inch; the
depth of the belt of the cylinder is 9-1/2 inches, and its greatest
projection from the cylinder is 2-1/2 inches. The distance from the lower
edge of the belt to the bottom of the cylinder is 11-1/2 inches, and from
the upper edge of the belt to the top flange of the cylinder is 9 inches.
The trunnions are 7-1/4 inches diameter in the bearings, and 3-1/2 inches
in width; and the flanges to which the glands are attached for screwing in
the trunnion packings are 1-1/2 inch thick, and have 7/8ths of an inch of
projection. The width of the packing space round the trunnions is 5/8ths of
an inch, and the diameter of the pipe passing through the trunnion
4-5/8ths, which leaves 11/16ths for the thickness of the metal of the
bearing. Above and below each trunnion a feather runs from the edge of the
belt or bracket between 3 and 4 inches along the cylinder, for the sake of
additional support; and in large engines the feather is continued through
the interior of the belt, and cruciform feathers are added for the sake of
greater stiffness. The projection of the outer face of the trunnion flange
from the side of the cylinder is 6-1/2 inches; the thickness of the flange
round the mouth of the cylinder is 3/4 of an inch, and its projection 1-3/8
inch; the height of the cylinder stuffing box above the cylinder cover is
4-1/8 inches, and its external diameter 4-3/8 inches - the diameter of the
piston rod being 2-1/8 inches. The thickness of the stuffing box flange is
1-1/8 inch.

623. _Q._ - Will you describe the nature of the communication between the
cylinder and condenser?

_A._ - The pipe leading to the condenser from the cylinder is made somewhat
bell mouthed where it joins the condenser, and the gland for compressing
the packing is made of a larger internal diameter in every part except at
the point at which the pipe emerges from it, where it accurately fits the
pipe so as to enable the gland to squeeze the packing. By this construction
the gland may be drawn back without being jammed upon the enlarged part of
the pipe; and the enlargement of the pipe toward the condenser prevents the
air pump barrel from offering any impediment to the free egress of the
steam. The gland is made altogether in four pieces: the ring which presses
the packing is made distinct from the flange to which the bolts are
attached which force the gland against the packing, and both ring and
flange are made in two pieces, to enable them to be got over the pipe. The
ring is half checked in the direction of its depth, and is introduced
without any other support to keep the halves together, than what is
afforded by the interior of the stuffing box; and the flange is half
checked in the direction of its thickness, so that the bolts which press
down the ring by passing through this half-checked part, also keep the
segments of the flange together. The bottom of the trunnion packing space
is contracted to the diameter of the eduction pipe, so as to prevent the
packing from being squeezed into the jacket; but the eduction pipe does not
fit quite tight into this contracted part, but, while in close contact on
the lower side, has about 1/32nd of an inch of space between the top of the
pipe and the cylinder, so as to permit the trunnions to wear to that extent
without throwing a strain upon the pipe. The eduction pipe is attached to
the condenser by a flange joint, and the bolt holes are all made somewhat
oblong in the perpendicular direction, so as to permit the pipe to be
slightly lowered, should such an operation be rendered necessary by the
wear of the trunnion bearings; but in practice the wear of the trunnion
bearings is found to be so small as to be almost inappreciable.

624. _Q._ - Will you describe the valve and valve casing?

_A._ - The length of the valve casing is 16-1/2 inches, and its projection
from the cylinder is 3-1/2 inches at the top, 4-1/4 inches at the centre,
and 2-1/2 inches at the bottom, so that the back of the valve casing is not
made flat, but is formed in a curve. The width of the valve casing is 9
inches, but there is a portion of the depth of the belt 1-1/2 inch wider,
to permit the steam to enter from the belt into the casing. The valve
casing is attached to the cylinder by a metallic joint; the width of the
flange of this joint is 1-1/4 inch, the thickness of the flange on the
casing 1/2 inch, and the thickness of the flange on the cylinder 5/8ths of
an inch. The projection from the cylinder of the passage for carrying the
steam upwards, and downwards, from the valve to the top and bottom of the
cylinder, is 2-1/4 inches, and its width externally 8-5/8 inches. The valve
is of the ordinary three ported description, and both cylinder and valve
faces are of cast iron.

625. _Q._ - What description of piston is used?

_A._ - The piston is packed with hemp, but the junk ring is made of
malleable iron, as cast iron junk rings have been found liable to break:
there are four plugs screwed into the cylinder cover, which, when removed,
permit a box key to be introduced, to screw down the piston packing. The
screws in the junk ring are each provided with a small ratchet, cut in a
washer fixed upon the head, to prevent the screw from turning back; and the
number of clicks given by these ratchets, in tightening up the bolts,
enables the engineer to know when they have all been tightened equally. In
more recent engines, and especially in those of large size, Messrs. Penn
employ for the piston packing a single metallic ring with tongue piece and
indented plate behind the joint; and this ring is packed behind with hemp
squeezed by the junk ring as in ordinary hemp-packed pistons.

626. _Q._ - Will you describe the construction of the cap for connecting the
piston rod with the crank pin?

_A._ - The cap for attaching the piston rod to the crank pin, is formed
altogether of brass, which brass serves to form the bearing of the crank
pin. The external diameter of the socket by which this cap is attached to
the piston rod is 3-5/16 inches. The diameter of the crank pin is 3 inches,
and the length of the crank pin bearing 3-7/8 inches. The thickness of the
brass around the crank pin bearing is 1 inch, and the upper portion of the
brass is secured to the lower portion, by means of lugs, which are of such
a depth that the perpendicular section through the centre of the bearing
has a square outline measuring 7 inches in the horizontal direction, 3-7/8
inches from the centre of the pin to the level of the top of the lugs, and
2-1/2 inches from the centre of the pin to the level of the bottom of the
lugs. The width of the lugs is 2 inches, and the bolts passing through them
are 1-1/4 inch in diameter. The bolts are tapped into the lower portion of
the cap, and are fitted very accurately by scraping where they pass through
the upper portion, so as to act as steady pins in preventing the cover of
the crank pin bearing from being worked sideways by the alternate thrust on
each side. The distance between the centres of the bolts is 5 inches, and
in the centre of the cover, where the lugs, continued in the form of a web,
meet one another, an oil cup 1-5/8 inch in diameter, 1-1/8 inch high, and
provided with an internal pipe, is cast upon the cover, to contain oil for
the lubrication of the crank pin bearing. The depth of the cutter for
attaching the cap to the piston rod is 1-1/4 inch and its thickness is
3/8ths of an inch.

627. _Q._ - Will you describe the means by which the air pump rod is
connected with the crank which works the air pump?

[Illustration: Fig. 50. AIR PUMP CONNECTING ROD AND CROSS HEAD. Messrs.

_A._ - A similar cap to that of the piston rod attaches the air pump crank
to the connecting rod by which the air pump rod is moved, but in this
instance the diameter of the bearing is 5 inches, and the length of the
bearing is about 3 inches. The air pump connecting rod and cross head are
shown in perspective in fig. 50. The thickness of the brass encircling the
bearing of the shaft is three fourths of an inch upon the edge, and 1-1/8
inch in the centre, the back being slightly rounded; the width of the lugs
is 1-5/8 inch, and the depth of the lugs is 2 inches upon the upper brass,
and 2 inches upon the lower brass, making a total depth of 4 inches. The
diameter of the bolts passing through the lugs is 1 inch, and the bolts are
tapped into the lower brass, and accurately fitted into the upper one, so
as to act as steady pins, as in the previous instance. The lower eye of the
connecting rod is forked, so as to admit the eye of the air pump rod; and
the pin which connects the two together is prolonged into a cross head, as
shown in fig. 50. The ends of this cross head move in guides. The forked
end of the connecting rod is fixed upon the cross head by means of a
feather, so that the cross head partakes of the motion of the connecting
rod, and a cap, similar to that attached to the piston rod, is attached to
the air pump rod, for connecting it with the cross head. The diameter of
the air pump rod is 1-1/2 inch, the external diameter of the socket
encircling the rod is 2-1/8 inches, and the depth of the socket 4-1/2
inches from the centre of the cross head. The depth of the cutter for
attaching the socket to the rod is 1 inch, and its thickness 5/16 inch. The
breadth of the lugs is 1-3/8 inch, the depth 1-1/4 inch, making a total
depth of 2-1/2 inches; and the diameter of the bolts seven eighths of an
inch. The diameter of the cross head at the centre is 2 inches, the
thickness of each jaw around the bearing 1 inch, and the breadth of each
9/16 inch.

628. _Q._ - What are the dimensions of the crank shaft and cranks?

_A._ - The diameter of the intermediate shaft journal is 4-3/16 inches, and
of the paddle shaft journal 4-3/8 inches; the length of the journal in each
case is 5 inches. The diameter of the large eye of the crank is 7 inches,
and the diameter of the hole through it is 4-3/8 inches; the diameter of
the small eye of the crank is 5-1/4 inches, the diameter of the hole
through it being 3 inches. The depth of the large eye is 4-1/4 inches, and
of the small eye 3-3/4 inches; the breadth of the web is 4 inches at the
shaft end, and 3 inches at the pin end, and the thickness of the web is
2-5/8 inches. The width of the notch forming the crank in the intermediate
shaft for working the air pump is 3-1/2 inches, and the width of each of
the arms of this crank is 3-15/16 inches. Both the outer and inner corners
of the crank are chamfered away, until the square part of the crank meets
the round of the shaft. The method of securing the cranks pins into the
crank eyes of the intermediate shaft consists in the application of a nut
to the end of each pin, where it passes through the eye, the projecting end
of the pin being formed with a thread upon which the nut is screwed.

629. _Q._ - Will you describe the eccentric and eccentric rod?

[Illustration: Fig. 51. ECCENTRIC AND ROD. Messrs. Penn.]

_A._ - The eccentric and eccentric rod are shown in fig. 51. The eccentric
is put on the crank shaft in two halves, joined in the diameter of largest
eccentricity by means of a single bolt passing through lugs on the central
eye, and the back balance is made in a separate piece five eighths of an
inch thick, and is attached by means of two bolts, which also help to bind
the halves of the eccentric together. The eccentric strap is half an inch
thick, and 1-1/4 inch broad, and the flanges of the eccentric, within which
the strap works, are each three eighths of an inch thick. The eccentric rod
is attached to the eccentric hoop by means of two bolts passing through
lugs upon the rod, and tapped into a square boss upon the hoop; and pieces
of iron, of a greater or less thickness, are interposed between the
surfaces in setting the valve, to make the eccentric rod of the right
length. The eccentric rod is kept in gear by the push of a small horizontal
rod, attached to a vertical blade spring, and it is thrown out of gear by
means of the ordinary disengaging apparatus, which acts in opposition to
the spring, as, in cases where the eccentric rod is not vertical, it acts
in opposition to the gravity of the rod.

630. _Q._ - Will you explain in detail the construction of the valve
gearing, or such parts of it as are peculiar to the oscillating engine?

_A._ - The eccentric rod is attached by a pin, 1 inch in diameter, to an
open curved link or sector with a tail projecting upward and passing
through an eye to guide the link in a vertical motion. The link is formed
of iron case-hardened, and is 2-3/4 inches deep at the middle, and 2-3/8
inches deep at the ends, and 1 inch broad. The opening in the link, which
extends nearly its entire length, is 1-5/16 inch broad; and into this
opening a brass block 2 inches long is truly fitted, there being a hole
through the block 3/4 inch diameter, for the reception of the pin of the
valve shaft lever. The valve shaft is 1-3/4 inch diameter at the end next
the link or segment, and diminishes regularly to the other end, but its
cross section assumes the form of an octagon in its passage round the
cylinder, measuring mid-way 1-1/4 inch deep, by about 3/4 inch thick, and
the greatest depth of the finger for moving the valve is about 1 inch. The
depth of the lever for moving the valve shaft is 2 inches at the broad, and
1-1/4 inch at the narrow end. The internal breadth of the mortice in which
the valve finger moves is 5/16 inch, and its external depth is 1-3/4 inch,
which leaves three eighths of an inch as the thickness of metal round the
hole; and the breadth, measuring in the direction of the hole, is 1-1/2
inch. The valve rod is three fourths of an inch in diameter, and the
mortice is connected to the valve rod by a socket 1 inch long, and 1-1/8
inch diameter, through which a small cutter passes. A continuation of the
rod, eleven sixteenths of an inch diameter, passes upward from the mortice,
and works through an eye, which serves the purpose of a guide. In addition
to the guide afforded to the segment by the ascending tail, it is guided at
the ends upon the columns of the framing by means of thin semicircular
brasses, 4 inches deep, passing round the columns, and attached to the
segment by two 3/8 inch bolts at each end, passing through projecting
feathers upon the brasses and segment, three eighths of an inch in
thickness. The curvature of the segment is such as to correspond with the
arc swept from the centre of the trunnion to the centre of the valve lever
pin when the valve is at half stroke as a radius; and the operation of the
segment is to prevent the valve from being affected by the oscillation of
the cylinder, but the same action, would be obtained by the employment of a
smaller eccentric with more lead. In some engines the segment is not formed
in a single piece, but of two curved blades, with blocks interposed at the
ends, which may be filed down a little, to enable the sides of the slot to
be brought nearer, as the metal wears away.

631. _Q._ - What kind of plummer blocks are used for the paddle shaft

_A._ - The paddle shaft plummer blocks are altogether of brass, and are
formed in much the same manner as the cap of the piston rod, only that the
sole is flat, as in ordinary plummer blocks, and is fitted between
projecting lugs of the framing, to prevent side motion. In the bearings
fitted on this plan, however, the upper brass will generally acquire a good
deal of play after some amount of wear. The bolts are worked slack in the
holes, though accurately fitted at first; and it appears expedient,
therefore, either to make the bolts very large, and the sockets through
which they pass very deep, or to let one brass fit into the other.

632. _Q._ - How are the trunnion plummer blocks made?

_A._ - The trunnion plummer blocks are formed in the same manner as the
crank shaft plummer blocks; the nuts are kept from turning back by means of
a pinching screw passing through a stationary washer. It is not expedient
to cast the trunnion plummer blocks upon the lower frame, as is sometimes
done; for the cylinders, being pressed from the steam trunnions by the
steam, and drawn in the direction of the condenser by the vacuum, have a
continual tendency to approach one another; and as they wear slightly
toward midships, there would be no power of readjustment unless the plummer
blocks were movable. The flanges of the trunnions should always fit tight
against the plummer block sides, but there should be a little play sideways
at the necks of the trunnions, so that the cylinder may be enabled to
expand when heated, without throwing an undue strain upon the trunnion

633. _Q._ - What kind of paddle wheel is supplied with these oscillating

_A._ - The wheels are of the feathering kind, 9 feet 8 inches in diameter,
measuring to the edges of the floats; and there are 10 floats upon each
wheel, measuring 4 feet 6 inches long each, and 18-1/2 inches broad. There
are two sets of arms to the wheel, which converge to a cast iron centre,
formed like a short pipe with large flanges, to which the arms are affixed.
The diameter of the shaft, where the centre is put on, is 4-1/2 inches, the
external diameter of the pipe is 8 inches, and the diameter of the flanges
is 20 inches, and their thickness 1-1/4 inch. The flanges are 12 inches
asunder at the outer edge, and they partake of the converging direction of
the arms. The arms are 2-1/4 inches broad and half an inch thick; the heads
are made conical, and each is secured into a recess upon the side of the
flange by means of three bolts. The ring which connects together the arms,
runs round at a distance of 3 feet 6 inches from the centre, and the
projecting ends of the arms are bent backward the length of the lever which
moves the floats, and are made very wide and strong at the point where they
cross the ring, to which they are attached by four rivets. The feathering
action of the floats is accomplished by means of a pin fixed to the
interior of the paddle box, set 3 inches in advance of the centre of the
shaft, and in the same horizontal line. This pin is encircled by a cast
iron collar, to which rods are attached 1-3/8 inch diameter in the centre,
proceeding to the levers, 7 inches long, fixed on the back of the floats in
the line of the outer arms. One of these rods, however, is formed of nearly
the same dimensions as one of the arms of the wheel, and is called the
driving arm, as it causes the cast iron collar to turn round with the
revolution of the wheel, and this collar, by means of its attachments to
the floats, accomplishes the feathering action. The eccentricity in this
wheel is not sufficient to keep the floats in the vertical position, but in
the position between the vertical and the radial. The diameter of the pins
upon which the floats turn is 1-3/8 inch, and between the pins and paddle
ring two stud rods are set between each of the projecting ends of the arms,
so as to prevent the two sets of arms from being forced nearer or further
apart; and thus prevent the ends of the arms from hindering the action of
the floats, by being accidentally jammed upon the sides of the joints.
Stays, crossing one another, proceed from the inner flange of the centre to
the outer ring of the wheel, and from the outer flange of the centre to the
inner ring of the wheel, with the view of obtaining greater stiffness. The
floats are formed of plate iron, and the whole of the joints and joint pins
are steeled, or formed of steel. For sea-going vessels the most approved
practice is to make the joint pins of brass, and also to bush the eyes of
the joints with brass; and the surface should be large to diminish wear.

634. _Q._ - Can you give the dimensions of any other oscillating engines?

Online LibraryJohn BourneA Catechism of the Steam Engine → online text (page 26 of 34)