Improvements in or connected with Steam Generators.
Year: 1897

page_text: Date of Application, 11th Mar., 1897-Accepted, 12th June, 1897
Improvements in or connected with Steam Generators.
We, JACQUES AUGUSTIN NORMAND, FRANÇOISE ELISABETH NORMAND,
and MARIE EMILIE NORMAND, all of the Firm of La Société Augustin
Normand, et Cie. of 67 Rue du Perrey, Le Havre, in the Republic of France,
Engineers, do hereby declare the nature of this invention and in what manner the
same is to he performed to be particularly described and ascertained in and by
the following statement :-
The sub-division into two, or more, parts of the total boiler power employed in
feeding an engine with steam, offers the advantage, that any damage that may be
sustained by either of the component boilers does not entail a stoppage of the
engine while, on the other hand, such subdivision is attended with the incon-
venience, that it makes it difficult for the feed to be equally divided, whenever
combustion becomes very active. This drawback is particularly serious in the case
of boilers constructed to hold but a small volume of water, and subjected to
intense heating; the use of which boilers is becoming more general, principally for
marine purposes.
But little reliance can be placed upon the readings of the water gauges in those
cases because of the violent ebullition of the water, or of the currents of water, due
to the rapidity of circulation.
In ships where one engine is supplied with steam by a number of boilers of the
class referred to, the heating invariably proves to be less active than where one
such boiler is employed, and the weight is of course considerably greater.
Where, however, a single boiler is used,-with surface-condensation,―little
notice is taken of the water-gauge readings; and provided the engineer has means.
for ascertaining that no water is lost through the accidental discharge pipe of the
hot-well, or otherwise, this fact is sufficient to satisfy him that the supply of water
in the boiler is as required.
The object of this invention is to combine the safety, which is incidental to the
use of two, or more, component boilers, with the uniformity in the feed-water
supply, which is incidental to single boilers.
As against the various types of feed-water regulators at present in use, the
improved arrangement according to this invention presents the double advantage of
comprising no moving mechanism and of enabling the feeding to be kept up to a
normal level by means of simpler appliances than are required where donkey-
engines are adopted; in addition to which the arrangements according to this
invention are not so expensive as, and are more economical of steam than, donkey-
engines. And furthermore the arrangement which forms the subject of this
invention is more consistent with the use of feed-water heaters which are of course
desirable on account of the saving they effect in the consumption of fuel.
This invention mainly consists in connecting the component boilers by two pipes,
or systems of tubing, provided with valves, one of which pipes, or systems of
tubing, puts the steam reservoirs of the boilers in communication with each other;
the sectional area being sufficient, to reduce the difference of pressure between the
apparatus to but a few centimetres of water,-even whilst the firing is at its
highest, whilst the other pipe, or system of tubing, makes connection between the
water contained in both boilers; the lower part of this pipe or system of tubing,
being situated at the lowest water-level compatible with the satisfactory working
of the boiler.

page_text: The diameter of the second pipe, or system of tubing, should be sufficient for
fully feeding one of the boilers when the whole supply of feed-water has been
introduced into the other; and that, too, without there being any difference of
pressure between the two boilers. For land boilers, there is no limit to the
diameter beyond that which is the outcome of the size of the cut-off valves, but
for marine boilers, it is desirable that such diameter should not be large enough to
cause the lowering of the water-level in the boilers to a dangerously great extent
owing to the movements of the vessel.
The accompanying drawings illustrate the manner in which this invention may
be carried out on board a torpedo boat, having two boilers from which its other
applications will also be understood. The example chosen is one that presents the
greatest difficulties, as in vessels of this class, the disturbances of the level,
occasioned by the speed of the vessel, are considerable, while the boilers are erected
at a considerable distance apart.
Figures 1 and 2 are elevations at right angles to each other and Figure 3, is
a plan.
A is the rear-boiler, and A', the forward boiler, both of which boilers are
supposed to be of the Normand type having one common stoke-hold.
XX is a horizontal line when the vessel is not in motion. X'X' is a horizontal
line, when the vessel has attained her maximum speed;
YY indicates the water-level in the rear boiler A, when the vessel is at rest;
Y'Y' indicates the water-level in the said boiler when the vessel is at maximum
speed;
ZZ and ZZ are the corresponding water-levels in the forward boiler A',
Band are the steam valves of the two boilers, respectively, ani
(and
are the steam supply pipes of the respective boilers;
D is the collecting pipe which conducts the steam obtained from the two boilers
to the one engine;
E E' are feed pipes ; and
Fis the pipe connecting the water contained in the two boilers in the vicinity of
the water levels; the said pipe being provided with cocks, or valves, G G'.
The diameter of the pipes C C is the same as that of the collecting pipe D,
although each of the pipes C C₁ is intended to deliver only one half of the steam
passing through the said pipe D. The pipes C C₁ fulfil a double function as they
cause the steam to pass from the boiler wherein the pressure may be higher to the
boiler in which a lower pressure may prevail; while at the same time they each
deliver about one half of the total amount of steam used by the engine. By
slightly increasing the diameter of the pipes C C and their valves B B', the
employment of a special connection for restoring uniformity of pressure between
the two boilers is rendered unnecessary; pipe-joints and intermediate valves are
done away with; and the rapid disconnection of one boiler from the other, in case
of emergency, is facilitated.
It is important, where the main steam-pipes serve to establish equality of pressure
in the two boilers, that such pipes should be kept open at all times when the engine
is running, and provision should be made that the valves of the said main steam-
pipes do not close automatically, under the pressure due to the flow of steam.
The throttling of the steam, where it is deemed necessary for saving fuel, should
be effected at such a part of the piping as will enable the said throttling to be
performed without any reduction of the sectional area of the steam-connection
between the boilers.
Were it necessary for the communication between the boilers to have a greater
cross sectional area than that of the collector D, in order to restore equality of
pressure between the two boilere, it is preferable to do this rather than to make a
separate connection between the two steam spaces.
The feed-water may be admitted either into the steam space, or at about the
lowest level consistent with satisfactory working, or even at any level within the
water contained in the boiler.

page_text: The first mentioned arrangement is calculated to render the water circulation
more active and, consequently, the consumption of fuel more economical; but
owing to possible irregularities in the feed-water supply, which at one time may be
excessive, and at another may fail, or be insufficient, corresponding irregularities in
the pressure of boiler may also arise,-and attain, a considerable inagnitude,—and
as feeding at the lowest level is apt, accidentally, to lead to the same inconveniences
as feeding into the steam space, and as delivery of the feed-water into the water in
the boilers is free from this drawback and, as regularity of pressure is one of the
main desiderata for obtaining constant levels in coupled boilers, the adinission of
the feed-water under the water level of the boilers is to be preferred.
In ordinary boilers, the operation of sending the feed water into the water
contained in the boilers through tubing common to more than one boiler is attended
with the great danger that if the valves of the governors should remain in the
raised position, and if there happen to be an appreciable difference of pressure
between the boilers owing to the steam inlet valves not being sufficiently opened,
or from any other cause, the boiler wherein the pressure is higher might discharge
its water into the boiler wherein the pressure is lower, up to the level of the feed.
This danger is obviated by the addition of the pipe F, remaining constantly
open whilst the boilers are in normal operation, and situated on a level, or approxi-
mately on a level, with the surface of the water in the boilers. The duty which
this pipe discharges, the feed-collector could not perform, even though it were
placed on a level otherwise conducive to such purpose, for two reasons, viz.:-
firstly, because of the cut-off valves in the feed-pipes of each boiler, which
destroy the free connection between the boilers; and secondly, by reason of the
considerable variations of pressure existing between the several points of the feed-
collector.
At all events it is important that emergency feeding, from the reserved tanks,
should always be directed into the water, instead of into the steam.
I will now shew that the laws which govern the delivery of steam and water
enable in this arrangement the three necessary conditions to be complied with in
practice as follows:-
(1.) The diameters of the pipes connecting the steam spaces should be sufficient
to reduce the difference of pressure between the two boilers to but a few centimetres
of water-say from five to ten centimetres.
(2.) Where this difference of pressure is nil, the diameter of the pipe situated in
the vicinity of the water levels should be sufficient to furnish the required supply
of feed-water to one boiler, whilst the other boiler may have the benefit of a full
supply.
(3) The diameter of the said pipe should not be large enough to allow of the
water-level being lowered to a dangerous extent in one boiler, and unduly raised in
the other at the same time, so as to create priming, whilst the vessel is pitching and
tossing, or rolling.
It is hardly necessary to repeat that there is no occasion for the fulfilment of the
third condition, in the case of land boilers to which this invention may be equally
applied.
Let us suppose the dimensions and other data of the apparatus represented in
the drawings to be as follows:-
Surface of grate
2
square metres.
100 do. do.
Heating surface
Pressure above the vacuum
15 atmospheres.
Vaporisation of water per hour while }
✓ ✓ 4.500 kilogrammes.
working at maximum power
Diameter of opening through valves B
and B¹ and internal diameter of pipes C }
⚫16 metres.

page_text: Diameter of passage through the con-
necting valve G and internal diameter
of the pipe F, the lower part of which
is situated on the lowest water level in
the boilers consistent with satisfactory
•10 metres.
Working
In calculating the speed of the steam-discharge, I will take the formula embodying
the old theory, which is more accurate in its results than the thermo-dynamic
theory. The old formula, as given by Pochet ("Nouvelle Mécanique Industrielle "
page 277) is as follows:-
4
8 × 00000307
40750 = 202 metres.
Zeuner's table (Pochet, page 404) gives 223 metres, but the velocities contained
in that table are well known to be too high.
The most unfavourable condition of things, for the equalisation of pressures, is
when the total quantity of steam generated in one boiler (this total in the present
4500 kilogrammes
1.25 kilogrammes per second) is compelled to
example being
3600 seconds
=
pass through the other boiler, instead of being conveyed almost in its entirety
directly to the engine.
This would happen if the steam spares were connected by a special pipe
- 16 centimetres in diameter, quite apart from the steam inlet pipes, and if, while the
engine was in full operation, the attendant omitted to open the main steam valve of
one of the boilers.
Let the weight of a cubic metre of steam at 15 atmospheres' pressure be
7.68 kilogrammes; if it be supposed that, in consequence of the resistances
occurring, the real speed W' is only of the theoretical speed W, then we shall
Gnd W to be expressed thus

page_text: Therefore the difference of pressure, in metres of water, is
p- po = '00045 × 155 metres = .070 metres.
Thus the maximum difference of pressure between the two boilers will be
7 centimetres of water.
The 16 centimetre diameter of the connecting steam pipes will be amply
sufficient as the pipe F will to a certain degree assist in equalising the pressures.
Let us now see to what level it will be necessary for the water to rise, to cause one
of the boilers to be supplied with its share of feed-water through the pipe F,
on the assumption that the total supply has been introduced into the other
boiler.
We will suppose that delivery takes place through one half of the sectional area
of the ning only that is to now.
corresponding to a depth of fall of 11 millimetres.
Let us now calculate how much water may pass from one boiler to the other
while the vessel is pitching.
Assuming the time occupied by each single
oscillation to be -
The maximum angle of motion
-
-
1.5 seconds
-
10°
-
-
4.50 metres
The evaporating surface of each boiler
-
-
.74 metres x 2.30 metres =
1.70 metres square.
The distance between the centres of the water
surfaces of the two boilers
->
The difference of level corresponding to the maximum amplitude of the angle of
oscillation is
4.50 metres x sin. 10° = ⚫78 metres.
We will assume that the discharge during the space of 1.5 seconds of one single
scillation is the same as that which would, in the same period of time, be caused
þy a constant fall of ·50 metres.
•

page_text: The quantity of water passing from one boiler to the other (it being observed
that the flow of water would occupy the full sectional area of the pipe) will be:—
II
2
2.00
025 bin matuos
x 015040 metres.
1.5 seconds
This figure, again, is of no importance, inasmuch as the firing is in that
case far less artive than it is in torpedo boats, and therefore the sectional area
of the pipe might be considerably reduced in relation to the steam evaporative
surface.
Within the separating tank, sea breakers, in nearly water-tight, may be so
dispel as reluce the vitudinal movements of the water. and also,
consequently, the difference of level hetween the two boilers occurring during one
longitudinal inclination of the vessel.
As the heating surfaces, in pitching, are uncovered, or exposed, but for a short
time, these surfaces can in no case rise to a high temperature. It is well known,
moreover, that there exist, boilers, such as Thornycroft's boilers, wherein the
upper parts of the heating tubes normally rise above the water-level.
A moveable device, adapted to partially close the pipe F, during the rocking
movements of the ship, may be provided so as to reduce the quantity of water
passing at the time, from one boiler to the other. This arrangement, however,
does not appear to be free from danger. It is important that the curve formed in
the said pipe F as a provision for the effects of expansion should lie in a horizontal
plane, so that the said pipe may serve for the passage of both steam and water.
The curved steam pipes CC' and water pipe F may be replaced by straight pipes
with expansion joints.
Thus it will be scen that in the example selected, the three conditions which I
have assumed to be essential are fulfilled in such a manner as to render the working
of a pair of coupled boilers quite reliable. In this instance the torpedo boat
steaming at full speed lifts forward so as to take a longitudinal inclination of
about 3 centimetres per metre, and the distance between the centres of the
evaporative surfaces of both boilers is :
⚫03 metres x 4.50 metres = 135 metres.
It follows that the rear boiler is erected about 10 metres higher than the
forward boiler, a situation which is most unfavourable to the coupling together of
such boilers.
The arrangement would, however, be far less inconvenient if the two boilers
were inverted and the single stoke-hold replaced by two stoke-holds; in which
case the distance between the centres of the steam-evaporative surfaces would be
far less.
The various practical difficulties existing in the example here adduced are

page_text: such that as the invention can be applied to this, the coupling of two, or
more, boilers, feeding one single engine, will be possible in most cases, by the
same means.
This invention is still more readily applicable to torpedo destroyers, in which
steam is generally supplied to each engine by two boilers, because, in vessels of
that class, the changes of level occasioned by the speed of motion is less than in
torpedo boats proper. It may form an advantageous substitute for the very
delicate automatic governors hitherto employed, many of which are inaccessible by
reason of their being situated within the boilers. The excessive activity with
which firing is carried on in ships of this description readers the employment of
perfectly reliable self-operating governors absolutely necessary.
This invention may besides be applied to any number of boilers greater than
two, sny, to a battery of boilers such as is met with in works on land or on board
ships of high power as it will enable the feed-water to be equally divided, or
distributed, between boilers displaying very great aggregate power.
Thus in a large ship, one of Normand Sigaudy's boilers of medium size may
supply steam sufficient for developing 2000 horse power with moderate firing owing
to the peculiar construction of the boiler, wherein every square metre of the grate
is made to burn from 160 to 180 kilogrammes per hour, provided the engine be of
a sufficiently economical construction. Three such boilers, therefore, would
develope 6000 horse power, and a twin screw vessel each engine of which is
driven by the three boilers would thus be capable of indicating 12000 horse power,.
without requiring any feed regulator other than that according to this invention.
The erection will present no difficulty, if the boilers be arranged athwart-ship
with a longitudinal heating-chamber extending on both sides of the vessel such an
arrangement being particularly convenient for the supply of coals to the stokers as
well as for coupling the boilers.
Each of the Normand-Sigaudy double ended boilers could be replaced by two
Normand's single boilers, coupled according to this invention. It will be seen by
this example how this invention may be used for dividing equally between six
boilers, giving steam to a single engine, the feed-water furnished by a common
feed-water pipe.
In this case, as well as in the case of a battery of land boilers, the pipe
connecting the several boilers at the level of the water should consist of a collector
provided with branch pipes leading to each boiler, so that either of the boilers can
at any time, be isolated from the rest of the battery without interruption in the
connection between the remaining boilers. The same arrangement should be used
for the steam collector which serves moreover to ensure equality of pressure in the
several boilers. The movements in the direction of the ship's length are the only
ones that are not permanent. Transversely, ships are apt to assume and retain
either permanently, or at all events for lengthy periods of time, au inclined
position under the pressure of the wind, or the thrust of the waves, or in
consequence of a want of symmetry in the distribution of loads; or again during a
gyratory movement of somewhat long duration in which certain vessels are apt to
heel considerably to one side. Besides, the duration and amplitude of the trans-
verse oscillations are always greater than those of the lungitudinal movements.
The boilers should therefore preferably be connected into a battery longitudinally.
Where transverse coupling must needs be resorted to, it will be necessary to
increase the steam-spaces of the boilers, lest variations in the level should produce
dangerous priming.
But in the case of longitudinal coupling also a slight increase in the dimensions
of the steam-spaces will be found to be of advantage; at all events, whatever
inconveniences may arise therefrom, they will be less serious than those involved in,
separate and distinct feeding, which would be, felt whenever the firing began to be
conducted with increased activity.
From the foregoing description it will readily be seen why the lower portions of
the valves in the pipe F have to be arranged in the vicinity of the lowest water

page_text: level. Were they placed higher, the said pipe would not feed the boiler which is
wanting in water, unless the water in the overfed boiler rose to such a height as
to bring about a dangerous fall of the water level in the other biler. If the said
pipe were placed lower, whenever one of the main steam-boiler valves happened to
be insufficiently opened, or in the event of all the said valves not being
simultaneously closed when the engines are stopped, a difference of pressure
between the two boilers might occasion a descent of the water level in one boiler,
so as to endanger the heating surfaces; while in the other boiler there would occur
an undue rise of the water level, apt to produce priming in re-starting.
Too low a position of the pipe would also be attended with the inconvenience
that, should a leak of some magnitude occur in one of the boilers, requiring the
immediate severance of the same, the remaining boiler, or boilers, would lose an
appreciable quantity of water before the damaged boiler could be isolated.
Under normal conditions, the cocks GG of the pipe should constantly remain
open and only be closed in case of any accident rendering oue of the boilers
unserviceable.
They should be operated at frequent intervals in order to ascertain whether they
are in proper working order.
This invention may be applied to boilers of all types, or systems; and the
proportions and dimensions of the main parts thereof, as well as its accessory
arrangements, may be varied to suit various requirements, without departure from
the leading principle of the invention.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :—
1. Two, or more, boilers furnishing steam to a single engine coupled together as
herein before described so that the feed-water is equally distributed among such
boilers, and a proper water level maintained in each; the means of connection
consisting, in addition to the connection between the steam spaces,―of a connecting
pipe the lower portion of which is situated at, or near, the lowest water level
consistent with the satisfactory working of the boilers.
2. A steam generator arranged as herein before described and represented in the
accompanying drawings.
Dated this 11th day of March 1897.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.