the “rising main,” by the nearest or most convenient route to above
the level of the cold-water cistern, and terminates either by being
carried through the roof (as shown) or by being turned over the top
of the cistern referred to (as shown in dotted lines). This pipe,
when the apparatus is in use, is charged with water to a little above
the level of the cold water in the cistern, and the pipe is open at
the top end to admit of the free escape of steam, and on that account
is sometimes called the expansion pipe; from this pipe is, or should
be carried _all_ the draw-off services to the various points at which
they are required. In event of this rising main being carried to a
considerable distance or height, it should be “returned” from any
convenient point below the cold cistern (as shown in dotted lines at
_d_); this will cause the water to circulate in this upper service
and avoid the annoyance and waste caused by drawing sometimes a
large quantity of cold water (which lies stagnant in single pipes)
before the hot water is obtained. When this “return” is effected, the
service is known as the “secondary flow and return.”
[Illustration: 129. Hot-water System (Old Form).]
Another good use to which the return can be put is in event of any
draw-off services being unusually long, as that shown at _m_ to the
dressing-room in the illustration, the return can be connected as
shown in dotted lines, and will bring about the same good results as
explained in “returning” the rising main.
The supply of cold water to the apparatus is either brought by a
direct and distinct service from the cistern, or is branched from the
nearest existing cold service, but in the latter case the existing
service must be of good size, for reasons that will be explained
later on. The cold supply should be provided with a stop tap _f_,
which is found most convenient if placed near the cylinder, as
it can then be used by workmen or others without their having to
traverse the house, but this tap should have a loose key or handle,
which should be kept by some responsible person to prevent its being
interfered with by any one ignorant of its use. There should be also
a tap provided at a convenient point, say _g_, to empty the cylinder
when the boiler requires to be cleaned or any repairs effected, and
this tap should have a loose key for the reasons before stated.
The chief advantage of this system is safety, the cook or user being
unable to empty the cylinder, consequently should the water supply
fail, the fire can be lighted in the usual way without risk, as in
ordinary use it would take several days to boil away or evaporate the
contents of the cylinder and boiler.
Another advantage gained by this system is that the cylinder being
in such a warm situation, much less heat is lost by radiation, and
by its being nearer to the boiler the circulation is effected more
rapidly; and there are several other minor advantages to be gained
by it, which, however, are not of sufficient importance to warrant
detail here. The cold supply pipe _h_ leads from the cistern _i_ to
the cylinder _k_; _l_ is the boiler; _m_ are draw-off service pipes
with taps _n_ in the various apartments where needed.
Fig. 129 is commonly known as the “high” or the “old” system. This
consists of a square or rectangular tank _a_, which performs the
function of a reservoir for the hot water in the same way as a
cylinder, but instead of being situated near the boiler _b_, it is
fixed somewhere above the highest draw-off service, but of course
below the cold cistern _c_; it is commonly found in the roof or attic
in proximity to the cistern, but these are cold and bad situations
for it; it is more often found in the bathroom, enclosed in a casing
or cupboard, which is thereby made an efficient airing closet, and
serves somewhat to prevent loss of heat referred to before (and
hereafter), and the presence of the tank in the bathroom, although
occupying considerable space, is a source of warmth, no mean
advantage in winter.
The tank _a_ is connected with the boiler _b_ by “flow” and “return”
pipes _d e_, the same as the cylinder, but they are necessarily
much longer; the draw-off services _f_ are, or should be, _all_
connected to the “flow” pipe _d_ as shown, as the water in this pipe
is the first to become heated as the water circulates or “flows”
from the boiler to the tank; and an expansion pipe _g_ (not called a
rising main in this instance) is carried from the highest point in
the tank _a_ to above the level of the cold supply _c_, as in the
cylinder system. There is no need to return this expansion pipe,
but an unusually long draw-off service can and should be returned
for the reasons before explained, and the method is to connect and
carry the draw-off service from the flow pipe in the usual way and
return it into the return pipe at a lower point, somewhat after the
manner shown at _h_. Obviously the run or course of all pipes has to
be adapted to circumstances, but it can be taken as an invariable
rule that in correctly executed work “flow” pipes never descend and
“return” pipes never ascend, but this will be more fully explained
later on. In speaking of circulating pipes, the “flow” is recognised
as running from boiler to tank (or cylinder), and the “return” from
tank to boiler.
The cold-water supply _i_ is carried and connected to the tank _a_
in the same manner as to a cylinder, and provided with a stop tap
_k_ to save the necessity of plugging the pipe where it leaves the
cold-water cistern.
The chief advantage of this system is obtaining hot water a little
quicker (but in less quantity) from the time the fire is lighted,
than in the cylinder system, as it can be drawn almost immediately
it leaves the boiler; but as good results in this respect can be
attained with the cylinder if the directions subsequently given
are attended to; another advantage in this system is that it can
be erected at less expense than the other, and the tank costs but
little more than half the price of a cylinder. These advantages are
more than counterbalanced by the disadvantages, viz. the easy means
of exhausting the apparatus of water if the supply fails, the longer
period occupied in obtaining a body of hot water, and the necessarily
cold or cool situations of the tank and pipes, so causing loss of
heat by radiation, &c.
A few lines may be here devoted to explaining the cause of
circulation, which the generality of householders are totally
unacquainted with. For the reader to fully understand the subject,
he must first know that water is composed of extremely minute
particles (molecules), quite invisible to the eye, which have the
property of gliding over, under, around, to and from each other,
as circumstances dictate, in we may say a perfectly free manner,
almost entirely without friction or resistance. When the apparatus
is charged and the fire lighted, the particles nearest the fire
become heated and expanded, and are, bulk for bulk, rendered lighter
than their fellows, and consequently rise to the top of the boiler;
finding an outlet there they rise up into this, and continue to
rise until they reach the highest limit, which in No. 2 system is
the top of the tank, and in No. 1 system, the top of the cylinder,
unless the rising main is “returned,” in which case it will be where
this “return” commences. Immediately the expanded particles leave
the heated surface of the boiler, other cold particles descend into
their place and are heated and expand to follow their predecessors,
and so it continues as long as there is heat applied to the boiler.
The circulation is really a continuous stream of expanded (heated)
particles of water ascending the flow pipe, and a corresponding
stream of cold or cooler particles descending the return pipe, a
natural and very simple means of automatically transporting the hot
water from the heating chamber (boiler) to the reservoir (tank) and
automatically providing a supply of cold water to be heated in its
turn.
The specific gravity of water at the boiling point, compared with
water at the freezing point, is as 21 to 20, i.e. 20 gal. of very
cold water will balance 21 gal. of very hot water.
The following are the few general rules to be observed for the
efficient, economic, and safe working of either description of
apparatus.
Commencing at the boiler, it is very necessary that the flue under
this be quite cleared of cinders and ash once daily, and the length
of the flue should be ascertained, as they differ considerably, and
many instances occur where these flues are scrupulously cleaned
but only in half or three-fourths their length, and very quickly
the accumulation at the end of the flue becomes hard and solid,
and an inexperienced person would then consider it to be the wall
which forms the boundary at the back of these flues; this stoppage
of course effectually prevents the water heating as it should do.
Another cause of the water failing to heat quickly is omitting
to have the interior of the boiler cleared of the incrustation
or deposit (commonly known as fur) that accumulates more or less
according to circumstances that will be fully described later
on; when this inner coating attains a moderate thickness it very
naturally retards the heat in passing from the fire to the water,
especially as it is a poor conductor. There is, however, a more
important reason why this incrustation should be removed regularly,
and that is, when the boiler is coated to a certain thickness (which
coating is more or less porous according to the district) it prevents
the water coming in contact with the iron, and the boiler plate,
however thick, is soon destroyed the same as if it contained no water
at all, or to use a more familiar illustration, the same as a kettle
would be “burnt” if left on the fire without having any water in it;
this is a serious result from the costly nature of the repair.
The general form of incrustation is caused by the lime or chalk
(bicarbonate of lime generally) held in solution, being separated
from the water and precipitated; this precipitation commences at a
moderately low temperature and gradually increases as the temperature
rises, and the whole (excepting a very small quantity) is deposited
when the water boils. The incrustation varies very much in quantity
according to the district, as before stated; it is generally what
is known as hard water that has the greatest percentage of this
depositable matter; in some favoured districts the water is so soft
that no appreciable deposit occurs, whilst in others it is not safe
to leave the boiler longer than a month without cleansing to keep it
in good order. There is also a variation according to whether the
water boils much or otherwise, therefore the only reliable plan is to
have a good workman in after a certain period, and he can then decide
whether the amount of incrustation is too great or whether it might
be permitted to go longer, and how long.
With London water, boilers that are in ordinary daily use should be
cleaned out every 6 months to keep them in really good order, but to
avoid the trouble of remembering dates, &c., many good firms keep a
register for this work.
The most important places in the boiler that need cleaning are the
parts immediately where the fire plays, especially the angles, where
the boiler plates are welded or joined--and careless workmen are apt
to neglect these parts--as the deposit is very hard and stone-like at
these places.
It may be said without exaggeration that three-fourths of the
fractures that occur to wrought-iron boilers are due to excessive
incrustation, i.e. want of regular cleaning or removal of deposit.
Incrustation does not occur (but to an extremely small extent) in
boilers used for heating purposes only, as in this instance the
same water is heated over and over again, and water only contains a
certain quantity of lime in solution, which is all deposited when it
first boils.
It might be mentioned that in some places the deposit is organic
matter, and is found in the boiler much resembling a layer of mud; in
such instances the water should be filtered for obvious reasons.
The tank, cylinder and pipes, and in fact the whole apparatus
(excepting the boiler) will be rendered more efficient by being
covered with some non-conducting material to prevent loss of heat
by radiation. Radiation is an important feature occasionally, as
very many instances are known of apparatus being a complete failure,
solely by reason of the tank or pipes (or both) being in very cold
situations (cold draughty roofs, stone passages, &c., &c.); and a
moment’s reflection shows that loss of heat is really loss of fuel
attended with certain inconveniences well known to many who are
suffering with this trouble. The common non-conducting material
used is felt in its various forms. Hair felt is the best, as will
be readily understood, and can be obtained at many ironmongers and
may be applied by any one; for pipes it should be cut and put on
in strips, wound round spirally, and tied. Another method is to
encase the tank and pipes and pack the casing with a non-conducting
material, such as cow hair, slag wool, sawdust, &c., but it is _most
necessary_ that the casing be packed, otherwise the heated pipes
will render the casing a flue which will draw in cold air and very
materially assist in cooling the water, especially if the casing has
open or badly fitted ends, in which case failure of the apparatus can
be confidently anticipated.
In addition to the heat-saving properties, this covering also
possesses the advantages of keeping the different places cool (an
advantage for certain seasons only, excepting the kitchen) and saves
the pipes from attack of frost, and under ordinary circumstances,
if a small fire is left at night with the boiler flue _closed_,
moderately warm water can be had for bathing _before the fire is
lighted in the morning_; these two latter advantages are perhaps the
greatest.
In reference to this subject, it is a great convenience if the range
(if the boiler is in a range) is provided with a means of opening
the fire, as, with an open fire a small quantity of fuel can be
placed on it the last thing at night and it will burn in safety
for a considerable time, and really _hot_ water can by this means
be obtained at an early hour in the morning if the apparatus is
“insulated” as explained above.
If the felt is placed round the pipes and tank without casing it
should be one or two layers thick, say about ½ in., so that the hand
can scarcely perceive any heat when the apparatus is in full action;
a single layer of felt will answer, but not so perfectly.
Boiler explosions are at all times most serious disasters, for not
only is the damage very great, but if any living thing is moderately
near at the time the result is almost certain to be fatal, and it is
a much-regretted fact that three-fourths or nearly all the terrible
accidents of this kind could have been avoided with ordinary care;
the reason that this form of accident is so serious is that before
the explosion takes place, the steam has to attain sufficient power
to burst the boiler, which is from ¼ to ½ inch thick of wrought iron,
compared to which the human body is a frail object, and suffers
accordingly.
The causes of explosions at present known are, firstly, stoppage
in both the circulating pipes, caused by frost or by the terrible
practice of putting stop taps in these pipes, which prevents escape
of steam generated in the boiler, and steam _must_ and _will_ escape
if it bursts the boiler to effect its release.
Secondly, failure of water supply. This is sometimes caused by a
hidden or unnoticed leakage, or in country residences where the water
is pumped this failure is not an uncommon thing (but only rarely
results in an accident). If the want of water is unnoticed for a
time, the boiler will empty itself by evaporation and afterwards
become red hot; should the water then run in, steam will be generated
so rapidly that the pipe outlets will not be sufficient for its free
escape, and the boiler bursts; all this happens in much less time
than is occupied in explaining it, in fact so quick that there is
no time for escape if any one is unfortunately near; this, however,
under ordinary circumstances cannot occur with the No. 1 system.
There is another though rare cause of accident (which, however,
once came under the writer’s notice) that may occur with either
system, and that is the ends of the circulating pipes nearest the
boiler becoming stopped by incrustation; this incrustation, as has
been before explained, takes place in the greater proportion of
boilers, and also to a less extent in the pipes, especially near the
boiler, and in course of time the pipes will both become completely
stopped, but the reason that accidents from this cause are rare
is that abundant notice is given by the steam making a variety of
unpleasant noises and sometimes violent shaking, in forcing its way
through the partly closed pipes, but this noise must not always be
confounded with the sounds produced when pipes are imperfectly run or
“trapped” and contain air, but whenever noises are heard a practical
man should be consulted at the earliest convenience, and if a tap
is opened and no water should flow, after it has been open say one
minute, the fire should be immediately extinguished and kept so until
the reason of failure of water is discovered and remedied. No alarm
need be experienced at the rumbling noise to be heard when the water
is boiling, but this water has no need and should not be permitted
to boil; when the noise is heard, 4 or 5 gal. should be drawn off,
this will be replaced in the tank or cylinder by the same quantity
of cold water, and the temperature will be reduced; the damper which
regulates the boiler flue should be out only when the water is cool
and requires rapid heating; even then it must not be pulled out so
far that the flame, &c., roars as it passes under the boiler, as the
boiler will not experience the full benefit of the heat.
It has been suggested by some authorities that to prevent the water
in pipes becoming frozen (this may be considered the most likely
cause of explosion) a tap or taps should be left a little open at
night so that the water is kept in motion; this, however, cannot
be relied upon in a really severe frost, and it is also a waste
of water, which is a consideration where the supply is by manual
power, &c. Another method suggested is to empty the whole apparatus
every frosty night; this is a very good plan to save damage to pipes
as well as prevent accidents, but there is the doubt that but few
would care to practise this on account of the trouble, and there is
a serious risk if it is forgotten to turn the water on until after
the fire is lighted. Tolerable reliance can be put on felting or
casing the pipes, but the most efficient remedy is to see that the
boiler is fitted with a safety valve, which, as the name betokens,
is a source of safety and most probably of comfort also; if it is
not convenient to attach a safety valve direct into the boiler, it
should be connected by a short length of pipe, which however is a
weakness, as the pipe may eventually be stopped by incrustation, and
on that account it should be of good size and should be cleared,
if necessary, every time the boiler is opened for cleaning. Safety
valves should always be fixed in sight so that they can be tested
whenever desired. The working principle of a spring safety valve
(which has general preference just now) is, firstly, a brass
sealing which closes the opening leading to the boiler and is held
in position by a spring and central pin, and the whole works in a
strong brass case which is perforated with several good-sized holes;
when the valve is fixed, the workman can and does set the spring
(generally by a screw-down cap at top) so that it withstands about
3 or 4 lb. more pressure than the boiler is subjected to by the
pressure of water; when by any reason an undue pressure is exerted
inside the boiler it causes the seating to rise, and the steam and
some water escape into the brass case and through the holes above
referred to, and the boiler is relieved. The noise occasioned by this
escape is _very_ plainly heard, and notice is thus drawn, but the
fire need not be extinguished.
It would be a desirable feature if every boiler fixed (except open
ones) was provided with a valve, as it is purchasing freedom from
risk at a low price (a few shillings only).
There is a common cause of complaint and annoyance in having at
some taps to draw off a quantity of cold water that lies stagnant
in the service pipe before the hot water can be obtained from the
circulation; this is caused by the draw-off service being a long and
single pipe, and can be only remedied by “returning” it something
after the manner shown in the illustrations, and so cause the water
to circulate along it; this trouble is not only a source of annoyance
but a practical loss also, as for every quantity of hot water drawn a
certain quantity is left in the service to get cold, and this happens
every time the tap is used, excepting such taps as are in constant
use, and the water only remains stationary 2 or 3 minutes, but this
in domestic purposes only applies to the scullery service at certain
hours in the day.
It may have come to many people’s notice that when some lever-handle
taps are shut a noise and jarring in the pipe ensues; this is caused
by the sudden stoppage of the flow of water when the pressure is
considerable; when the vertical pressure is say 50 or 60 ft. (height
of cistern above the tap) and the tap is opened, the water rushes out
and gains a strong momentum; by turning the handle or lever of the
tap the stoppage is so sudden that a shock is sustained almost the
same as an object falling from a height being suddenly stopped by
coming in contact with the ground; this concussion and noise is not
only unpleasant but does harm, which is quickly noticeable with light
lead pipe, which is either stretched or has protuberances formed upon
it, and a continuance of the shocks or really blows will then cause
it to split; it will be therefore commonly found that screw-down taps
are used with lead pipe where any pressure exists, and the screw-down
tap would meet with more favour but for an objectionable feature,
which is the number of times it has to be screwed or unscrewed to
shut and open it; but there are now made screw-down taps that open
or shut with one turn, and these no doubt will come into more general
use if found practically good and when the patent expires.
Retarded circulations arise from a variety of causes, amongst which
may be mentioned incapacity of the boiler for the work, caused by
the boiler not having sufficient heating surface; this is shown by
the whole apparatus becoming fully charged with hot water late in
the day after several hours firing; the only remedy is to reduce
the work the boiler has to do or change the boiler itself. Another
cause is by pipes being dipped or trapped. The flow pipe having
an inclination or dip downwards, which causes the circulation to
become air-locked, this causes noises in the pipes and shakings
as the steam is passing or trying to expel the air; this air is
eventually expelled, but occurs again when the apparatus is emptied
and recharged in boiler cleaning, repairing, &c.; to remedy this the
pipes must be traced up and the defect so discovered. Another cause
is by incrustation in the pipes; this can be noticed by its gradual
growth, also incrustation in boiler, but if boiler is kept clear as
referred to earlier in the chapter, the pipes will keep in very fair
order. The only remedy for furred pipes is to take them out and by
heating and striking to dislodge the deposit; this costs as much
almost as renewing the service; with care in regular cleaning it will
not occur. Obstructions either stationary or floating are sometimes
found in the pipes and retard circulation; these are generally caused
by the workmen failing to look through the tubes before fixing them,
or the obstruction may be in the form of sediment in rural districts,
&c.; the only efficient remedy that can be suggested is to engage
the services of an experienced hot-water fitter in any of the cases
mentioned, as it lies beyond the power of the householder to remedy
them.
[Illustration: 130. Flow Pipe.]