Chapter VI: The Atmospheric System (2)

The state of things which existed when this discovery was made in effect involved the renewal of the valve the whole distance from Exeter to Newton; so that, as the cost of the valve was 1,160_l._ per mile, an immediate outlay of some 25,000_l._ became essential to the maintenance of the system, and this at the time when the real difficulties of the valve question had become most apparent. By galvanising the iron plates of the valve the mutually destructive action of the iron and the leather might have been prevented; but a remedy was also required for the other serious defect which leather, as the material of the valve, was found to exhibit, namely, its tendency to become permeable to air after long-continued use under air-pressure, owing to the inward escape of the material with which it had been dressed.

These difficulties were not only such as had not been anticipated, but such as no one was justified in anticipating.

* * * * *

It now became necessary for Mr. Brunel to consider what course, under the circumstances, it was most advisable for the Company to adopt.

A Committee of the Board was appointed to examine the whole question; and, at their desire, Mr. Brunel made a report upon it, which was as follows:--

August 19, 1848.

You have called upon me to report to you upon the present state of
the Atmospheric apparatus, and particularly upon the circumstances
connected with the partial destruction of the longitudinal valve
which has lately occurred, and the probability of remedying this
serious defect, and of keeping the valve in repair and in good
working order.

Such a report involves necessarily the consideration of the whole
question of our experience of the working of the Atmospheric
System; because, to arrive at any clear appreciation of the present
state of the apparatus, I must refer to the circumstances which
have affected our working up to the present time, and particularly
to the several difficulties which we have had to encounter and
their effects.

The first difficulty, and one which was as unexpected as it was
serious, was in the working of our stationary engines. Upon the
efficiency of these machines must of course ultimately depend the
economy and efficiency of the working of the whole system, however
perfect in itself might be the Atmospheric apparatus. Accordingly,
great precautions were taken--precautions which I still think such
as to justify the expectation that we should secure the best
engines that could be made.

The three first manufacturers of the day were employed--Messrs.
Maudslay (who had had some experience in this particular branch,
having made the engines for the Croydon railway), Messrs. Boulton
and Watts, and Messrs. Rennie. They prepared their own designs; and
I know that they each bestowed much thought in the preparation of
these designs, and took considerable interest in the results.

Mr. Samuda, a man of considerable mechanical abilities, having all
the experience that could be had upon the subject, and deeply
interested in the success of the engines, was also employed to
superintend their manufacture.

Notwithstanding all these precautions, notwithstanding excellent
workmanship, these engines have not, on the whole, proved
successful; none of them have as yet worked very economically, and
some are very extravagant in the consumption of fuel, burning
nearly double the quantity of others, while the average is very
considerably more than it ought to be.

The apparent causes of this excess are various in the different
engines, but all resulting more or less apparently from the want of
experience in this particular application of power, and from the
circumstance of the form of the engines being somewhat novel, and
involving slight differences in the proportion and arrangement of
the parts; and the consumption of steam being greater than was
calculated upon, it has been obtained by a more wasteful
expenditure of fuel, and the evil has been aggravated.

The difficulty of remedying this state of things has been increased
by the consequence of defects in the Atmospheric apparatus, which,
causing a much greater demand upon the working of the engines, has
delayed, or has entirely prevented, our throwing an engine out of
work, to introduce the requisite improvements.

Still, so far as this defect in the engines is concerned, there is
no doubt that it is susceptible of considerable, if not complete
remedy, and that a reduction of one-third may be effected in the
consumption of fuel.

In the Atmospheric apparatus itself our difficulties have been more
numerous.

We have suffered from extreme cold, particularly when it followed
quickly upon wet.

We have suffered from extreme heat, and also from heavy falls of
rain. These difficulties have in turn been encountered and
gradually overcome, and I think the effects of all these causes
upon a valve in good condition may now be obviated, if not
entirely, yet so much so as to render their operation unimportant.

The same remedy applies to all three--keeping the leather of the
valve oiled and varnished, and rendering it impervious to the
water, which otherwise soaks through it in wet weather, or which
freezes in it in cold, rendering it too stiff to shut down; and the
same precaution prevents the leather being dried up and shrivelled
by the heat; for this, and not the melting of the composition, is
the principal inconvenience resulting from heat. A little water
spread on the valve from a tank in the piston-carriage has also
been found to be useful in very dry weather, showing that the
dryness, and not the heat, was the cause of leakage; but a new
difficulty has arisen, and a new defect has been discovered, one
much more serious in its extent and its possible consequences, and
one which renders the operation of each of the previously mentioned
causes of difficulty much more powerful and mischievous.

Within the last few months, but more particularly during the dry
weather of last May and June, a considerable extent of longitudinal
valve failed by the tearing of the leather, at the joints between
the plates; the leather first partially cracked at these points,
which causes a considerable leakage, particularly in dry weather;
after a time it tears completely through, and that part of the
valve is destroyed, and requires to be replaced.

A considerable extent has thus been replaced, but the whole of the
valve is more or less defective from this cause; the amount of
leakage is considerable, and the working altogether inefficient. I
have examined carefully portions of the valve that have been
removed, and I find that at the part which has given way the
texture of the leather seems to be destroyed--it is black, and has
evidently been acted upon by the iron of the plates.

Upon some parts of the line the injury seems to be more general
than upon others; but it is very difficult to examine the valve in
place, so as to form any correct opinion of the extent of the evil.

As regards the cause of this defect, Mr. Samuda, who under his
contract is at present liable for the repair of the valve, urges
that the valve was kept for a length of time in cases after it was
delivered to the Company, and that, exposed to damp, and the oil
in the leather not being renewed on the surface, the iron may have
rusted, and the leather have been injured; and he refers to
instances lately observed, in which valves taken out of the top of
a case which had been exposed to wet do show similar signs of
injury.

Supposing, however, this assumption to be correct, it would not
seem to affect the question of his liability. He suggests also, as
a cause, that the valve remained for a length of time in place
without been used and even worked over by locomotive engines, which
prevented its being properly oiled and attended to; that the evil
has been aggravated by an attempt to reduce too much the use of oil
to the leather; and, lastly, that the piston-gear has been allowed
to get out of adjustment, so that the leather of the valve has been
strained.

I shall not, however, here enter into the discussion of this
question of liability, but confine myself to the consideration of
the evil, and the possibility of remedying it.

Of the extent of the evil, for the reason I have given, it is
impossible to form any accurate opinion; it is impossible,
therefore, to say that it does not extend more or less over the
whole distance, excepting, of course, that which has been already
replaced. That which is injured cannot be repaired in place, but
must be removed, and the remedy can only be applied in the new
valve.

It is quite possible that a valve made in the same manner as the
present, if properly attended to from the first, and with our
present experience, might not be subject to this destruction, and
Mr. Samuda states that such is the case at Dalkey; but I do not
think that I could rely upon this result. By painting, but, better
still, by zincing or galvanising the iron plates, and making them
overlap a short distance, both the chemical and the mechanical
action of the plate upon the leather appears to be prevented, and I
believe, therefore, that this evil may be remedied at a small
increased cost in any new or repaired valve that might be laid
down: but of the existing valve I can say no more than I have done.
It is not now in good working condition, and I see no immediate
prospect of its being rendered so.

From the foregoing observations, it will be evident that I cannot
consider the result of our experience of the working between Exeter
and Newton such as to induce one to recommend the extension of the
system.

I believe that if the longitudinal valve were restored, the working
expenses might be immensely reduced; that the quantity of fuel
consumed which is the great item of expense, may be diminished by
one-third; that the price of the fuel, which now costs 18s. per ton
at the engine-houses, ought to be reduced at least 12 per cent.;
and that the total cost may thus be brought down to a moderate
amount, such as I had originally calculated upon. But the cost of
construction has far exceeded our expectations, and the
difficulties of working a system so totally different from that to
which everybody, traveller as well as workmen, is accustomed, have
proved too great; and therefore, although, no doubt, after some
further trial, great reductions may be effected in the cost of
working the portion now laid, I cannot anticipate the possibility
of any inducement to continue the system beyond Newton.

With respect to the future working of the apparatus between Exeter
and Newton, I feel in great difficulty as to expressing any
opinion, seeing that a very large expense has been incurred, and
believing, as I do, that the cost of working may be so very much
reduced; but that reduction can only be effected by the almost
entire renewal of the valve, and by some expenditure in the
engines. And unless Mr. Samuda or the patentees undertake the
first, and extend considerably the period during which they would
maintain it in repair, and unless they can offer some guarantee for
the efficiency of that valve, I fear that the Company would not be
justified in taking that upon themselves, or incurring the expense
attending the alteration of the engines.

I believe that for the inclined planes, as an assistant power, the
apparatus will be found applicable and efficient; and as the
engines and the pipes are nearly ready at Dainton, it may be found
desirable to try it there, provided a satisfactory arrangement can
be entered into for the maintenance and efficiency of the valve.

I have not referred to our great disappointment in not obtaining
the assistance of the telegraph in the working of the engines, and
the greatly increased consumption of coal consequent upon the
working the engines unnecessarily, because this evil is now nearly
removed; but some further reductions may still be made by using the
telegraph by night as well as day, which has not yet been in our
power to do, but which I trust will be commenced this week.

The Committee to whom this report was made, and who had been also in constant communication with Mr. Brunel, placed the result of their investigation before the Board. The Directors, after carefully considering the information given them, reported as follows:--

Your Directors, without pronouncing any judgment as to the ultimate
success of the Atmospheric System, and while they are prepared to
afford to the patentees and other parties interested in it the use
of their machinery for continuing their own experiments, have
arrived at the conclusion, with the entire concurrence and on the
recommendation of Mr. Brunel, that it is expedient for them to
suspend the use of the Atmospheric System until the same shall be
made efficient at the expense of the patentees and Mr. Samuda.

At the meeting in August, the proprietors adopted the Directors’ report, and the line was worked throughout by locomotives on and after September 9.

In the following November Mr. Thomas Gill, the chairman of the Board of Directors, published an ‘Address to the Proprietors,’ in which he strongly deprecated the abandonment of the Atmospheric System, and proposed that the Company should embark on a further experiment. Mr. Gill’s pamphlet was referred to three of the Directors, Mr. Thomas Woollcombe, Mr. Charles Russell, and Mr. James Wentworth Buller. With Mr. Brunel’s assistance, and to a great extent from memoranda written by him, they prepared a statement which went very fully into all the points raised by Mr. Gill.

After combating Mr. Gill’s propositions, they observe:--

Of the two men who are most deeply concerned in the further trial
of any reasonable experiment to perfect the Atmospheric System, we
find that one, Mr. Brunel, disapproves of the proposal for the
purpose as insufficient and unsatisfactory; the other, Mr. Samuda,
had not sufficient confidence in the result, or in Mr. Gill’s
estimates for its accomplishment, to offer the only security which
would justify the Company in endeavouring to effect it.

In conclusion they express an opinion that the suspension of the Atmospheric System in the previous September was a prudent and necessary step, and that nothing had since occurred to justify its resumption.

The proprietors adopted the view taken by the Committee, and no further attempt was made to work the railway on the Atmospheric System.

Under these circumstances, it cannot be a matter of surprise that Mr. Brunel was much censured for having advised the South Devon Railway Company to work their line on the Atmospheric System.

The reasons which led him to recommend the use of the Atmospheric System on the South Devon, and the causes of its failure, have been very fully described, and it has been also shown that the most important of these were the defects of the pumping-engines, and the deterioration of the longitudinal valve.

When the formidable character of these difficulties had fully declared itself, the South Devon Railway Company were not in a position to spend any more money upon a system which, as the event had proved, was, in one of its most important details, still in the experimental stage.

There can be no doubt that the abandonment of the Atmospheric System was the wisest step which, under the circumstances, could be adopted; and it was recommended to the Directors by Mr. Brunel with a simple and self-sacrificing disregard of every consideration except that which was always paramount with him, the interests of those by whom he was employed.[72]

NOTE (p. 143).

_Comparison of Stationary and Locomotive Power._

In order clearly to set forth the reasons which justify the statement made by Mr. Brunel,[73] that stationary power if freed from the weight and friction of any medium of communication, such as a rope, must be cheaper than locomotive power, it is desirable to consider, (1) the waste of power which arises from the locomotive having to move itself as well as the train; and (2) the excess of cost at which a given power was supplied by a locomotive, as compared with that at which it could have been supplied by a stationary engine.

On the first point, the best information can be obtained from experiments made by Mr. Daniel Gooch during the gauge controversy. The results are very suitable for use in the present investigation, as the South Devon was to be a broad-gauge railway. Moreover, as the broad-gauge engine with which these experiments were tried was one of a class more powerful for their weight not only than the contemporary narrow-gauge engine, but also than the engines Mr. Brunel had experience of when he wrote his report three years previously, the results may be considered to represent very favourably the then existing case for the locomotives.

The engine employed in the experiments weighed, with its tender, about fifty tons. The maximum power it was capable of delivering by the pressure of steam in its cylinders was represented as a tractive force of 4,900 lbs. at a speed of 60 miles an hour, equivalent to 784 indicated horse-power; and at 40 miles an hour 5,200 lbs., equivalent to 555 indicated horse-power.

It is next to be considered how this power would, when running at the speeds mentioned, be employed in overcoming the elements of resistance. These are:--

(1) The working friction of the machinery.

(2) The rolling resistance of the engine and tender.

(3) The air resistance due to the engine frontage.

(4) The rolling resistance of the train.

(5) The air resistance on the portion of the train unprotected by the tender.

(6) The resistance due to gradient.

The following symbols and quantities may be conveniently made use of to denote the various terms of the equation between force and resistance.

Total available tractive force in lbs. F

Weight of engine and tender (superfluous load) in tons 50

Weight of train (useful load) in tons W

The sum of the resistances of machinery, rolling resistance, and air resistance of engine and tender R

Rolling resistance of train in lbs. per ton K

Gradient G

Speed in miles per hour V

Resistance of air (according to the received empirical formula)

1
= --- (frontage area) × V^{2}
400

Frontage area of train in square feet 63

Frontage area of portion of train unprotected by the tender, in square feet 24

For a locomotive train therefore
24
F = R + WK + --- V^{2} + (50 + W) 2240 G.
400

For a system that dispenses with the locomotive

63
Tractive force = WK + --- V^{2} + W 2240 G.
400
Therefore

W (K + 2240 G) + ·1575 V^{2}

= the useful tractive force, and

R + 112000 G - ·0975 V^{2}

= the tractive force wasted by the use of the locomotive.

Therefore

F={R + 112000 G-·0975 V^{2}} + {W (K + 2240 G) +·1575 V^{2}}

and the useful load

(F- R - 112000 G - ·06 V^{2})
W = -----------------------------
K + 2240 G.

The values which Mr. Gooch’s experiments give for the two selected speeds are as follows[74]:--

+---------------+---------+-----------------+----------+
|Miles per Hour | R (lbs.)| K (lbs. per ton)| F (lbs.) |
+---------------+---------+-----------------+----------+
| 40 | 1500 | 12·5 | 5200 |
| 60 | 2100 | 18·6 | 4900 |
+---------------+---------+-----------------+----------+

Using these values, the results in the following table are obtained, being the conditions appropriate to the two speeds at successive ascending gradients:--

+------+---------+-------+-------+------+-------+------+------+-----------+
|Miles |Ascending|Useful |Super- | Gross|Useful |Waste |Gross |Ratio of |
|per |Gradient |Load | fluous| |Load |Horse-|Horse-|Horse-power|
|Hour | |in tons|Load in| |in tons| power| power|Waste to |
| | | | tons | | | | |Useful |
| | | | | | | | |Horse-power|
+------+---------+-------+-------+------+-------+------+------+-----------+
| {| 0 | 288 | 50 | 338 | 411 | 144 | 555 | ·35 |
| {| 1/200 | 128 | 50 | 178 | 352 | 203 | 555 | ·58 |
| {| 1/100 | 71 | 50 | 121 | 292 | 263 | 555 | ·90 |
| 40 {| 1/75 | 50 | 50 | 100 | 252 | 303 | 555 | 1·20 |
| {| 1/50 | 23·8 | 50 | 73·8| 173 | 382 | 555 | 2·21 |
| {| 1/40 | 11·7 | 50 | 61·7| 113 | 442 | 555 | 3·91 |
| {| 1/36·3 | 7 | 50 | 57 | 82 | 473 | 555 | 5·77 |
| | | | | | | | | |
| {| 0 | 139 | 50 | 189 | 504 | 280 | 784 | ·56 |
| {| 1/200 | 68 | 50 | 118 | 415 | 369 | 784 | ·89 |
| {| 1/100 | 35·7 | 50 | 85·7| 325 | 459 | 784 | 1·41 |
|60 {| 1/75 | 22·5 | 50 | 72·5| 265 | 519 | 784 | 1·96 |
| {| 1/52·3 | 7 | 50 | 57 | 160 | 624 | 784 | 3·90 |
+------+---------+-------+-------+------+-------+------+------+-----------+

Thus, on a level line, the engine, working up to 555 horse-power, could just draw 288 tons of train at the rate of 40 miles per hour, wasting on its own resistance only one-third of the power usefully employed on the train; but when the speed was increased to 60 miles per hour, it could not, though working up to 784 horse-power, draw more than 139 tons of train, wasting on its own resistance more than half the power usefully employed on the train. And again, at 40 miles per hour, though, as just stated, it could draw on the level 288 tons, it could only draw 24 tons of useful load at that speed up 1 in 50; while at 60 miles per hour, though it could draw, as stated, 139 tons of train on the level, it could only draw 23 tons of useful load up 1 in 75; and at the respective speeds of 40 and 60 miles per hour, it could only take one carriage (7 tons) up the respective gradients of 1 in 36, and 1 in 52.

Hence to maintain a minimum speed of 40 miles per hour with locomotive power on a line with long gradients of 1 in 40 involved on those parts of the line a wasted power of nearly 4 times that usefully employed; and if a minimum limit of 60 miles per hour were contemplated, a locomotive of the most powerful class in existence three years subsequent to Mr. Brunel’s report advising the adoption of the Atmospheric System would only have been able to take a single carriage up an incline of 1 in 52. So heavily at high speeds on steep gradients is the performance of a locomotive taxed by the resistance due to its own dead weight.[75]

* * * * *

A comparison has now to be made between the cost of power as developed by a locomotive and as developed by a stationary engine.

From the well-known experiments made for the information of the Gauge Commissioners in December 1845, taking the high speed trials as the basis of calculation, it appears that 4·5 lbs. of coke per horse-power per hour may be taken as the average consumption of the engine.[76]

It will be well, however, to allow for the improvement which was at the time anticipated in locomotive working, and to assume an expenditure of 4 lbs. of coke per indicated horse-power per hour, as representing the case then for the locomotive engine.

Coke may be taken to have at that time cost 21_s._ a ton, or ·0094_s._ per lb. Moreover, a careful analysis of the Great Western Railway half-yearly reports, for 1844 and 1845, shows that for every shilling expended in coke, 1·44 shillings were expended on the average in wages, oil and waste, repairs, etc.

Putting the results together, it appears that for each single indicated horse-power delivered by a high-speed locomotive, the cost per hour was 0·0915_s._ or 1·098_d._; that is to say, about 1-1/10_d._ per hour.

Let this now be compared with the cost per horse-power per hour at which the best Cornish pumping engines had long been known to perform the work. This comparison is manifestly a rational one--with reference to the kindred employment of engine power in atmospheric pumping-engines.

The performances of nearly all the pumping-engines in Cornwall were for many years so systematically and exactly reported, and the reports of each were so critically scrutinised by the rival makers, that the data they supply may be relied on without hesitation. It was well known that the best of the engines continuously performed useful work with a consumption of coal at the rate of 2·33 lbs. per delivered horse-power per hour, or, counting coal at 16_s._ per ton (a fair price on the South Devon), at the cost of ·2_d._, or one-fifth of a penny per horse-power per hour.

But it was not in its consumption of fuel alone that stationary power was the more economical; the expenditure in wages, oil, and tallow on one of the pumping-engines above referred to, when doing 200 horse-power of useful work, did not exceed 20_s._ for the twenty-four hours, or one-twentieth of a penny per horse-power per hour, while the cost of repairs was merely nominal.

Thus if fuel, wages, oil, and tallow be brought into one item, it is seen that the cost of one horse-power in stationary engines such as the then existing Cornish engines was only ·25_d._ per hour, or less than one-fourth of its cost when developed by a locomotive, which has been shown to have been 1·098_d._ per hour.

THE ROYAL ALBERT BRIDGE.

H. Adlard. Sc.]