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 resent 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 bad 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.
I.K.Brunel.
