The life of Isambard Kingdom Brunel, Civil Engineer

by Isambard Brunel

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.