OPINIONS FROM OTHERS.
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The Editor invites correspondence on all subjecis connected with the use of commercial motors. Leiters shouTd be on one side of the paper only and typewritten by preference. The right of abbreviation is reserved, and no responsibility for views
expressed is accepted,
The Inflation of Giant Pneumatic Tyres.
The Editor, THE COMMERCIAL MOTOR.
[2457] Sir,—Our attention has been drawn to an interesting and instructive article in the issue of The Commercial Motor for February 16th by Mr. L. G. Wyndham Shire on his experience of giant pneumatic tyres. We are glad to find that his views confirm ours with regard to the approaching rapid adoption of giant pneumatics on commercial vehicles.
As manufacturers for many years of high-class air compressors, we have very extensively studied the construction of small machines suitable for dealing with giant tyre inflation, and, after a prolonged series of experiments and tests, we have finally evolved a patent high-speed air compressor, which appears likely to meet the requirements to a very large extent. This type of compressor has recently been supplied to the Transport Department of the Egyptian Government, which has specified it to be fitted to its four-wheel-drive lorries, and we understand it is giving unqualified satisfaction.
We are aware that a number of small compressors has been fitted, as Mr. Shire states, to motor lorries without any conspicuous success, but we think the principal reason for their failure is that too much consideration has been given to the production of an article of low initial cost, rather than a highly efficient, reliable machine at a commensurate but moderate price.
Our latest garage type of small direct-motor-driven tyre inflator (shown in the enclosed illustration), which was recently demonstrated before an informal meeting of the Institution of Automobile Engineers, has given the following results when tested by a well-known tyre maker :— Pressure Size of Tyre. Inflated to. Time taken.
36 x 6 75th. 3 minutes.
34 x 7 85 lb. 4
34 x 7 100 lb. ... 5 12 40 x 8 103 lb. ... 64 „
The pressures given are those shown by the Schrader tyre gauge to be the pressure inside the tyre.
The above figures seem to indicate that the compressors we have evolved show considerable improvement over those which are mentioned in your article and which are said to "take very little less time than that taken by a good foot pump."
While there is a great deal to be said for the highpressure bottle at 1,800 lb. per sq. in., we might suggest that this system is hardly free from a certain amount of danger, owing to the very high pressure carried. One of the disadvantages connected with the bottle-charging system is that the power cost of charging a bottle to 1,800 lb. when the air is only required at, say, 95 lb. per sq. in. is considerable, and that a large proportion of this power is wasted, the only offset against which may be the advantage of convenience and portability.
All things considered, we are not at all sure that the final method adopted will not be the fitting of a thoroughly reliable, well-made, efficient air compressor on each vehicle, thus making it independent of any outside source for its air supply, although, no doubt, in many cases, like that of the Birmingham and Midland Motor Omnibus Co., some other system may be found more practical for the particular conditions prevailing. --Yours faithfully,
LACY-HULBERT AND CO., LTD., Pneumatic Engineers. C. E. LACY-HuLsEar, Managing Director. London, S.W.1.
The Editor, TEE COMMERCIAL MOTO%
[2458] Sir,--As manufacturers of small air coraPressors for the inflation of giant pneumatic tyres, we cannot allow to pass unchallenged the assertions made against machines of this type by the chief engineer of the Birmingham and Midland Motor Omnibus Co. in the issue of The Commercial Motor for February 16th.
In his opening remarks Mr. Wyndham Shire acknowledges his conversion from a sceptic to an enthusiast for pneumatics, but later indulges in adverse criticism on the cost of maintenance—a criticism which, he informs your readers, is supported by facts.
The section dealing with tyre inflation, however, is very far from a true statement of fact, and appears to be purely an expression of opinion, from which prejudice is not entirely absent. This is made only too evident when we see that claims are put forward in favour of one method which would apply much more forcibly to the method he condemns. This refers particularly to portability and safety—factors which are certainly more in evidence in mechanical pumps than in air bottles or cylinders, for which these virtues are claimed, It would be interesting to have the " facts" on which your correspondent bases the statement "that small compressors are hardly worth the initial cost and that the time taken to inflate an empty tyre is very little less than that taken with a good foot pump." This is likely to prove very misleading to a large circle of your readers, and we can only suppose that the condemnation of this type of machine is the outcome of inconclusive tests, probably made with inefficient air compressors costing, perhaps, very little more than the foot pumps with which they are compared.
A well-designed mechanical pump costing less than £10, and driven from the gearbox or any convenient point in the transmission system, will inflate a 40-in. by 8-in. tyre from flat to 95 lb. per sq. in. in 4i minutes, and will absorb approximately one brake-horse-power. The power exerted by a man continuously would probably not exceed one-eighth of this, so that we have a measure of the time likely to be taken with a foot pump. Four-and-a-half minutes and 35 minutes respectively are, in fact, fairly reliable figures, the accuracy of which we are prepared to demonstrate to anyone sufficiently interested.
The time is probably far distant when it will be possible to purchase high-pressure air cylinders at wayside garages in the same way that petrol is obtained at present ; but even if it were otherwise the cost of such cylinders at 5s. each, corresponding to is. per tyre, compares very unfavourably with a pump, whilst, in addition, therekis the inconvenience of transporting and fixing the heavy steel cylinders to the chassis to be considered.
For the user of fleets up to 25 or 30 vehicles it can be shown conclusively that small compressors fitted to each vehicle are by far the cheapest and best proposition, with regard both to initial outlay and cost of maintenance, whilst they also offer distinct advantages in the case of larger fleets. During the last 12 months this view has gained very wide acceptance amongst all classes of manufacturers and users of motor vehicles, and we feel sure that if your correspondence columns were opened to a discussion on this subject we should find a large measure of support for the small mechanically operated compressor.
In any case, in view of the widespread interest which Mr. Wyndham Shire's article is likely to attract, we trust you will give this letter prominence in your columns.—Yours faithfully,
Gloucester. WILLIAMS AND JAMES.
Makers' Experience for Motor Engineers.
The Editor, THE COMMERCIAL MOTOR.
[2459.1 Sir,—With reference to the letter No. 2449,
• over the signature of Mr. Rushton, of Birkenhead Corporation, in your issue of February 9th, upon the above subject, we entirely agree with him that it is desirable, in the best interests of both user and manufacturer, that the engineering staff of the user should visit the manufacturers' works to become thoroughly familiar with the best methods of maintenance.
With this in view, we always extend a hearty invitation to any of our new users to visit our works, but, unfortunately, the majority do not take advantage of the offer, which we consider is to be regretted.
With regard to obtaining the users' views, as manufacturers we have always paid the greatest attention to this point, and we have a system of free periodical Inspection, which we were the first commercial vehicle manufacturers to adopt, by which our inspectors visit the users, give them advice and assistance in the run
ning and maintenance of our vehicles, and at the same time obtaining the users' views. The information which we, from time to time; obtain is always given very careful consideration, and we have found it of the greatest possible assistance in perfecting our productions. Of course, it will be readily appreciated, with many thousands of users, that it is impossible to adopt all the ideas and suggestions that are put forward, but we do find that in the multitude of counsellors there is wisdom.—Yours faithfully, GUY MOTORS, Ian.
SYDNEY S. GUY, Managing Director.
Wolverhampton.
A Vulcan Performance.
The Editor, THE COMMERCIAL MOTOR.
[2460] Sir,—In the issue of The Commercial Motor for February 16th last On The advertisement pages) there is a testimonial about a 2-ton Vulcan terry. This Vulcan lorry has a mileage of over 25,000 to its credit, which took three years to cover, and it has done some very heavy work.
The owner states that the valves have never been ground in nor the cylinder head taken off for decarbonizing. T will not discredit this statement, but I shonld like to know if it is possible to get good results from an engine that has done as much running as this one, without grinding in the valves or cleaning the carbon deposit off the cylinder head. Surely the valves are worth grinding in and the carbon cleaned off the cylinder head once a year, when the yearly mileage is about 8,000?
From my experience of motors, I consider this a very good performance but bad economy, because the engine must have been robbed of its best pulling powers after the first 18 months of those three years through not having attention paid to the valves and carbon deposit.— Yours faithfully, H.E.D. Sheffield.