Answers to Queries.
Page 20
If you've noticed an error in this article please click here to report it so we can fix it.
Conditional Exemption.
[4180] (Driver in Kent).—If the certificate of exemption is based only on your being a steam-wagon driver, and does not make other service acondition, you needmot do the ambulance work.
Postage of "The Commercial Motor."
[4181] (Subscriber).—Many thanks for your action in drawing attention to the error at the foot of reply No. 4170. You are quite correct. The postage on this journal is id. A copy by post, therefore, costs 2d.
Pounds in Relation to Kilos.
[4182] (Shipping).—The following data should answer the points which you raise : 1 lb. equals .45359 of 1 kilogramme ; 1 ton equals 1,016.032 kilogrammes, which is 16.03 kilogrammes more than the metric ton of 1000 kilos. The metric ton is practically 2200 lb.
Buyer of an Agrimotor.
[4183] (City of London).—Nobody can get delivery of an agricultural motor at the present time except with the approval of the Department of Food Production, 72, Victoria Street, Westminster, S.W. A small type of British make, with self-contained plough, at a reasonable price, is the Wyles, made by Wyles Motor Ploughs, Ltd., of 5, Carr Street, Manchester.
Bridge Restrictions.
[4184] (Steam Wagon).—Section 6 'of the Locomotives 'Act of 1861 does not apply to heavy motorcars; exemption from the application of that section of the Act was conferred upon motor-wagon owners by Section 1 of the Motor Car Act of 1896. ,Restrictions on the use of bridges; in respect of weights beyond the ord:nary traffic of the district, can only be exercised where the party liable to repair the bridge complies with Article 14 of the Heavy Motor Car Order, as amended in 1907. On the other hand, any owner of a steam wagon who damages a private bridge may be held liable to make good to the owner of the bridge the, cost of such damage. No relief from this civil•liability, is conferred by any of the Motor Car Acts, as the liability is one at common law. Section 12 of the Locomotive Act of 1898 may be held to apply to heavy motorcars, in so far as extraordinary-traffic damage or damage to a bridge is concerned, notwithstanding registration of the vehicle under the terms of the Heavy Motor Car Order.
Electric Starting Sets.
[4185] (Van Owner).—We have not found it possible after taking all commercial factors into account, to give our general support to the suggestion that it is to the advantage of a rnotorvan owner to fit an electric self-starter, or to buy a van so equipped. A set of starting batteries may, for example, be exhausted in a very few minutes, if a careless driver continues to rotate the engine with unsuitable mixture coming from the carburetter. We have studied the instructions of not a few American makers of motorcars, concerning batteries for starting purposes, and they generally contain warnings of a most specific nature as to the riik of damaging the batteries by using them to start up the engine when it is cold, and above all until the engine has to a certain extent been " run in." In frosty weather, when an 'engine is generally harder than uszal to start, by reason of the thickening of the oil between the pistons and the cylinder walls, such damage to the starting batterieS is highly probable.
So far as saving of petrol goes, we consider that the rifik of extra outlay in Maintaining the ,starting batteries might very well exceed that economy, and that it frequently will do so in the hands of a commercialvehicle driver. Coal-gas for Goods Propulsion.
[4186] (Brewers)—Our issue of the 2nd Nevember last dealt as fully as was possible with the coal-gas situation. The difficulty is to get steel bottles, if you wish"to use gas under pressure. Any vehicle with a canopy can use a flexible gas-holder, and this can be replenished from an ordinary main, but the mileage for a 400 cubic ft. bag is not more than about 17 for a. four-tonner, and probably less in London. You will find that the issue of 2nd November also went into the matter of suitable compressors. Nobody has yet. worked out and tested a complete scheme of use. The. economy is absolutely certain, for 330 cubic ft. of gas is the equivalent, of one:fallen of petrol, and sometimes only 270 ft. are needed. We described and illustrated a well-proved valve, for regulation of the gas between pressure vessel and engine., last week., Ferro-concrete Bridges.
[4187] (Load).—We are acquainted with tests upon a highway bridge in ferro-concrete at High Wycombe,Bucks., which tests were conducted on the instructions of the Local Government Board by Messrs. David*Balfour and Son, of Newcastle-on-Tyne. This bridge was built in Mouchel-Heimebique ferro-concrete, under the' directions of the borough surveyor, Mr. F. J. Rush-brook. There is a single-arch span of 30 ft. between the' abutments, with a width of 36 ft. between the parapets. A 15-ton traction engihe, with a 10-ton. trailer behincl it, caused a deflection of only one-fifth of a millimetre at the centre of the span, and of onetenth of a millimetre at the sides. Messrs. Balfour, would, no doubt, furnish you with all the particulars. Such bridges undoubtedly provide a high factor of safety and a reserve of strength which are appropriate. to modern traffic.
Fabric Brake and Clutch Linings.
[41881Wesigner).—Experience does not bear out your contention. The best fabric brake and, clutch linings give better results than are obtainable with leather. The use of cotton brake-blocks was tried on horse-drawn tramcars some 20 years ago, .since which date great improvements have been effected in the manufacture of such friction fabrics. Mr. Herbert Frood, of Chapel-en-le-Frith, may be regarded as the pioneer of modern fabrics. He has improved both the bonding and the cernentitious elements. The co--efficient Of friction with cotton fabric, is about 0.7, or but little below that, and such a fabric can absorb more work in foot-pounds per sq. in. at a given pressure than can asbestos fabric. Conversely to leather, the co-efficient of friction with a cotton fabric rises with an ineeease of temperature. When the heat which is likely to be generated is-excessive, asbestos is practically obligatory. We believe the limit is nn the vicinity of 400 degrees Fahrenheit for cotton, or a little above that. The co-efficient of friction with asbestos is almost constant at 0.3.
In a recent paper, read at Glasgow before the Ass.o-, elation Of Mining Electrical Engineers, Mr. J. Oswald gave, the following as some of the general but preventableauses of failures with fabric lining :—(a) the use of wrong material; (b) failing to keep the fabric face clear of the opposing face when the brakes are out of action ; (c) failing to ensure that the fabric is kept well home when applied, or,-in other words, " followed up " ; (d) incorrect fixings of linings to the engaging media.; (e) expecting too much from brakes which have been under-dimensioned by the makers for the duties they have to perform. Either cotton or asbestos facings on clutches usually give smoother and more reliable transmission than leather, whilst as linings for brakes they give much better results than either metal or wood.