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• When towing portable two-wheeled ▪ compressors with a plated

30th October 1970
Page 45
Page 45, 30th October 1970 — • When towing portable two-wheeled ▪ compressors with a plated
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Which of the following most accurately describes the problem?

vehicle not kxceeding 3.5 tons gvvv, what is the permited maximum legal weight of the compressor lefore this weight must be added to the gvw if the towing vehicle to determine whether ir not an operator's licence is required?

Will such portable compressors have to pe fitted with stop lights to conform in lanuary 1971 with the new lighting requirenents, ref. Reg 32A 1969 C and U ?egulations?

• Compressors of the type you have des

' cribed are exempt from operators' censing, so there is no need to add the weight D that of the towing vehicle.

The stop-light requirements under the new egulations which are effective from January 1 971 do apply to such portable compressors Ind all other trailers, the term being used in its videst sense to include anything which is owed.

ri We are looking into the use of a small weighing machine to enable us to check wheel and axle weights before our lorries eave the factory.

Could you let us have your recommeniations?

& There are several companies manufacturing equipment of this type Ind of those we have seen and tested we would suggest that the following may be most ;Liftable for your application. A unit made by Neighwrite of Falcon House, Perimeter Road, Nood ley Aerodrome, Reading, Berkshire, omprises a pair of platforms, a track and .amp and a basic load indicator and costs 590. It is suitable for recording axle loads up :0 11 tons.

Another unit using hydraulics is the Davall irtovveigh and this is marketed by Kismet Ltd, yf Fenlake Road, Bedford. The cost of this init is approximately £350.

A third is the portable Checkweight weighing rnly 60Ib manufactured by Hawker Siddeley Dynamics Ltd, Devonshire Works. Dukes kvenue, London W4. The price of the Checkweight is £125.

ri1 change the diesel engine oil of my

fleet of heavy lorries strictly in accordnice with the maker's recommendation in wery case, which often necessitates dockrig a vehicle at an inconvenient time. A `ellow haulier in my area often defers :hanging oil until the vehicles have covered RS much as 50 per cent more than the -ecommended mileage without apparently ncreasing wear and tear of the power unit. rs such an extension permissible? And what are the factors that control the useful life of in oil between changes?

ABecause -the useful life of a lubricating oil depends on a number of variables, the change period recommended by an oil cornany or the vehicle maker is of necessity a compromise on the safe side, and it is Impossible to be specific regarding the permissible life of an oil in practice. The detergent additives of a modern diesel oil are "used up"

at a rate that mainly depends on the amount of soot produced by the combustion process and the amount of water vapour in the burnt gas that condenses into water droplets in the combustion chamber.

Free carbon, or soot, is the product of incomplete combustion, and apart from that which is discharged with the exhaust gas as black smoke the soot mixes with the oil and passes into the sump together with any condensate that may be present. Mixing soot, water and oil forms cold sludge.

A detergent is added to a lubricating oil to disperse the soot and/or sludge in a finely divided state in the oil and in this state the contaminants are virtually harmless. Water dispersed in the oil eventually evaporates, whereas sludge in the sump may be pumped into the oilways unless it is filtered out. Oilway blockage by sludge is a fairly common cause of bearing failure.

Moreover, if the soot is not dispersed in the oil a proportion will oxidize to form hard carbon deposits on the piston which tend to

"gum up" the rings and to increase the difficulty of efficiently lubricating the piston/ cylinder-wall surfaces. -Additive depletion" is

a continuing process, the rate of which depends on the work the additive has to do in dispersing the carbon and sludge. Given that the engine is in good condition, that it is not over-fuelled and that it does not operate at a sub-normal temperature for long periods, additive depletion is relatively slow and the life of the oil is extended compared with an oil that has to cope with heavy soot and sludge concentrations produced by overfuelling and frequent periods of cold running. While blow by is increased by wear of the pistons and cylinders and while this accelerates additive depletion it also increases oil consumption, and frequent topping up of the oil could make good the additive depletion to some extent. Although sludge is normally produced by cold running, it may be produced by operating over an extended period at or near the peak load. A high combustion temperature tends to oxidize the lubricating oil and if the oxide mixes with the unburnt oil it will form "hot sludge" that can be as harmful to engine operation as cold sludge. Lubricating oil may also be contaminated by dirt if the engine is operating in a dusty atmosphere without an efficient air cleaner and dust is a highly abrasive and penetrating material that can increase wear to many times the normal rate. Under ideal conditions an engine may therefore operate without undue wear if the oil change period is extended by two or three times the recommended period. But playing safe is obviously the best policy. Taking a chance could be very costly.

What is the basic design feature of the fifth-wheel coupling and how did it acquire this curious name?

I have always regarded the expression "cord" in application to tyres as relating to the early narrow high-pressure pneumatics. Is this correct and is there therefore any particular significance in the use of this

AA fifth-wheel coupling on a tractive unit of an articulated outfit is essentially a wheel in that it basically comprises a flat circular plate and there is angular movement between this plate and the mating plate of the semi-trailer when the tractive unit and semi-trailer articulate. lithe coupling is viewed as a wheel, it may be regarded as the fifthwheel of a four-wheel tractive unit. The description was undoubtedly derived from a colloquialism.

The basic design feature of a fifth-wheel coupling is the pin that links the tractive unit to the semi-trailer and allows angular movement between the two, without separation, in the same way that the sections of a folding rule can "articulate" relative to each other.

Obviously, a 'relatively large contact/rubbing area is required to accommodate the high pressure between the two plates when the semi-trailer is laden, in the interests of a long wearing life and stability. The pin is attached to the underside of the semi-trailer plate and is guided into its central position during the coupling-up operation by a V in the tractive unit plate. It is locked in position by a pair_ of jaws.

The description "cord" is now applied as a generic term that indicates the substance of which the carcass is made. Before the 1914-1918 war, square woven canvas was used in tyre construction. Later a cloth was developed all the strands of which were laid in one direction, and this cloth was defined as a rubberized cotton cord. Cord construction had considerable advantages over the original form with regard to strength and control of distortion.

That cords are employed in tyre construction is no longer of significance: it is the type of cord that is important and the manner in which the cords are arranged. As the name implies the cords of a radial tyre are arranged radially and combined with a braced tread this reduces deformation of the tread and "closing-up" of the ribs when the tyre is subjected to bump loads, which helps to maintain the drainage paths of the tread and to get rid of the water from the contact area when the vehicle is travelling on a wet road. And this improves the effective coefficient of friction of the tread.

Steel cords have the particular advantage that they increase the heat dissipation properties of the tyre and thus reduce an overheating tendency when a fully laden vehicle is travelling at a sustained high speed.


Locations: Reading

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