Q I am employed as a driver for a firm
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which operates mini-buses, these being 11and 13-seaters built to standard regulations and not p.s.v. specifications; most of our work consists of conveying staff to and from their homes for early and late duties.
Sometimes we are called upon to convey staff and passengers of subsidiary companies to their homes and stations, etc., and on such occasions as these a reciprocal journey is carried out by an associated company, thus the vehicles are plying for hire and reward. Could you tell me please whether, when the driver is engaged in the latter category he must be in possession of a p.s.v. drivers' licence?
AIf the vehicle is to be used for hire and
reward, the driver must hold a p.s.v. driver's licence. In addition, the vehicle—and this applies to mini-buses—must be built to meet the Construction and Use Regulations applying to public service vehicles and possess a current p.s.v. Certificate of Fitness. Furthermore, if the vehicle is used on a regular service on a Contract basis, the operator must obtain a licence for the service from the Traffic Commissioners.
Q/ believe the law regarding overrun brakes on trailers has recently been changed. What are the regulations concerning these?
AAs from January 1 1969 overrun brakes
are permitted only on load-carrying trailers with a gross weight of 31 tons or less. The regulations concerning plant trailers and caravans were amended on January 1 1968.
QThe vehicle I drive is not fitted with windscreen washers and I have been told that they are legally required. Could you tell me whether they should be fitted to my vehicle?
A Regulations concerning windscreen a" washers are contained in the Motor Vehicles (Construction and Use) (Amendment) (No 2) Regulations 1968 which came into force on April 8 1968. All vehicles first registered after October 1 1969 must be fitted with a windscreen washer capable of
clearing, in conjunction with the windscreen wipers, the area of windscreen swept by those wipers of mud or other similar deposit.
Existing vehicles, that is all vehicles first registered before October 1 1969, are exempt from this regulation until October 11972.
Exemptions to these requirements are land tractors and vehicles which are incapable by reason of their construction of exceeding 20 mph on the level under their own power.
/ have recently commenced in business
as a coach operator and I have heard that there is a register of coach operators within the United Kingdom who would be available for hire in the event of break down, or cases of emergency. Do you know of this particular register or any other publication which would be of assistance to me?
AAn inter-hiring list is published every two
years by the Passenger Vehicle Operators' Association Ltd., 12 Emerald Street. London, WC1. This contains addresses, telephone numbers, etc.
A similar list is available from AMI-Mutual Service (c/o PVOA at the above address) for Continental operators only.
am a student in a faculty of mechanical engineering in Yugoslavia and have read an article that refers to the "ram phenomenon" in induction systems of fourstroke engines. Could you exp fain the nature of this phenomenon and its importance in practice?
AIn any type of piston engme the flow of
air or fuel/air mixture into the cylinder is cut off temporarily by closure of the inlet valve or port. The diesel engine differs from a petrol engine in that the flow of gas On this case air) is not throttled to control output.
Consequently a surge is produced in the frovv of air which pulsates at a rate that varies in accordance with changes in engine speed and local pressure variations caused by bends in the manifold. At any speed and load condition, there are nodes or areas of higher and lower pressures in the manifold.
It is obviously desirable that a node of high pressure should be created in the area of the inlet valve when it is opening because this increases the amount of air entering the cylinder and therefore the volumetric efficiency. The "plug" of high-pressure air or mixture should also be as large as possible so that it may assist charging of the cylinder over a substantial part of the intake stroke.
When an engine operates at near constant speed and load it should be possible to -tune" the inlet manifold to give optimum filling by shaping the manifold to give a node of high pressure at the inlet valve. Unfortunately it is impossible to obtain a ram effect of this kind over a wide range of Speeds. but some makers claim that manifold tuning has produced a tarn effect over a "usefulrange. The problem of tuning a manifold is complicated in the case of a multi-cylinder engine because of the difference in lengths of the pipes or ducts between the inlet of the manifold and the inlet valves.
It may be of interest to cite the case of a single-cylinder motorcycle engine as a simple example of a unit that can be tuned to give a ram effect. in this case the length and diameter of the pipe between the carburetter and inlet valve are critical in that they can be varied to give a ram effect over a small range of speeds and outputs. Obviously, as indicated, the exercise is far more complicated if the manifold of a multi-cylinder engine is being tuned.
An exhaust system can also be tuned to improve performance over a narrow speed range by providing a node of low pressure in the area external to the exhaust valve, the exercise being complicated by the necessity to silence the exhaust gases.
Manifold and exhaust tuning patently has a limited potential if the vehicle is being used for general operations in which its speed and output are continually changing. If, however, the vehicle is regularly employed on motorways or the equivalent and covers long distances at near-constant speeds and engine outputs, the potential of tuning is much greater.
GI drive a 25 tons gross weight tanker which covers approximately 60,000 miles a year. What would be the advisable operational life of a vehicle of this kind?
A You do not say what make of vehicle it P.11 is and this is important because the operational life is governed by the quality of the vehicle as much as anything else. If your tanker is one of the cheaper makes the probable life at this yearly mileage would not exceed three to four years. With the mr.
expensive type of vehicle six to n would be more r •