BS 4639:1987 pdf free download.Specification for Brakes and braking systems for towed agricultural vehicles.
1 Scope
BS 4639 specifies requirements for the brakes and braking systems of towed agricultural vehicles in combination with agricultural towing vehicles (normally agricultural tractors).
It contains braking requirements for the towed vehicle and for the towing vehicle to ensure their compatibility and requirements for the characteristics and performance of the complete braking system.
Conditions of test are given in Appendix A and tests for service brakes and parking brakes are given in Appendix B and Appendix C respectively. A specimen test report is given in Appendix D.
NOTE The titles of the publications referred to in this standard are listed on the inside back cover.
2 Definitions
For the purposes of BS 4639 the following definitions apply.
towed agricultural vehicle
an agricultural trailer, the main purpose of which is to carry agricultural produce, or any towed agricultural vehicle having a maximum weight exceeding twice its unladen weight but not being an agricultural trailed appliance conveyor
2.2
agricultural trailed appliance conveyor a trailer having an unladen mass not exceeding 510 kg which is designed and constructed for the conveyance of not more than one agricultural trailed appliance and which has each of its wheels fitted with a pneumatic tyre
2.3
agricultural trailed appliance
a trailed implement or machine constructed or adapted for use off roads for agricultural, horticultural, or forestry purposes and having a maximum weight not exceeding twice its unladen weight
2.4
balanced vehicle
a towed agricultural vehicle generally having two or more axles so that the weight of the vehicle is supported by its road wheels when the vehicle is detached from the towing vehicle
2.5
unbalanced vehicle
a towed agricultural vehicle, so constructed that part of the weight of the vehicle is not supported by the road wheels when the vehicle is detached from the towing vehicle, e.g. having one axle, or two axles if closely spaced
2.6
brake control
that part of the braking system which is directly actuated by the driver
2.7
inertia (over-run) brake
a service brake actuated by a compressive force in the hitch between towed and towing vehicles
2.8
service brake
that brake normally applied by the driver to decelerate a moving vehicle
2.9
unladen weight
the weight of the unladen vehicle
2.10
maximum weight
those maximum axle and gross weights stated by the manufacturer to be technically permissible
NOTE These weights may be greater than the “maximum weights” authorized by the national administration.
2.11
maximum mass
the mass corresponding to the maximum weight
2.12
unladen vehicle
a vehicle in running order with, where appropriate, its tanks and radiators full and carrying only a driver of mass 75 kg, but no optional accessories or load, where these are applicable
2.13
independent braking
the braking of the towing and towed vehicles by separate independent controls operated by the driver in the driving position of the towing vehicle
2.14
simultaneous braking
the braking of the towing vehicle and the towed vehicle by a single control operated by the driver in the driving position of the towing vehicle and where the muscular energy of the driver is not the energy used for braking the towed vehicle
2.15 Axle
2.15.1
two stub axles which are fitted on opposite sides of the longitudinal axis of the vehicle
2.15.2
any axle other than a single stub axle, whatever type or number are fitted to the vehicle
3 Braking requirements for towed
agricultural vehicles
3.1 Service brakes
3.1.1 Towed agricultural vehicles shall be fitted with the following types of braking systems, according to their maximum masses.
Not exceeding 0.75 t: no brakes required:
0.75 t to 3 t: any type of braking
system;
3 t to 8 t: over-run, independent or
simultaneous braking;
More than 8 t: simultaneous braking.
Where an over-run device is the only means of operating the brakes the maximum mass of the vehicle shall not exceed 3 500 kg.
3.1.2 Every towed agricultural vehicle which is required to be fitted with a service brake shall have braking devices which act on at least half of the vehicle’s wheels. These braking devices shall act on all the wheels of at least one axle and the action of these brakes shall be symmetrically distributed between the wheels in relation to the median longitudinal plane. An effective means of adjustment shall be fitted so that the brakes can be easily adjusted and be compensated for any wear.
3.1.3 The service brake of a towed agricultural vehicle shall be capable of achieving a braking force equal to at least 25 % of the maximum weight of the vehicle.
3.1.4 Braking systems on towed agricultural vehicles employing fluid transmissions shall be capable of accommodating a maximum nominal pressure of 150 bar’ for hydraulic systems and 8 bar for pneumatic systems.
3.1.5 Braking systems on towed agricultural vehicles employing fluid transmissions shall not operate when the pressure is less than 5 bar in hydraulic systems, or 0.5 bar in pneumatic systems.
3.2 Parking brakes. All towed agricultural vehicles required to have a service brake shall be fitted with a parking brake complying with 5.2.
5.1.4 Hydraulic braking systems shall be tolerant of high quality solvent refined paraffin mineral oils containing balanced additions, and any other transmission oils which are regularly used for the machinery of agricultural engineering.
5.1.5 In the case of simultaneous braking, with a fluid pressure at the coupling of 100 bar for hydraulic systems or 6.5 bar for pneumatic systems, a braking force equal to at least 25 % of the maximum weight of the vehicle shall be achieved, when tested in accordance with Appendix B. on both towing and towed vehicles, with pedal or hand lever forces not exceeding 600 N or 400 N respectively.
NOTE The preferred maximum pedal or hand lever forces are 450 N or 250 N respectively.
5.1.6 In the case of independent braking, with a fluid pressure at the coupling of 100 bar for hydraulic systems or 6.5 bar for pneumatic systems, a braking force equal to at least 25 % of the maximum weight of the vehicle shall be achieved, when tested in accordance with Appendix B, on the towed vehicle, with pedal or hand lever forces not exceeding 600 N or 400 N respectively.
NOTE The preferred maximum pedal or hand lever forces are 450 N or 250 N respectively.
5.1.7 In the case of an over-run brake a braking force on the towed vehicle equal to at least 25 % of the maximum weight to be borne by its wheels shall be achieved, when tested in accordance with Appendix B. with an input force of not more than 6 % of the maximum weight to be borne by its wheels.
The brakes shall not operate when the input force is less than 2 % of the maximum weight to be borne by its wheels.