Dual load-sensing standard on Guy tractors
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• All prime movers produced by Guy Motors are to be fitted with load-sensing equipment in both the service and secondary brake lines as an extra safety measure. Guy chassis use spring brake units to meet the main, secondary and parking requirements and the extra load-sensing unit will be incorporated immediately on the 32-ton Big J4, said to be currently the largest selling truck of this weight in the UK. It will be introduced on the other Guy tractors in the near future.
Dual load-sensing equipment was shown on a Guy chassis at the 1970 Commercial Motor Show and has been exhaustively tested. It has already been specified by some customers—notably the recent order for 214 Guy prime movers for National Freight Corporation and the orders for 35 units from Bulwark Contracts for British Steel.
The extra valve operates in reverse to the service line to counteract the effort of the spring brakes when the vehicle is unladen or partly laden and prevents sudden application of the driving axle brakes thus reducing the possibility of jack-knifing.
When the hand control valve is operated as an auxiliary brake the output pressure from the load-sensing valve is mechanically varied according to the height of the chassis frame in relation to the rear axle. Under light-load conditions the output pressure from the valve is almost equal to the input pressure and the high air pressure to the rear axle brake actuators serves to hold off the spring brakes partly and avoid over-braking of the rear axle. The lever and linkage is set before the truck leaves the factory to ensure correct operation.
Another detail change by Guy is that all trucks are to be fitted with a device enabling all flashing indicators to be actuated simultaneously if it is desirable to show other road users that the truck is in trouble. This device is already fitted to some cars in this country and is a widely accepted hazard warning on the Continent.