Answer :
Final answer:
A greater air application to the trailer brakes when a tractor and trailer are coupled can be made using the trailer relay valve. This valve quickly applies pressure to the trailer brakes for safer braking. Hydraulic brakes use Pascal's principle to ensure even pressure distribution.
Explanation:
When a tractor and trailer are coupled together and a 30 PSI foot valve application is made, a greater air application to the trailer brakes can be made by use of the trailer relay valve. The hand valve is used for independent control of the trailer brakes, which can be essential during certain driving situations like correcting a trailer skid. The relay valve, which is part of the air brake system, ensures that the trailer brakes are applied more quickly and with the appropriate pressure needed for safe braking. This is in contrast to the safety valve, whose role is to prevent over-pressurization in the system, and the foot valve, which is the primary valve for applying brakes.
Hydraulic brake systems utilize Pascal's principle, where an applied force is transmitted through a fluid medium and results in the same pressure being applied at all points in the fluid. This can be seen in figures illustrating that a force applied to the brake pedal is amplified by the lever and hydraulic system, evenly distributing the pressure to the wheel cylinders. The identical slave cylinders or wheel cylinders receive equal pressure and consequently generate the same force output.
