Views: 220 Author: shunhehandtruck Publish Time: 2025-03-05 Origin: Site
Content Menu
● Understanding Air Brake Systems
● Components of an Air Brake System
● The Trolley Hand Valve: Purpose and Function
● Proper Usage of the Trolley Hand Valve
● Avoiding Use During Normal Driving
● Integration with the Air Brake System
● Relationship with the Foot Brake
>> Citations:
The trolley hand valve, also known as the trailer hand valve or Johnson bar, is a crucial component in the air brake system of combination vehicles, particularly in tractor-trailers. This device allows drivers to independently control the trailer brakes, providing an additional layer of control and safety in various driving situations. In this comprehensive article, we will explore the intricacies of the trolley hand valve, its functions, proper usage, and its role in the overall air brake system of commercial vehicles.
Before delving into the specifics of the trolley hand valve, it's essential to have a basic understanding of air brake systems in commercial vehicles.
Air brake systems consist of several key components working together to ensure safe and efficient braking:
Compressor
Air tanks
Foot valve (treadle valve)
Brake chambers
Slack adjusters
Brake shoes or pads
In combination vehicles, additional components are added to control the trailer brakes, including the trolley hand valve.
Air brakes operate on the principle of using compressed air to apply force to the brake shoes or pads. When the driver presses the brake pedal, compressed air is sent from the air tanks through the brake lines to the brake chambers. The air pressure in the chambers pushes on a diaphragm, which in turn moves the push rod, activating the slack adjuster and ultimately applying the brakes.
The trolley hand valve serves a specific purpose in the air brake system of combination vehicles. Its primary function is to allow the driver to independently control the trailer brakes without applying the tractor brakes.
Typically located on the steering column or dashboard, the trolley hand valve is designed for easy access by the driver. It usually takes the form of a lever or knob that can be easily manipulated with one hand while keeping the other on the steering wheel.
When the driver activates the trolley hand valve, it sends a small volume of air at pressure to the trailer brake system. The amount of air pressure applied depends on how far the driver pushes or pulls the valve. This allows for precise control of the trailer brakes, from a gentle application to full braking force.
While the trolley hand valve provides additional control over the trailer brakes, it's crucial to understand its proper usage and limitations.
The primary intended use of the trolley hand valve is for testing the trailer brakes. Before starting a journey, drivers should use the hand valve to ensure that the trailer brakes are functioning correctly and responding to commands.
It's important to note that the trolley hand valve should not be used during normal driving conditions. Using the hand valve while in motion can increase the risk of trailer skidding or jackknifing, especially on slippery roads.
In certain emergency situations, experienced drivers may use the trolley hand valve to help stabilize the vehicle. However, this requires a high level of skill and should not be attempted by inexperienced drivers.
The trolley hand valve is integrated into the air brake system through a two-way check valve, which allows it to work in conjunction with the foot brake.
The two-way check valve ensures that the higher pressure from either the foot valve or the hand valve is directed to the trailer brakes. This means that if the driver is applying the foot brake and then uses the hand valve with greater pressure, the hand valve application will take precedence for the trailer brakes.
While the trolley hand valve controls only the trailer brakes, the foot brake applies pressure to all brakes in the vehicle combination. This difference in operation is why using the foot brake is generally safer and less likely to cause skidding or jackknifing.
Understanding the safety implications of the trolley hand valve is crucial for all commercial vehicle operators.
Improper use of the trolley hand valve can lead to several dangerous situations:
Trailer skidding
Jackknifing
Uneven brake wear
Reduced overall braking efficiency
It's critical never to use the trolley hand valve for parking. Air may leak out over time, potentially releasing the brakes. Always use the parking brakes and wheel chocks when parking a combination vehicle.
Regular maintenance and inspection of the trolley hand valve and the entire air brake system are essential for safe operation.
Drivers should perform daily checks on the air brake system, including the trolley hand valve, to ensure proper functionality. This includes checking for air leaks, proper pressure buildup, and correct valve operation.
Regular professional maintenance of the air brake system, including the trolley hand valve, is crucial. This should be part of the vehicle's overall maintenance schedule and performed by qualified technicians.
Proper training and certification are essential for drivers operating vehicles with air brakes and trolley hand valves.
In many jurisdictions, a Commercial Driver's License (CDL) with an air brake endorsement is required to operate vehicles with air brake systems. This training includes instruction on the proper use of the trolley hand valve.
Given the critical nature of air brake systems, ongoing education and refresher courses are recommended for all commercial drivers to stay updated on best practices and safety procedures.
As vehicle technology continues to advance, we may see changes in air brake systems and the role of the trolley hand valve.
Some newer vehicles are equipped with electronic brake systems that may alter or replace the traditional trolley hand valve. These systems often provide more precise control and integration with other vehicle safety systems.
As the industry moves towards autonomous commercial vehicles, the role of manual controls like the trolley hand valve may evolve or be replaced by automated systems.
The trolley hand valve is a vital component in the air brake systems of combination vehicles, providing drivers with additional control over trailer brakes. While its primary purpose is for testing brakes, understanding its proper use and limitations is crucial for safe operation. As with all aspects of commercial vehicle operation, proper training, regular maintenance, and adherence to safety guidelines are essential when dealing with trolley hand valves and air brake systems.
Q: Can the trolley hand valve be used to slow down the vehicle during normal driving?
A: No, the trolley hand valve should not be used during normal driving conditions as it can increase the risk of skidding or jackknifing. It's primarily for testing trailer brakes.
Q: How often should the trolley hand valve be inspected?
A: The trolley hand valve should be checked daily as part of the pre-trip inspection routine, and it should undergo professional inspection during regular vehicle maintenance.
Q: What should I do if the trolley hand valve doesn't seem to be working?
A: If you suspect an issue with the trolley hand valve, do not operate the vehicle. Have it inspected by a qualified technician immediately.
Q: Is it safe to use the trolley hand valve on slippery roads?
A: Using the trolley hand valve on slippery roads is especially dangerous and should be avoided. Always use the foot brake for normal braking in all road conditions.
Q: Can the trolley hand valve replace the need for regular brake maintenance?
A: No, the trolley hand valve is just one component of the air brake system. Regular maintenance of the entire brake system is essential for safe operation.
https://www.truckingtruth.com/cdl-training-program/page49/combination-vehicle-air-brakes
https://www.reddit.com/r/Truckers/comments/1hy9t43/how_does_a_trailer_air_brake_hand_valve_work/
https://www.gov.nl.ca/airbrakemanual/trailer-systems/hand-valve-and-two-way-check-valve/
https://sgi.sk.ca/air-brake/-/knowledge_base/air-brake/brake-application-hand-valve
https://www.edrivermanuals.com/georgia/commercial/combination-vehicle-air-brakes/
https://www.rvnetwork.com/topic/119902-trailer-brake-hand-valve-trolley-valve/
https://quizlet.com/818793236/combination-vehicles-4-cdl-flash-cards/
https://www.truckingtruth.com/truckers-forum/Topic-27952/Page-2/trailer-brake