Design and function

Compressed air brake systems are typically used on heavy trucks and buses. The system consists of service brakes, parking brakes, a control pedal, and an air storage tank.

Supply system

The air compressor is driven by the engine either by crankshaft pulley via a belt or directly from the engine timing gears. It is lubricated and cooled by the engine lubrication and cooling systems. Compressed air is first routed through a cooling coil and into an air dryer, which removes moisture and oil impurities and also may include a pressure regulator, safety valve and a smaller purge reservoir.

Control system

The control system is further divided into two service brake circuits: the parking brake circuit and the  trailer brake circuit. This dual brake circuit is further split into front and rear wheel circuits which receive compressed air from their individual reservoirs for added safety in case of an air leak. The service brakes are applied by means of a brake pedal air valve which regulates both circuits. The parking brake is the air operated spring brake type where its applied by spring force in the spring brake cylinder and released by compressed air via hand control valve. The trailer brake consists of a direct two line system: the supply line (marked red) and the separate control or service line (marked blue).

Here are some things inspectors can do to improve there reports.

  • Ensure that all reports are factual and absent of personal opinion. Should the claim go to legal, the facts are all that matter, and an opinion may actually damage the case.
  • Verify all reports are definitive, and all questions that were asked have been answered.
  • If stating something appears to be pre-existing, document the proof to support it. (i.e. short or long term leaks, road grime build-up or the amount of play in a component).
  • Do not just state “per TSB” or the “technician said he had this code and this was the failure.” Request the technician demonstrate what was done to determine the failure, up to and including any specifications, electrical readings, codes, gauges or diagnostic trees.
  • Ensure photographs confirm the failure.  Multiple shots of front end components without the proof of excessive play are not beneficial. How was the failure verified? Perhaps the use of a dial indicator would be helpful.
  • Avoid discussing items with the technician or service advisor that are not on the repair order, yet discovered by the inspection. Instead, note it in the report, and the administrator will make the decision regarding the add-on.


Under Car Digest


Brakes, Exhaust, Chassis and More  

Click on photo to the right to see the online magazine.

Heavy equipment inspection overview click on link below



How a turbo works


Knuckleboom Crane
Knuckleboom Crane 

The knuckleboom crane appears similar to a standard crane, except that the boom articulates at the knuckle near the middle, letting it fold back like a finger. The key advantage of this type of crane is compact size for storage and maneuvering.

Knuckleboom crane arms are much lighter than boom truck cranes, and they are designed to allow for more payloads to be carried on the back of the truck that it is mounted on. The majority of them are mounted behind the cab and leave the entire bed of the truck empty. Smaller knuckleboom cranes can be used without a certified crane operator as long as the maximum capacity is under 15,000 pounds or the maximum boom length is under 25 feet.

The cranes come with different types of control systems, such as stand up, control from the ground, seat control, or radio remote control. The radio remote systems now can start the crane as well as run the crane. Now, they come equipped with a computer readout system that immediately gives readouts from the system if the crane is overloaded or not.

Water, Rest, Shade
How can heat illness be prevented?

Employers are responsible for providing workplaces that are safe from excessive heat. Employers should provide workers with water, rest and shade; should gradually increase workloads and allow more frequent breaks for new workers or workers who have been away for a week or more to build a tolerance for working in the heat (acclimatization); and should educate workers about the symptoms heat-related illnesses and their prevention. Employers should also include the steps to prevent heat illness in worksite training and plans as well as what to do in an emergency. Acting quickly can save lives!
OSHA's key pieces of advice for workers are:

  • Drink water every 15 minutes, even if you're not thirsty.
  • Rest in the shade to cool down.
  • Wear a hat and light-colored clothing.
  • Learn the signs of heat illness and what to do in an emergency.
  • Keep an eye on fellow workers.

Remember these three simple words: Water, Rest, Shade. Taking these precautions can mean the difference between life and death.

General Engine Diagnosis

For anybody interested this link can sharpen your engine repair, and rebuild skills and help with your ASE certification.                            


Driers and accumulators 

Are only good for a couple of years . 5 at max. The reason why is that one of there jobs is to remove moisture from the system because moisture is a non condense-able and moisture plus R-134A equals Hydrochloric acid, which is not good. After so long the internal desiccant bag becomes over saturated and can no longer do its job. 

The primary job of either two is the separation of vapor and liquid freon. The drier prevents vapor from passing into the liquid line and the accumulator prevents liquid freon from  passing through the vapor line. I know it sounds a little confusing but try to think of it like this.

If any vapor leaves the condenser and makes its way to the evaporator then you loose that much cooling efficiency because vapor cannot collect heat and if any liquid is allowed to leave the evaporator that has not converted to a vapor then it will travel straight to the compressor and " Slug " or damage the compressor since  liquid does not compress.