The air flow in truck brake system

02 Apr 2021

If engine is the heart of the truck, then air line will be acted as the vein. It runs through the whole truck body, included engine intake and exhaust system, high/low gear control of gearbox, servcie brake and parking system, engine exhaust brake system, axle diff. cylinder, air horn and cabin air suspension. Therefore, the best ways to protect your truck are keeping gas unobstructed and making every part of the truck play well together.

The air brake system is suitable for the dump truck, the tractor, the special vehicle and the engineering machinery. It is a necessary system for the heavy vehicle.

In the following picture, you can see the braking system of the truck, which has the most closed relationship with truck drivers.

Air brake system include service brake system and parking brake system, total 5 lines, we makr purple, blue, yellow, green and red color, will explain them as following:

I.Purple line and concerning parts: air fitler, air compressor, metal flexible pipe, air dryer assy, four circuit protect valve.

There are normale air paper filter, desert filter and oil bath filter for different truck, air filter was the vulnerable parts.

These are normal paper air fliter, suitable for tractor and clean work place.

This is desert air filter, can filter the big particle in the air, and keep truck going on well in a dust situation.

These are oil bath filter, the air was filtered by the oil pool in bottom of housing, suitable for tipper.

Being Cleaned through the air filter is going to be the first step even the most important step for the air to get into the truck body. The purity of the intake air determines the life expectancies of the air compressor and the engine. Thus, we recommend that you should use the original and regular product.

Air compressor makes low-pressure gas pressurized into higher pressure hot gas with the movement of the pistonand finally reach the air drier and four circuit protection valve through stainless-steel pipelines.

Vulnerable Parts and working principle:

Air dryer

The function of air dryer: clean the steam and release the redundant pressure.

2. Four circuit pretect valve

1 means air inlet

2 means air outlet, 21,22,23,24 means Number 1,2,3,4 outlet

Four circuit protect valve is the core parts for double brake system, it divided the air into 4 line, line 21 connect front brake system, line 22 connect middle/rear brake system, line 24 was for parking brake system. Line 23 was for other auxiliary air system. The 4 line was separeated.

3. Air compressor and the repair kit.

Air compressor suck low pressure air and outlet high pressure air. It was vulnerable parts.

II.Yellow line, front brake system, include four circuit protect valve, air tanker, brake master cylinder, front brake chamber.

Vulnerable Parts and working principle:

1 Brake master valve(Foot brake valve)

Brake master cylinder was air swtich, when brake pedal release, air inlet and outlet cut off, the air stop at inlet; when step on it, they were connect, air pass; when loose pedel, air inlet and outlet cut off, the redundant will be out though exhaust connector.

When air come into brake chamber, push the rod outside, the rod will move brake adjuster, brake camshaft, brake shoe, then make brake.

Air out, brake release.

IV.Blue line, act as service brake system, include four circuit protect valve, air tanker, brake master cylinder, service relay valve and middle/rear brake booster.

Series 1 means air inlet, 2 means outlet, 3 means exhaust, 4 means control.

When there is air in 4 connector, 1 and 2 will connect.

When no air in 4 connector, 1 and 2 will cut off.

IV. Green line, parking brake system, include four circuit valve, air tanker, hand brake valve, relay valve, middle and real axle brake booster.

Hand brake valve like an air switch, when it was at parking place, inlet and outlet cut off, exhaust open, no air in parking chamber, truck brake.

When it was released, inlet and outlet connect, exhaust close, parking chamber inflated, then release parking. 


When braking, step on the brake pedal, air can go to service brake chamber though relay valve. Puth the rod outside and move brake adjuster, brake camshaft, brake shoe, truck brake;

Release brake pedel, air out from service brake chamber, brake release.

When parking, hand brake valve was at park place, now the exhaust open, intake valve close, the air in the parking brake chamber out, the spring push rod outside, make parking.

Before truck move, pull hand brake vlave down, now the intake open, exhaust close, the air can arrive at brake parking chamber, inflate the spring, release brake

Above article is the base air brake system for rigid truck, there will be additional traier control valve, ABS valve on tractor and trailer, but we think, now you can handle some small problem after reading this, store some vulnerable parts in warehouse,  keep yout truck have an good attendance.