Free Air Brake MCQ Questions and Answers

Question 1

How much force is applied to the push rod in a type 30 brake chamber when a 40 PSI brake application is made?

Accepted Answer

1200 PSI

Answer

The force applied by a brake chamber is calculated by multiplying the air pressure by the effective area of the diaphragm. A Type 30 brake chamber has an effective area of 30 square inches. Therefore, a 40 PSI brake application on a Type 30 chamber results in 40 PSI * 30 sq. inches = 1200 pounds of force on the push rod.

Question 2

When the air system reaches operational pressure, what does the compressor do?

Accepted Answer

Goes into an unloaded stage

Answer

When the air system reaches its maximum operational pressure (cut-out pressure), the air compressor governor signals the compressor to enter an 'unloaded' stage. In this stage, the compressor continues to run but stops pumping air into the reservoirs, instead diverting it back into the atmosphere or its intake. This prevents over-pressurization and reduces wear on the compressor.

Question 3

Between what two pressures should reservoir pressure be maintained?

Accepted Answer

80 (552 kPa) psi to 135 psi (930 kPa).

Answer

The air brake system's reservoir pressure should be maintained within a specific range to ensure proper braking function. The governor typically cuts in around 80 psi to start the compressor and cuts out around 135 psi to stop it. This range ensures there is always sufficient air pressure for multiple brake applications and safe operation.

Question 4

When conducting a build-up test on the compressor, what pressure do you start at?

Accepted Answer

50 psi (345 kPa).

Answer

When conducting a compressor build-up test, you typically start with the air pressure at 50 psi. From this point, you time how long it takes for the compressor to build the pressure up to the governor's cut-out pressure, usually around 125 psi. This test verifies the compressor's efficiency and proper operation.

Question 5

What is the lowest pressure at which the governor should trigger the compressor to resume its pumping phase?

Accepted Answer

80 psi (552 kPa).

Answer

The air compressor governor is designed to maintain air pressure within a safe operating range. It should trigger the compressor to 'cut in' and start pumping air when the reservoir pressure drops to approximately 80 psi. This ensures that there is always enough air pressure for safe braking and prevents the low-air warning from activating unnecessarily.

Air Brake Practice Test

Air Brake Practice Test

Free Air Brake MCQ Questions and Answers