Brake Application Pressure Tester
 Portable device for verifying application pressure during brake testing
Developed by:
Applied Vehicle Data, Inc., supplier of brake testing equipment
Verifies that brake application pressure during slack adjuster testing is 90 PSI or greater
Catches out-of-service trucks that pass at low brake application pressures
Sets up quickly and is portable
Verifies compliance with CFR and CVSA requirements
AVD Brake Application Pressure Tester
Summary of Features:
Verifies application pressure is 90 PSI or greater during slack adjuster testing
Light illuminates when brake application pressure is 90 PSI or greater
Portable design attaches to glad hands with light that lies on ground under vehicle
When performing slack adjuster measurement testing under vehicle, light can be seen from all brake chambers
Catching Out-of-Service Vehicles:
Vehicles tested at improperly low brake application pressure may appear to be “in service,” but when tested at the proper brake application pressure, these vehicles are out of service
Importance of Testing at Proper Application Pressure
Catching Out-of-Service Vehicles:
Vehicles tested at improperly low brake application pressure may have slack adjuster displacements that are less than 2 inches, but when tested at proper brake application pressure, these vehicles may have displacements that exceed 2 inches
Vehicles tested at low brake application pressure may appear to be “in service,” but when tested at the proper brake application pressure, these vehicles are out-of-service
Spring Brakes and Slack Adjustment:
Vehicles equipped with spring brakes with slack adjusters are approximately 98 percent of all off- and on-road trucks
Slack adjustment maintains clearance between the brake shoes and the brake drum
Slack adjuster clearance is critical because it is the primary factor in determining the ultimate braking capacity of the brake
Slack adjusters operate in a very narrow band of adjustment. For class 8 tractor trailers, normal adjustment of the slack adjuster is in the 1.5 to 1.75 inch range with the readjustment point at 2 inches
Example of Out-of-Service Vehicle:
Tractor-trailer was tested twice using a slack adjuster data acquisition system that captures the exact displacement of slack adjusters and brake application pressure
During first test, brake application pressure was 30 PSI and all slack adjuster displacements were 2 inches or less
During second brake test, application pressure was increased to 96 PSI
At 96 PSI all slack adjusters moved greater than 2 inches
Vehicle is out-of-service
The Items Included:
Self-contained pressure sensor that connects to glad hands
Indicator light that is placed on ground under vehicle
Connectors for power from vehicle
Calibration papers for pressure sensor
Custom-built fully padded cases for storage and transport
How to Set up the Brake Application Pressure Tester:
Connect pressure sensor to glad hands
Connect trailer cord to pressure sensor
Place indicator light under truck
While driver applies brakes, watch for indicator light to illuminate
Illuminated light indicates brake application pressure is 90 PSI or greater
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