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BENDIX AD-SP SYSTEM PURGE AIR DRYER - User Manual

BENDIX AD-SP SYSTEM PURGE AIR DRYER
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1
®
SD-08-2415
Bendix
®
AD-SP
™
System Purge Air Dryer & SC-PR
™
Single Check Protection Valve
“SPIN OFF”
DESICCANT
CARTRIDGE
EXHAUST PORT
MOUNTING
HOLES (3)
AD-SP
™
air dryer aluminum body contains the following
serviceable components or assemblies; the turbocharger
cut-off valve, heater and thermostat assembly, delivery check
valve assembly and combined purge and relief valve
assembly. In addition, the non-serviceable purge control
valve is located in the body. All service and replacement
can be accomplished from the exterior of the dryer without
removal from the vehicle. The spin-on desiccant cartridge
is removed and installed using a “strap wrench.”
The AD-SP
™
air dryer has three female pipe thread air
connections identified as follows:
Air Connection Port ID Function/Connection
CON 4 ...................... Control Port (purge valve control
& turbo cut-off).
SUP 11 .................... Supply Port (air in).
DEL 2 ...................... Delivery Port (air out).
DESCRIPTION
The function of the AD-SP
™
System Purge Air Dryer is to
collect and remove air system contaminants in solid, liquid
and vapor form before they enter the brake system. It provides
clean, dry air to the components of the brake system which
increases the life of the system and reduces maintenance
costs. Daily manual draining of the reservoirs is eliminated.
The system purge designation is used because the
AD-SP
™
air dryer uses a small portion of system air pressure
from the supply and front axle service reservoirs to perform
the purge or regenerative function. An SC-PR
™
single check
protection valve or a valve that performs the same function
is always used in conjunction with the AD-SP
™
air dryer to
protect the service system.
The AD-SP
™
air dryer consists of two major component
groups, a spin off desiccant cartridge assembly and a die
cast aluminum body assembly. The desiccant cartridge is
self contained and serviced as a complete assembly. The
FIGURE 1 - AD-SP
™
SYSTEM PURGE AIR DRYER
DELIVERY PORT
EXHAUST PORT
SUPPLY
PORT
MOUNTING
HOLES (3)
TURBO
CUTOFF VALVE
HEATER &
THERMOSTAT
CONNECTOR
CONTROL
PORT

Table of Contents

Questions and Answers

  • D
    Damon BennettAug 14, 2025
    Why is my BENDIX AD-SP SYSTEM PURGE AIR DRYER Dehumidifier dryer constantly cycling or purging?
    • G
      griffinkarinaAug 14, 2025
      Your BENDIX Dehumidifier might be constantly cycling or purging due to excessive system leakage. If gauges show leakage, test for excessive service brake system leakage. For a single vehicle, allowable leakage is 1 psi/minute in either service reservoir. For a tractor-trailer, it's 3 psi/minute in either service reservoir. Repair and retest as needed. If leakage isn't shown on gauges, test for excessive supply system leakage by removing the drain cock or valve in the supply reservoir (wet tank) and installing an air gauge. Build system pressure, allow the air dryer to purge, and observe the air gauge in the supply reservoir. The pressure drop should not exceed 1 psi per minute. Perform tests 1 to 5 in the order presented.
  • R
    Robert CookAug 17, 2025
    What to do if air is escaping from BENDIX AD-SP SYSTEM PURGE AIR DRYER Dehumidifier air dryer exhaust during the charge cycle?
    • A
      alejandrocoxAug 17, 2025
      If air escapes from the BENDIX Dehumidifier air dryer exhaust during the charge cycle, it could be due to several reasons: * The air dryer purge valve may be leaking, in which case you should repair or replace it. * The compressor unloader mechanism might be malfunctioning; test it for proper operation and repair or replace the unloaders as necessary. * The governor could be malfunctioning, requiring testing and potential repair or replacement. * Air flow to the supply reservoir may be restricted, so check for kinked tubing or hose, un-drilled or restricted hose or tubing fittings, and repair or replace as necessary. Also, replace the desiccant cartridge. * Consider increasing the volume in the discharge line by adding length or size of line, or add a ping tank.
  • M
    Mark MccoyAug 20, 2025
    What to do if my BENDIX Dehumidifier is unable to build air system pressure?
    • J
      Jade WestAug 20, 2025
      If your BENDIX Dehumidifier is unable to build air system pressure, check the following: * Ensure the AD-SP™ air dryer purge control line is correctly connected to the governor UNL (unloader) port. * Inspect the purge control line for kinks, plugs, or damage. Check for undrilled or restricted hose or tubing fittings. Repair or replace as necessary. * Test the governor operation and repair or replace as necessary. * Test the compressor unloader mechanism and repair or replace as necessary. * Check the operation of the AD-SP™ air dryer heater and thermostat. Repair or replace as necessary if the AD-SP™ air dryer purge valve piston is frozen open. * If the AD-SP™ air dryer purge valve piston is stuck, check operation and repair or replace as necessary.
  • J
    Jennifer HamiltonAug 25, 2025
    What to do if air is escaping from BENDIX AD-SP SYSTEM PURGE AIR DRYER Dehumidifier air dryer exhaust port during entire purge cycle?
    • B
      Bryan JordanAug 25, 2025
      If air is escaping from the BENDIX Dehumidifier air dryer exhaust port during the entire purge cycle (compressor not running), the following could be the cause: * A leaking turbo cutoff valve in the AD-SP™ air dryer. Verify the purge cycle has ended by noting the dash gauges. Perform Air Dryer “Operation & Leakage Tests” and repair or replace as necessary. * A leaking purge piston o-ring in the AD-SP™ air dryer. Perform Air Dryer “Operation & Leakage Tests” and repair or replace as necessary. * A leaking or malfunctioning purge control mechanism. Replace the AD-SP™ air dryer. * A leaking delivery check valve. Perform Air Dryer “Operation & Leakage Tests” and repair or replace as necessary.
  • R
    Robert HernandezAug 30, 2025
    Why is desiccant material being expelled from the BENDIX AD-SP SYSTEM PURGE AIR DRYER Dehumidifier purge valve exhaust?
    • S
      sototheresaAug 30, 2025
      Desiccant material being expelled from the BENDIX Dehumidifier purge valve exhaust, or unsatisfactory desiccant life, can be attributed to several factors: * Ensure the air dryer is securely mounted to minimize vibration by adding bracket supports or changing the air dryer mounting location if necessary. * A defective desiccant cartridge may be the cause; replace it. * The compressor may be passing excessive oil. Check for proper compressor installation; if symptoms persist, replace the compressor.
  • K
    kbauerSep 2, 2025
    Why BENDIX Dehumidifier is unable to build air system pressure and air is not escaping from AD-SP™ air dryer exhaust?
    • B
      brittany43Sep 3, 2025
      If your BENDIX Dehumidifier is unable to build air system pressure and air is not escaping from the AD-SP™ air dryer exhaust, consider the following possibilities: * A frozen discharge line. Inspect the discharge line installation for water traps that could freeze. Refer to the “Connecting The Air Lines” section in the manual and repair or replace as necessary. * A malfunctioning compressor unloader mechanism. Test the compressor unloader mechanism for proper operation and repair or replace as necessary. * A malfunctioning governor. Test the governor for proper operation and repair or replace as necessary. * Restricted or plugged airflow to the service brake system.
  • D
    Deborah RobertsSep 6, 2025
    Why does my BENDIX AD-SP SYSTEM PURGE AIR DRYER make excessive “pinging” noise during compressor loaded cycle?
    • S
      Shelly FlowersSep 6, 2025
      A slight “pinging” sound may be heard during system build up when a single cylinder compressor is used in your BENDIX Dehumidifier. If this sound is objectionable, it can be reduced substantially by increasing the discharge line volume. This can be accomplished by adding an additional four feet of discharge line or adding a 90 cubic inch reservoir between the compressor and the AD-SP™ air dryer.
  • B
    Brittany SchroederSep 9, 2025
    Why does the BENDIX AD-SP SYSTEM PURGE AIR DRYER air dryer purge piston cycles rapidly in the compressor unloaded mode?
    • J
      jillmcdowellSep 9, 2025
      If the BENDIX Dehumidifier air dryer purge piston cycles rapidly in the compressor unloaded mode, it may be due to the compressor failing to “unload.” This can be caused by faulty governor installation where there is no air line from the governor to the compressor, or the line is “kinked” or restricted. Install or repair the air line.
  • B
    bstricklandNov 26, 2025
    What to do if BENDIX Dehumidifier air dryer does not purge or exhaust air?
    • B
      Brian TorresNov 26, 2025
      If your BENDIX Dehumidifier air dryer does not purge or exhaust air, consider these potential causes: * Air might not be reaching the AD-SP™ air dryer purge control port. Test to determine if air flows through the purge control line to the purge control port on the AD-SP™ air dryer when the compressor is unloaded. Check for undrilled fittings and inspect the purge control line for breaks, disconnections, misconnections, freezing, or damage. Repair or replace as necessary and replace the desiccant cartridge. * The AD-SP™ air dryer purge valve or piston may be frozen closed. Check the operation of the AD-SP™ air dryer heater and thermostat. Repair or replace as necessary and replace the desiccant cartridge. * The vehicle may have extremely high air usage requirements. Refer to the Veh...

Summary

Description

Operation

General Operation

Explains the two operational modes, Charge Cycle and Purge Cycle, of the air dryer system.

Charge Cycle

Details the process of compressed air entering the dryer and becoming cleaner during the charge cycle.

SC-PR Valve Description

SC-PR Valve Operation

Charging

Explains how air flows through the SC-PR™ valve during the initial system pressure build-up.

Preventive Maintenance

Operation and Leakage Tests

Installing the SC-PR Valve

Repairing the AD-SP Air Dryer

AD-SP Air Dryer Removal

Steps for safely removing the AD-SP™ air dryer from the vehicle.

Disassembly for Part Replacement and Kit Installation

Guides on disassembling the dryer for component replacement and kit installation.

Retrofitting the AD-SP Air Dryer

Vehicle Application Requirements

Vehicle Preparation

Essential steps to prepare the vehicle before installing the air dryer system.

Mounting the AD-SP Air Dryer

Installing the SC-PR Valve

Specific instructions for installing the SC-PR™ valve during air dryer mounting.

Connecting the Air Lines

Wiring the Heater and Thermostat

Testing the AD-SP Air Dryer

Procedures for testing the electrical components of the air dryer system.

AD-SP Air Dryer Troubleshooting Chart

Appendix A: Maintenance Schedule and Usage Guidelines

Appendix B: Additional Troubleshooting Information

BENDIX AD-SP SYSTEM PURGE AIR DRYER Specifications

General IconGeneral
CategoryDehumidifier
TypeAir Dryer
BrandBendix
ModelAD-SP
Maximum Operating Pressure150 psi
ApplicationAir Brake System
Dew Point-40°F (-40°C)
MountingFrame

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