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NEWS | June 1, 2022

Stryker: Maintaining and Troubleshooting the Air Accessory Manifold

2nd Cavalry Regiment Battle Group Poland, Stryker armored vehicles sit in the motor pool in Orzysz, Poland
Photo by Charles Rosemond

Maintainers, ever wondered how the Stryker’s air accessory manifold functions? Or what’s the best way to identify and isolate manifold problems? This article answers those questions, so read on about this critical Stryker component.
Below are breakdowns not only of the air accessory manifold, but also its associated components, what each component does, common problems, root causes of malfunctions and service requirements, if any. These breakdowns will assist technicians troubleshooting and correcting issues.
Air Accessory Manifold

What it doesThe air accessory manifold houses eight (8) electrical solenoid valves that control the distribution of compressed air to the auxiliary air circuits on the Stryker.
These circuits include the engine brake, Hi-Lo transfer case shift cylinder, 4x8 and 8x8 differential shift cylinders, engage and disengage ramp shift lock cylinders and the periscope cleaner nozzle.
Each electrical solenoid valve has an override switch that bypasses the solenoid and allows the compressed air to reach its intended auxiliary air circuit.
The air accessory manifold also has a port dedicated for the air horn. It does not have an electrical solenoid that controls the horn because the compressed air is controlled by a manual lever that when pulled releases air to the horn.

Areas of concern include:
  • Pressure protection valve: Make sure the valve opens prior to reaching 75 psi and closes after reaching 75 psi.
  • W540 wire harness: Check for loose connections and damage from improperly stowed equipment. Be sure to properly disconnect and reconnect the harness.
W540 wire harness and PPV valve
W540 wire harness and PPV valve
  • Electrical solenoids
    • Use the bypass switch to isolate pneumatic versus electric malfunctions.
    • Check for leaks between the solenoid and manifold caused by a damaged O-ring. Ensure there’s proper routing of air lines to the air accessory manifold.
    • If tags on the air lines are missing, replace them. Check for fitting damage.​
Common malfunctions are:
  • Faulty electrical solenoid
  • Air lines to solenoids installed the wrong way
  • Loose or punctured air line
  • Loose cannon plug
  • Leaking air accessory manifold​
Root causes of malfunctions are:
  • Accidental damage caused by the driver’s gear or foot
  • Age of equipment
  • Incorrect installation
  • O-ring failure
Electrical solenoid valve and override bypass switch
Electrical solenoid valve and override bypass switch
Air Distribution Manifold

What it doesThe air distribution manifold supplies air to the air accessory manifold by way of the P6 inlet on the distribution manifold. Once the air begins to flow in at the P1 inlet of the air accessory manifold, it passes through a pressure protection valve that opens up when the air pressure reaches 75 psi. This valve is a two position, pilot-operated, spring-returned valve.
Air distribution manifold
Air distribution manifold

Once pilot pressure exceeds return spring pressure, the valve opens up and allows compressed air to reach the manifold. Once pilot pressure drops below return spring pressure, the valve closes and air flow no longer can reach the auxiliary air circuits. The manifold also has a safety relief valve that will blow off once the vehicle’s air pressure surpasses 150 psi.

Areas of concern are:
  • Safety relief valve 
  • Obstructed or loose air lines
  • Routing to and from the distribution manifold
  • Missing air line tags
Safety relief valve
Safety relief valve 
Common malfunctions are:
  •  Incorrect routing
  •  Loose air lines
Root cause of malfunctions:
  • Incorrect installation of the manifold
Air Dryer

What it doesIt contains two desiccant cartridges that filter and dry the compressed air entering the vehicle air system supply reservoir.

Note that the air dryer cartridge NSN has changed to NSN 4440-01-443-9031.
Air dryer
Air dryer
Areas of concern are:
  • Desiccant cartridges can get clogged and the desiccant can break down
  • O-ring failure; purge valve sticking or freezing
  • Fire caused by trash around purge heater
  • Desiccant cartridges clog the manifold and purge valve
  • Air dryer housing and cables can burn
  • Breakdown of filters
  •  Leaking air due to O-ring failure or not replacing O-rings
  •  Burned out heating element
Root causes of failures are:
  •  Lack of service
  •  Trash or debris
  •  Failure to replace cartridges
Required services include:
  •  Semi-annual replacement of the cartridge and O-ring
  •  Removing excess moisture in the air tanks
Note: Operators are now required to inspect the air dryer housing and cable connections for charring and black residue during PMCS. If any is found, report it to field-level maintenance for replacing because the vehicle is NMC. 
Air Tank

What it does: The air tank is a cylindrical container that stores compressed air for distribution to the vehicle air system. Prior to reservoir 1(wet tank) is a back pressure control valve in the supply line that includes a check valve to control air entering in the reservoir.  After entering reservoir 1, the air then moves to the distribution manifold.  From there compressed air enters the air accessory manifold for distribution to the auxiliary circuits.
Reservoir 1
Reservoir 1
Reservoir 2
Reservoir 2
Back pressure control valve
Back pressure control valve 
Areas of concern are:
  • Excess moisture in wet tank, reducing air volume
  • Leaking back pressure valve
  • Failure to drain air tanks
  • Excess moisture from unserviceable air dryers
  • Air compressor failure pushing contaminants (coolant or oil) in air system
Root causes of failures are:
  • Operator fails to drain the system like it says in the -10 TMs.
  • Not servicing air dryers
  • Compressor failure                       
  • Excessive moisture caused by an unserviceable air dryer purge valve
Services needed are:
  •  Drain tanks after each use
  •  Perform PMCS and report any air leaks to maintenance personnel
Accessory Circuits

What they doThe air accessory circuits are comprised of the engine brake, Hi-Lo transfer case shift cylinder, 4x8 and 8x8 differential shift cylinders, engage and disengage ramp shift lock cylinders, and the periscope cleaner nozzle. Also included on the air accessory manifold is a port dedicated for the air horn.

Areas of concern are:
  • Ramp lock shift cylinders
Ramp lock shift cylinders
Ramp lock shift cylinders
  • Differential shift cylinders
Differential shift cylinders
Differential shift cylinders
  • Engine exhaust brake retarder cylinder
Engine exhaust brake retarder cylinder
Engine exhaust brake retarder cylinder
  • Hi-Lo range shift cylinder
Hi-Lo range shift cylinder
Hi-Lo range shift cylinder
  • Periscope blower
  • Air horn
Common malfunctions are:
  • Seized mechanical components
    • Ramp paddle sticking
    • Lack of lubrication on ramp locks
    • Seized exhaust brake       
    • Seized differential cylinder
  • Leaking fittings
    • Faulty transfer case Hi/Lo cylinder often leaks air into the transfer case and can cause the air not to build up above 75 psi
  • Punctured air lines  Obstructed airline and/or nozzle
  •  Air lines installed backwards on the transfer case, causing the speed shown on the speedometer to read higher than the actual speed.
Root causes of malfunctions are:
  • Age of equipment
  • Lack of lubrication
  • Incorrect routing
  • Damage from improperly stowed equipment
Service required:
 Lubricate and engage the exhaust brake like it says in TM 9-2355-363-13&P (Sep 16), TM 9-2355-326-13&P (Sep 16) and TM 9-2355-311-13&P (Sep 16).
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