When performing the maintenance on a pressurized Dry Chemical, Purple K, ABC extinguisher, it is the same as the other dry powder extinguishers. NFPA requires that certain steps, certifications, and equipment are used, while manufacturers might also require specific precautions, and steps as well. As long as an exterior visual inspection has been performed, the maintenance is as follows:

The first step is to dispense the powder, and nitrogen from the extinguisher. This is done by using a special type of closed recovery system, and stored within a sealed container. This ensures that the powder will not be contaminated with foreign objects, or debris that could cause a malfunction, or void the warranty/classification.
The second step is to take apart the assembly. This usually includes taking the hose and pull pin off. You then turn assembly head counter clock-wise. When performing this action, if there is any pressure left within the cylinder it could pose a danger to the technician, which is why it is done slowly to allow any remaining pressure to escape. When the spring, plunger, tube, and a rubber o-ring apart. The handle, top lever, and gauge do not come off, unless they are damaged and need to be replaced. The handle is attached with a special rivet, that fluctuates with each manufacturer, type, and size.
The third step is to use a small mirror, and light to inspect the interior of the cylinder. The interior of the cylinder could house corrosion, clumped up powder.

Each manufacturer has their own proprietary blend of dry powder, made of mostly the same ingredients, but mainly the ingredient Ammonium Dihydrogen Phosphate (ADP), also known as monoammonium phosphate (MAP).

The manufacturers require their own blend of the powder to be put into their extinguishers, to safeguard against the powder clumping, corrosion of the cylinder, and maintaining the warranty.. The liability, and warranty enforces the correct items, and powder is used for the correct extinguishers.

Manufacturers of ABC/Dry Chemical include

  
    Extinguishing Agent
    Method Of Operation
    Capacity
    Horizontal range of stream
    Approximate Time of Discharge
    UL or ULC Classifications
  

    Regular Dry Chemical 
(Sodium BiCarbonate)
    Stored Pressure
    1-2½lbs
    5-8 feet
    8-12 seconds
    2-10 B:C
  

    
    Cartridge or 
Stored Pressure
    2¾-5
    5-20 feet
    8-25 seconds
    5-20 B:C
  

    
    Cartridge or 
Stored Pressure
    6-30lbs
    5-20 feet
    10-25 seconds
    10-160 B:C
  

    
    Stored Pressure
    50lbs
 (wheeled)
    20 feet
    35 seconds
    160 B:C
  

    
    Nitrogen Cylinder or 
 Stored Pressure
    75-350lbs (Wheeled)
    15-45 feet
    20-105 seconds
    40-320 BC
  