1. Air Valve Stalling, Clogging or Leaking: Stalling of the air valve often has to do with the design of the airways inside the valve. If the design in less than optimal it will stall under certain conditions. Same can be said about leakage of air where the air mostly blows through the valve instead of being redirected to push the diaphragm. Clogging on the other hand could be due to the quality of the air you are using. Make sure you use filtered air to run the pump.
2. Diaphragm Rupture: The diaphragm in an AODD pump is always subject to mechanical stress and over time it causes stress cracks and failure. Material of the diaphragm combined with the method of manufacturing plays an important role in the longevity of diaphragms. Another important factor is the pressure. The higher the pressure the higher is the stress on the diaphragm. Lastly the number of strokes is the ultimate measure for the life of the diaphragm. Pumps that run faster will likely fail more quickly.
3. Check Valve Failure: Usually AODD pumps use ball style check valves. These check valves are likely to fail due to something getting in between the ball and the seat preventing a good firm leak-proof closing of the valve. Use of a strainer will reduce this possibility. Additionally flushing the pump when you suspect something is stuck often clears the check valves of debris. Wear of the ball and seat also causes leak paths. This wear could be due to abrasive particles in the liquid or just a matter of poor material choice for balls or seats.
4. Muffler Icing or Clogging: The main reason for the muffler icing is the content of moisture in air. Any moisture in the air condenses due to temperature drop when the air goes from high pressure to low pressure when it comes out to the atmosphere through a muffler. You may need to use dry air. Another reason of clogging could just be debris that gets collected over time. Use clean dry filtered air to ensure long trouble free operation of AODD pumps.
5. Torque Settings: Most AODD pumps are held together by bolts. Over time due to the consistent impact of strokes and liquid momentum the pump is subjected to some violent forces. This leads to the bolts getting loose. That in turn reduces the pressure on the sealing surfaces causing leakage. This is especially true for plastic pumps which are softer and the molded plastic surfaces tend to warp due to internal stresses. Re-tightening of the bolts periodically makes sure the sealing surfaces remain sealed. Also for softer plastics it is recommended to use reinforcement metallic plates.
Tapflo America AODD pumps had these and many more potential failure modes in mind when they designed pumps with machined plastic instead of molded plastic. They used reinforcement plates for softer materials such as PTFE. Their air valves are designed to be stall-proof. And their unique co-molded diaphragms last a very long time in the most challenging applications.