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Troubleshooting some common problems with AODD pumps
Despite being highly robust and reliable, installation and operation problems can occur with air-operated double diaphragm (AODD) pumps. We look at some of the most common problems and how to fix them within minutes.
1. Check the inlet air line size and pressure
A frequent mistake when installing an AODD pump is to use an air line that is too small. It will starve the pump of the compressed air it needs to operate at peak performance. Upgrading to a larger air line is an easy and quick fix.
You can find the appropriate air line size for the pump in the manufacturer’s installation and operation manual. As a general guideline, match the air line hose size to the air inlet port size on the air valve.
2. Inspect for muffler icing and restrictions
Diaphragm pumps can generate high decibels at full speed, which is why it’s recommended to install a muffler. The AODD air motor requires compressed air to operate. As the compressed air enters the air valve and channels through the pump center section to exhaust through the muffler, rapid temperature changes occur. At the muffler exhaust, air temperature is below freezing and can cause icing-related issues that are common in humid environments.
Erratic pump operation, inlet air with high levels of moisture or visible frost on the outside of the muffler are indications of an icing-related issue that can decrease pump efficiency. Some suggestions to avoid these issues are:
- Decrease the air pressure to the pump.
- Increase the pump size to operate at lower speeds (i.e. lower air pressure).
- Exhaust air to a remote location using an exhaust port tube.
- Add an air line filter with a water catcher and drain to collect condensation.
- Install an air line heater to raise the exhaust air temperature above freezing.
- Adjust the pressure dew point temperature with an air compressor dryer.
3. Inspect sealing surfaces for leakage
The first action upon discovering a leak is to ensure that the pump is torqued to the manufacturer’s recommended rating. Materials relax over time – often referred to as cold flowing – which can cause sealing surfaces to loosen and create leak paths.
Reuse of polytetrafluoroethylene (PTFE) O-rings is another cause of leakage at sealing surfaces. A downfall of PTFE is resilience. Once a PTFE O-ring has been compressed, it is not capable of regenerating its original shape. Replace all pump PTFE O-rings when servicing an AODD pump.
4. Ensure proper tubing and piping size
Pump inlet and outlet fluid port diameters vary based on the flow rate required. Inlet and outlet hose sizes must match the pump’s size. A primary concern is the risk of cavitation, which can increase repairs and maintenance costs. Changing tubing and piping size after installation is relatively fast. Knowing the correct size at installation eliminates the time and effort required to make a modification later.
For example, if a 1-inch pump has a half-inch inlet hose connected, the pump will not be able to operate at full capacity without the risk of cavitation. This risk increases dramatically as the desired fluid viscosity rises. In this example, the 1-inch pump should have a 1-inch inlet and outlet hose attached to prevent cavitation.
It is also recommended that an AODD pump be installed with a flexible inlet/outlet connection rather than being hard plumbed. As pump speed increases, vibration increases, which elevates the risk of loosening a hard plumb connection, creating the potential for leakage.
5. Slow the pump down to prime
AODD pumps are popular when self-priming is required. Creating a low-pressure zone – less than the atmospheric pressure of 14.7 psi (0.32 bar) – inside the fluid bowls is how the AODD pump draws fluid. If air pressure supplied to the pump is too high, the pump will change over too quickly and there will not be enough time for the fluid to be drawn into the pump.
To solve this priming issue in a matter of seconds, slow down the pump by using the air regulator to decrease the air pressure entering the air valve. Once the pump speed has been reduced and the fluid has had enough time to enter the pump, increase the air pressure and operate the pump at a faster speed.
6. Clear any fluid line restrictions
Certain restrictions create back-pressure that may negatively affect the pump and potentially create cavitation that will increase maintenance. Take a minute to inspect the pump and connected piping to ensure there are no visible restrictions. Look for the following at both the pump’s inlet and outlet:
- Closed or partially closed valves.
- Clogs or kinks in the line.
- Too much hose or length of distance.
Listen for erratic operation of the pump, which may be caused by an inlet hose that is too small or a problem related to icing. Hearing what sounds like gravel running through the pump or seeing flashing around the manifold elbows indicates cavitation and the need to correct the inlet or outlet tubing size or reduce the pump speed. Also, be sure to keep an eye out for kinks in the inlet and outlet lines or any valves that could be closed or restricted.
Any other problems?
Contact us and we will be happy to discuss any other problems you might be encountering with your AODD pump.
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