One of the most critical issues users of Air Operated Double Diaphragm Pumps (AODD) face is failure due to premature wear of the pump diaphragms. Below we will try to identify the main reasons that cause this problem and how it can be avoided:
Diaphragm Pumps Running dry.
When a pump runs dry, with no fluid in it, the pump will run faster than when it transfers fluid. Additionally, the consumption of compressed air increases dramatically, wasting energy.
We face two issues when a pump runs dry:
- Energy loss: a big volume of compressed air is wasted.
- Maintenance cost: an excessive pump speed means increased wear and diaphragms life reduction.
Running dry is probably the most common reason for premature wear failure in AODD (Double Diaphragm) pumps. It can easily be solved by:
- Using run-dry protection.
- Monitoring pump speed using external sensors.
We can identify when a pump has ran dry finding a circular tear of the diaphragm, Cavitation, which is produced when the pump suction is restricted, also produces premature wear with similar effects.
When priming a pump for the first time, we shall increase air pressure gradually while keeping the outlet valve open. The pump is primed once the fluid begins to flow uniformly/evenly through the outlet valve.
The air pressure exerts a force on each diaphragm that can create an excessive deformation., If the air pressure exceeds certain limit, it can permanently damage the diaphragm. In order to avoid these permanent damages, air pressure shall not exceed 8 bar – 115 psi.
To avoid excessive air pressure, specific regulators must be used. An air pressure regulator contributes to adapt pump speed to the application needs, controlling the air inlet pressure, and thus optimizing diaphragms life.
Pump’s Proper Torqueing
Specially in case of plastic pumps, it is highly recommended to fasten all bolts before using the pump for the first time, since fasteners may get loose during transportation. In order to do this, torque specifications, as mentioned in all manuals, must be observed.
- If diaphragms are over torqued: diaphragms may show cuts on the outside edge
- If diaphragms are under torqued: diaphragms may be pulled.
Pumping very abrasive fluids, like inks or slurries, produces abrasion of the pump. To reduce it ,the two following factors should be taken into account:
- Pump Size: the bigger, the better.
- Pump Speed: the slower, the better.
A good practice for pumping abrasive fluids, is to oversize the pump and to operate it slowly.
Impurities in the pump
Although AODD pumps can handle fluids with some solids in suspension, when pumping fluids with a large concentration of solids, the use of filters is highly recommended. Filters avoid impurities and particles from entering the pump and damaging the diaphragms.
In order to prevent any discolouration, cracking, bubbling or any other similar failure, the following temperature working ranges shall be observed depending on the pump materials:
|PTFE||5ºC – 105ºC / 41ºF – 221ºF|
|NBR||10ºC – 80ºC / 50ºF – 176ºF|
|ACETAL||10ºC – 90ºC / 50ºF – 194ºF|
|HYTREL®||10ºC – 90ºC / 50ºF – 194ºF|
|SANTOPRENE®||-29ºC – 135ºC / -20ºF – 275ºF|
|VITON®||-40ºC – 176,7ºC / -40ºF – 135ºF|
|POLYPROPYLENE®||10ºC – 80ºC / 50ºF – 176ºF|
|POLYVINYLIDENE FLUORIDE (PVDF)||-12,2ºC – 107,2ºC / 10ºF – 225ºF|
SAMOA Industrial offers only diaphragms manufactured with first grade and high-quality raw materials to guarantee longer diaphragm life. PTFE diaphragms are formed with three bonded layers, an air-side layer of EPDM, a central textile layer, and a fluid-side PTFE layer, to form a one-piece diaphragm that dramatically extends its working life. Bonded