Why Diaphragms Fail - SC Filtration

Why Diaphragms Fail

Many diaphragm pumps use two diaphragms, one for the fluid side and one right behind it. These diaphragms are sandwiched together to take advantage of chemical tolerances of each. For example, a Hytrel diaphragm is typically covered with a PTFE diaphragm because PTFE may be resistant to a chemical that Hytrel is not, or at least not as good compatibility as PTFE.

Of interest to note in this situation is that both diaphragms have different chemical compatibility, and they also have different elasticity.

The typical situation is where a user needs to create a vacuum to draw fluid into the pump. To do so, the impatient user revs up the pump to the maximum speed. Though diaphragm pumps can run dry, this stresses the diaphragms. Each stroke creates a stronger and stronger vacuum, eventually, the diaphragm swells like a balloon. When the pump cycles fast, heat is generated from the bending of the diaphragms themselves.

Critical failure happens when an extremely cold solution enters the pump. Let's say a -86F solvent hits a warm PTFE diaphragm running at 300 RPM. Instantly the PTFE reaches its Glass Transition Temperature and becomes brittle. It immediately shatters, looking like the picture on this post. Classic pump failure running crude. This is noted by the parallel fracture lines running from the diaphragm center to the outer edges.

Fortunately, this situation is avoidable. It's helpful to note that an AODD pump creates a stronger vacuum when fluid is running through the pump versus when it is empty. Running the pump dry is less efficient than running with fluid. To preserve the life of your diaphragm, run the pump dry as slow as practical, in the range of 25-40 PSI. A little patience will yield a longer diaphragm life and ultimately faster filtration rates. By slowing the pump and always keeping fluid in the pump, stronger suction is created and an optimal filtration rate is achieved.

If you must run your pump cold, we recommend removing the PTFE diaphragm if your pump includes one. Do so only if you are having frequent PTFE ruptures. Consider the above recommendations to prevent future failures and improve your filtration efficiency.


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