Depending on the type of material being handled, especially the amount of abrasives and solids, ePTFE could be the best diaphragm material.
by Michael Brooks
November 21, 2017
softened diaphragmImage 7. The fluoroelastomer diaphragm was softened by the temperature and exposure to a cleaning solution. Various abrasives in the media caused it to rupture.

Abrasives in the media drastically reduced the diaphragm life. Initially, the company used two-piece PTFE diaphragms with rubber backings, which developed concentrated areas of wear that cracked and flaked off into the process media and pump motors. The PTFE was forced into the air side of the pumps, which damaged their air distribution sections and cost the company more than $5,000 per pump in downtime, repairs and other costs.

The company’s maintenance, repair and operations (MRO) distributor suggested using an ePTFE composite diaphragm with molded-in ribs to reduce concentrated flex points and compare its performance to the diaphragms they had been using.

After five weeks of operation, the two types of diaphragms were removed from the pumps and examined (see Images 8-9).

diaphragm after five weeksImage 8. The original conventional PTFE diaphragm after five weeks of pumping hydrochloric and sulfuric acids, metal shavings and particulates

The ePTFE composite diaphragm showed no crease marks or signs of significant wear or chemical attack. The two-piece diaphragm was torn apart by the metal flakes, and the elastomer backing had indications of wear and chemical attack, eventually leading to rupture and pieces of the diaphragm mixing with the media. Because the composite diaphragm is bonded together, the ePTFE does not disintegrate easily and enter the media.

The ePTFE composite diaphragms lasted more than seven months, while the original two-piece conventional PTFE and elastomeric diaphragms lasted an average of five weeks.

3. Mining Company

A precious metals mining company wanted to get better life out of the diaphragms in its vertical AOD pumps. These pumps operated outdoors at temperatures ranging from 15 to 100 F and inlet pressure of 40 pounds per square inch (psi) for more than 20 hours a week. The media typically consisted of 70 percent hydrofluoric acid concentration.

ePTFE after five weeksImage 9. The ePTFE composite diaphragm after five weeks of operation

The company used chlorosulfonated polyethylene synthetic rubber until it was discontinued by the primary manufacturer before trying fluoroelastomer and EPDM as replacements. These diaphragms had to be replaced every four weeks. Each replacement required two employees working an average of seven hours. This added up to 22.75 work days annually per pump.

The company’s head of maintenance selected an ePTFE composite diaphragm. It was tested for six months and the company retrofitted its pumps with ePTFE composite diaphragms. Now on a routine maintenance schedule where the diaphragms are replaced every six months, the company is experiencing greater efficiency resulting from decreased wear on their pumps and systems, less downtime and reduced maintenance. Employees are also less likely to be exposed to highly corrosive acids while repairing the pumps.

4. Automobile Manufacturer

A major U.S. car manufacturer was using primarily AODD pumps to move phosphoric, sulfuric and hydrochloric acids and an abrasive slurry of dirt and metal flakes. The temperature of the media ranged from 100 to 120 F.

The company was using AODD pumps ranging from one-half to 3 inches with varied diaphragm life. They were using two-piece conventional skived PTFE and elastomer diaphragms with an average life of three months. Eventually, however, the company selected ePTFE composite diaphragms as a more durable alternative.

Testing began and the difference was noticed within months. The PTFE was no longer fragmenting and breaking off into the media; wear from the metal flakes was greatly reduced; and the rubber was not being attacked by the phosphoric acid. Based on these test results, the company began changing out the failed diaphragms for ePTFE composite diaphragms, extending diaphragm life from three months to 18 to 24 months and reducing downtime by more than 80 percent.