Q: Our company is getting low and unpredictable cycle life out of our diaphragm valves. This problem has caused us to implement standard operating procedures for frequent replacement of the diaphragms, which is costly and time consuming. What could be happening, and what are our options?
A: This is a common problem for diaphragm valves that are used in steam applications. In many nonsteam service applications, weir-style diaphragm valves may last as long as 40,000 cycles, but they fail quickly when placed in steam applications.
Diaphragm failure has two common causes: cycle life failure due to the diaphragm and valve design, and diaphragm failure due to steam cycling, whether from mechanical stresses or aging of the diaphragm in steam service. In a sanitary valve, the diaphragm acts as the body seal and the inlet-to-outlet seal; it plays a big role in how the valve functions. Diaphragms are typically either PTFE or elastomer. The standard PTFE design is a two-piece diaphragm with a PTFE diaphragm and a backup elastomer diaphragm to reduce cold flow. The elastomer is often best for cycle life, but the PTFE typically holds up better with the temperature requirements of steam sterilization. The pure elastomer design often provides higher cycle life, but cycle life may be significantly reduced under steam-sterilization conditions.
Look for a diaphragm valve that features a single-piece PTFE diaphragm designed for high temperatures and high cycle life. This design will give you the best of both worlds and help your company avoid costly change-out procedures. You may need to ask some pointed questions when you are specifying or purchasing valves, but that should help you avoid line shutdowns, system contaminations, and high maintenance costs in the long run.
—Mike Bridge, biopharmaceutical market manager at Swagelok
If you have a problem with your equipment or process, an industry expert may have the solution. Please send your question to Erik Greb, editor of Equipment and Processing Report, and we may be able to provide an answer in a future issue. All questions will remain anonymous.