For sanitary processing applications, valve diaphragm quality is greatly underestimated. It is not uncommon for biopharmaceutical companies to spend three months making a batch of drugs worth $30 million, only to have a faulty diaphragm threaten batch contamination and force the line to shut down while the damage is assessed and corrective action taken. Even so, many end-users continue to live with the hassle and cost of repeated diaphragm failures.
Many Original Equipment Manufacturers (OEMs) supply replacement diaphragms for their own valves, but problems can arise because most valve experts are not seal experts. All too frequently an excellent valve’s performance can be limited by a poor diaphragm. The reality is that diaphragm seals vary greatly and criticial material and performance data is frequently neither available nor well understood by the end-users who must shoulder the responsibility for their selection.
A Material World
The materials used to construct diaphragms are usually described by using a combination of brand names and classifications. Adding to the confusion is the fact that brand name materials can also have varying grades. Rick Schroder, Engineering Manager at Newman Sanitary Gasket, is all too aware of the misconceptions that are out there.
“Some end-users, when they specify a particular material, may only specify a generic material, like EPDM. They don’t realize that EPDM is a general class of polymers [ref. ASTM D5899] — EPDM varies widely in its performance and suitabililty for a given application. For hygienic applications, some are just better than others,” explains Schroder.
The “better” elastomers that Schroder describes are “created well and perform well. The way a material is formulated and processed in many ways determines its ultimate performance when molded into a static gasket or a dynamic seal like a diaphragm. The very same seal design can have vastly different performance simply because of the material selected and who fabricated it.”
Good materials often have a high polymer content, meaning that they have lower levels of clay, carbon black and other inexpensive filler materials. But polymer and carbon black content are only two of the criteria that Newman uses to gauge the quality and performance of elastomers:
• Extractables — Measures how much of the material can be extracted back into the process.
• Carbon black composition — FDA regulations require less than 50 percent for pharmaceutical applications and less than 10 percent for food and dairy applications (21CFR177.2600).
• Base polymer content.
• Sulfur content.
• Ash — Measures the inorganic material left over when you burn it.
Figure 1: Chemical testing on samples of EPDM from Newman and its competitors.
More detailed material tests also undertaken by Newman look at water and hexane extraction over varying time frames, the tensile strength, elongation, modulus, hardness, compression set and total organic carbon content of elastomers, in addition to the physical performance testing of finished articles.
Diaphragm Performance Testing
The cleaning process for sanitary systems can be particularly harsh on valve diaphragms. One of the performance tests used by Newman’s third-party testers involves exposing the diaphragm to 500 steam-in-place (SIP) cycles lasting one hour at 130°C. A higher quality diaphragm requires no retorquing during testing, and maintains the seal integrity, system pressure and its physical appearance after the 500 SIP cycles.
During the same test, the valve and diaphragm configuration is cycled (pulsed) 100,000 times. OEM diaphragms are typically guaranteed to less than 33,000 cycles, an indication of shorter working life.
Another set of diaphragm tests simulate air, water and SIP conditions under process pressures for a duration of one hour. Testers then look for any external leakage, pressure drop, torque loss and changes in appearance.
A big factor in the performance of diaphragms is the facing material used on the process contact side of the diaphragm in laminated and two-piece diaphragms. Just like elastomers, material selection and the processing of the facing material drives the ultimate performance of the seal.
Qualification & Traceability
With all of the equipment and materials within an hygienic area of a pharmaceutical plant controlled, it’s important to verify that any replacement diaphragm valves are “functionally equivalent.” This means that new parts with equivalent design and materials can be used as replacements for qualified parts. Otherwise, the expensive process of requalification may be necessary.
In addition, being able to trace all the details of the fabrication of a given diaphragm is important if a failure occurs. Newman has a patent pending on a molded-in marking system that uses a part number to trace the diaphragms origins.
In a perfect world, valve diaphragms are only replaced during routine preventative maintenance. The reality is that diaphragm failures will occur from time to time. These occurrences are an opportunity to review the diaphragms used in your system and look for replacements that can offer improved performance and longer life spans.