Should I Specify a Diaphragm Seal or an O-Ring Seal for my Control Valve?

I can tell you that most biopharm industry engineers will specify a diaphragm seal on WFI, and any media that comes in direct contact with final drug product.

For example, diaphragm seal control valves are used on WFI systems for end of loop back pressure control, on Buffer dilution skids and filtration skids for pressure and flow control and for Chromatography elution flow control.  Diaphragm seal control valves are also typically specified on Clean Steam applications.

O-ring stem seals, (what ASME BPE defines as sliding stem seals) are usually only specified for control valves on clean air and gas, and liquid clean utility applications like USP Purified water and some CIP fluids, but not all the time.

Here’s an example of a deviation from that norm – if particulate generation is a concern, a diaphragm seal control valve might be considered a better choice, as there is a higher probability of an O-ring shedding particles as the O-ring wears from contact with the stem.