O-ring, 500x 3 mm – Viton, Part# 320535

This is a very large O-ring. Its part number is 320535. An O-ring is a simple loop of elastic material. Its shape is a perfect circle. When you look at a cross-section, it looks like the letter “O”. That is where the name comes from .

You place this O-ring into a groove between two large metal parts. When you tighten the parts together, the O-ring gets squished. It fills the tiny gap completely. This creates an airtight, leak-proof seal . At 500 mm across, this O-ring is about 20 inches in diameter. It is one of the largest seals in your DUO 255M pump.

This O-ring is made specifically for one pump model:

• Pfeiffer DUO 255M (Index C) 

The DUO 255M is a special version of the DUO 255. It uses a magnetic coupling instead of a traditional shaft seal . This design avoids oil leaks at the shaft. If you own this pump and are doing any internal repair or rebuild, you will need this O-ring.