How many types of bubble caps are there?

• A. 6
• B. 4
• C. 5
• D. 7

Answer: (A)

Bubble caps on a tray are different cap geometries used to shape how gas bubbles through the liquid and how evenly the liquid is contacted. Over time, six main variations have become the standard categories in most training materials. Each type changes the way gas escapes the cap, how bubbles form, and how much gas bypass occurs, which in turn affects bubble size, distribution, and the overall pressure drop across the tray. That’s why six is the commonly cited count: it reflects the core set of cap designs engineers use to tailor performance for different operating conditions. If another source lists a different number, it’s just a different way of cataloging the same idea, but the six-type framework is the most widely taught.