PEAK (Apex) vessels

A vessel with a triangular base which occupies the zone of the vessel beneath the paddle is referred to APEX or PEAK (proprietary name) of the vessels. The vessels use exactly same set up as a traditional USP2 dissolution apparatus. The presence of the triangular base improves mixing within the vessel so there is less likely to be a mound of excipients/drug beneath the paddle.

From experience the mixing speed achieved in a USP vessel at 75 rpm is similar to that of a peak vessel at 50 rpm.
An example of a USP monograph dissolution method using PEAK vessels is the combination drug product Atovaquone/Proguanil HCl which uses a rotation speed of 50RPMs.