If PA#4 is always present wouldn't it be the elemination of PA#3 to make up three barrells of power. Release sequence 4,1,2 no load or unload of PA#3. What do you think Jeff? I like the question.
The Basic Patterns in the 6th Edition in Chapter 12 or both 3 barrell patterns . . . .
Drive Loading . . . Stroke Variation 1,2,3 and Pressure Point Combo is Double 1,3
Drag Loading . .. . Stroke Variation 2,3,4 and Pressure Point Combo Triple 2,3,4