I see your point and initially that's what I thought, however, it turns out that the volume is not as important as the rate of flow which can interfere with the vacuum level achieved. I purposefully used 4" because the rate of flow is greatly reduced around the filter material allowing for inlet-outlet equilibrium. Without equilibrium the drop across the filter material will be manifest in total barrel vacuum. That's what the "cloth in the barrel vacuum port" caused and it's a 3/4 inch hole. Thanks for the comment, Evan
This seems like such overkill for the small volume of air that it's going to filter. I think you would do better with 2" schedule 80.
I see your point and initially that's what I thought, however, it turns out that the volume is not as important as the rate of flow which can interfere with the vacuum level achieved. I purposefully used 4" because the rate of flow is greatly reduced around the filter material allowing for inlet-outlet equilibrium. Without equilibrium the drop across the filter material will be manifest in total barrel vacuum. That's what the "cloth in the barrel vacuum port" caused and it's a 3/4 inch hole. Thanks for the comment, Evan