Suction velocity of different vacuum heads

[APalmer80]

I've been trying calculate the capacity of one of our dust collection systems. It features four vacuum slots lined up (27 inches by 1 inch each) shown as #3 on the diagram attached.

Using a manometer, I took pressure measurements at points #1 and #2. Both were around 1.1 inwc, which translates to about 4250 ft/min. The pipe diameter at #1 is one foot, the pipe diameter at #2 is 8 inches.

I am trying to calculate the suction velocity at a distance x from the vacuum heads. I've been trying to wrap my head around finding this value. I know that my flow rate is: Q = A*V, and that the capacity Q1 in the #1 pipe should be the summation of the capacity of the four openings.

Is velocity going to change as you decrease the cross sectional area of the pipe? According to my measurements, it looks like velocity is staying constant in all ducts. Then the question becomes, is the air velocity at point #1 equal to the velocity at the opening at #3? Or are you increasing the air suction in ft/min as you decrease the area of the opening?

I appreciate any help in advance, thanks.

 

[APalmer80]

So to clarify, if I change the vacuum opening from a long rectangle slot of a single 1 inch circle, does the suction velocity increase, or does the flow decrease?