I recently had to replace a mechanical plumbing vent, and the new one is smaller, is there different vents for certain uses? Did I put on the wrong valve? The drain doesn't go down like it would if there was no valve at all,I take the valve off and it goes down fast.Otherwise when the valve opens then it will go down, is this how it works?

What do you mean by "mechanical plumbing vent" ? Air Gap ?

Air Gap has standard dimensions. Inlet accepts 5/8" hose and outlet accepts 7/8" hose.