As you already suspect, putting pumps in series is a bad idea if their respective output curves don't match reasonably well.
For the "pinching off", there are a few things involved. Ultimately what you are doing is converting pressure to velocity. How efficiently you do this is a function of geometry. A sharp edged orifice will have a higher head loss coefficient than a rounded-edge version. If your slots currently have 90° corners, you may see some minor improvement by rounding the inlet edges.
|