How long have you been running the drippers like this? How much pressure does the pump generate?
I tried to do something similar but the pump filled a reservoir. That way the pump only had to run long enough to fill the reservoir. I had lots of problems with air in the line.
Right now i use an Oasis dripper meant for plants. It is a closed loop system so air is not a problem but it only has four preprogrammed timings. I ended up building a relay circuit to work around that but i would love to come up with something simpler while still reliable.