Dutch Bucket Help!

[wlai]

I'm having trouble with my dutch bucket setup. I have the below setup:

The pump has adequate head as it's 160GPH at 4.0 ft and this is less.

When I first start the pump the flow is good. However it'll start losing flow gradually after about 30 mins, and eventually dries up. Turning off and restarting the pump will restore the flow. I'm running the pump constantly.

I've tried various things, thinking it has to do with trapped air. For example, sometimes when I wiggle the pump when I can feel it vibrating but not pumping water, there will be some air bubbles come out of the body. I've also tried adjusting the high point of the 1/2" horizontal pipe, with out success.

As the summer starts going and I am not home to constantly restart the pump, I'm afraid I'm going to lose the tomatoes. Any clues and hints on what to diagnose and look for?

Thanks in advance,


William