Water Tank Pressure Problems? I have installed a 5000ltr dampen tank connected to a Bianco INOX60PC...

I have installed a 5000ltr dampen tank connected to a Bianco INOX60PC pump nom.pressure 150kpa.
This setup be installed to operate a Holman mains powered solenoid activate watering system, max pressure rated 1000kpa.

The outlet from the pump rises above the Water Tank but when I unfold the ball spigot on the water container the pressure of a full tank newly forces the water through the system, even when to some extent open.

What option are available to overcome this problem as we need to be assured the system is working effectively and the garde watered during our non-attendance.

The outlet
Please, I want answers! Answer if you know....
Answers:    Maybe the bladder in the container needs pressure adjustment. Check it and see.