hi guys just though i would tell you all how i solved my airlocking problem.
I have said about it on here a few times now as it was realy getting to me but at the start of every day i was air locked and sometimes through the day i just had very little pressure and had to keep takeing the hose from pump to di off to let the air out then it was good as gold.
tried a lot of advice from people but still had it on and off.
Then i was talking to my friend whos a plumber and he said get a ballvalve on the tank out let so when your water sloshes back to front of the tank there is no air pushed up the pipe to the pump.
Now went to a plumbers shop for £7 all done and problem solved and when i think about it it is obvious.
hope this helps someone else out
cheers joe