Question
QUESTION: I put in a new 1-1/4" PVC sand well point.  Installed a 1 HP pump, it pumps good (30 psi) with the garden hose wide open (no nozzle on hose).  Ran it this way for 1/2 hr, good steady pressure. When I throttle back the flow (with garden hose or using smaller sprinkler zones) the system gets air in it. Re-ran all the PVC line from well to pump. Still get air when flow is cut back. Must have a small leak in the PVC well casing above the well point.?  Can I repair this, sleeve it? Water level is 8 ft down. I figure air is getting in at higher flows also, but being pushed thru at a fast enough rate so not to build up in pump and start fluctuating the pressure. Pressure starts to jump 10 PSI when cavitation gets bad at the lower flows.

ANSWER: I agree, there is a leak somewhere, and it could be in the supply line or perhaps in the pump itself.  I don't know what your plumbing is, so can't comment on how to fix it outright, but checking every connection is the first line of order.

---------- FOLLOW-UP ----------

QUESTION: Thanks. I have narrowed it down to a leak in the 1-1/4" vertical line in the ground, from the top of the well to the water level. Can I repair it somehow? (with pumping something into a sleeve around it?) It's only 8 ft. to water.  Have already replaced all other PVC line from there to pump with new.  The check valve is right at the vertical line as it goes down to the well.  Check holds water from there to the pump.  I lose prime from my check valve down to the well when it sets over night.  

Answer
You can get a device called a repair band that fits over the pipe.  They are ususually metal with a rubber lining, and they bolt over the pipe.  An irrigation supply house (ones that sell to contractors) will most likely have them in the size you need.  Try places like John Deere Irrigation or Ewing Irrigation.  

This link should show a picture of different repair bands:
http://www.kukil.co.kr/eng/Html_eng/product2_2.htm