loosing prime

I'm using a shalow well pump to pump from the river 100'. The pump pulls 11' high and has fair water pressure, however, I'm getting air from somewhere and loosing pressure. I'm using a sandtip point submerged in the river with a chack valve. I have one splice at 50' with four clamps. I tee'd of at the pump using the tee to fill the line and prime. Tefflon tape on all threads and double clamped at the 2" poly pipe barb. My question is, how do I trouble shoot the air problem? How can I tell if it's the connections or if it's coming from the pump? I don't really want to buy another pump if this one's good. Any suggestions??

It's pretty much trial and error. Or aggravation and more aggravation. You go to the joints, take them apart and re fit them one by one until you find the suction leak. check the check valve first though.

Make sure your check valve is also submerged under water, and remove any additional check valves in the system. Shaving cream on the joints will show a pin hole where air is being drawn in.

Many hours spent chasing suction leaks. Time that you never get back. The shaving cream thing works well. You can also pressureize the whole line and either listen for leaks, or soap the joints.

I have some sucesss with contact cement or 3m rubber adhesive brushed around suspect joints and allowed to dry.