On May 10, 7:44 pm, wrote:
I pull water from a lake and pump it up to my cottage. For some
reason, my pump has started short cycling. I changed the pressure
switch, and the pressure tank is fully charged (about 38 lbs). It is
primed. If I open the prime port and turn the pump in it shoots water
high into the air - getting water is not the problem.

When the pump comes on, it quickly builds pressure to 40 lbs and then
shuts off, pressure immediatley drops to 20, pump comes on, then off
very rapidly. Would a leak in the line between the jet pump and the
house cause this? I am thinking it might have frozen and split....

Others have covered all the points so I will just wrap it all up in
one:

1. Your pre-charge tank pressure is too high. Drain tank and re-
charge to 20 psi. If the problem stillpersists:

2. Leak? Quit possible, in the input line or a footvalve or check
valve. You can install a new checkvalve just prior to the tank. It
will work just fine.

I have assumed (I know, I know) that the pressure tank is in the
cottage. If it is co-located with the pump then the leak could be on
the house side and in that case you will have to find and fix it.

Harry K