Pump/pressure tank detective needed

Hey guys,
My dad and I have a perplexing water problem that we can't reason out. Hoping there's some detective out there...
We have a shallow well and a jet pump, about 20m head to the house, a pressure tank and pressure switch in the house. System had been working great for 15+ years (same pump and tank too!), pressure switch is set from 30-45psi.
Here's the problem: Starting with a full pressure tank, we turn on some taps, water flows at a good pressure, the pressure gauge needle falls slowly as is expected. When the water pressure gets down to 30, the pressure switch makes an audible click but then instead of water rushing in and pressure going back up, the pressure falls fast to about 10psi and continues to trickle out the taps for hours. The pressure does not go up until we turn off all the taps. Once this is done, the pressure goes up fast again to 45psi and the cycle repeats.
??
The pump seems strong since it can pressure up fast to 45. The pressure switch (which we replaced brand new with no effect) is clicking at the right times.
Why would pressure fall fast at 30psi after the switch clicks? Why would the pump only start back up when all the taps are closed?
Any suggestions would very appreciated!! Thanks
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The pressure drops fast when the tank is close to empty. So, if the cut-in is set so that it occurs when the tank has almost no water left and the pump doesn't start instantly, you would see that.

That makes no sense, unless there is something more than an ordinary cut-in/out pressure switch on the system. Have you traced the wires, checked voltages with switch opened and after it clicks?

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On 5/4/2011 11:16 PM, Noland wrote:

Don't have a jet pump but have deep submersible. Had pump go a couple of times and when failing would overheat and not come back on until cooled. Last time, I was getting good pressure but if I used a lot of water, like in washing clothes, it would cut out. Plumber diagnosed by checking amperage used and it was double what it should be.
Also, have you been maintaining pressure in tank. If too low, it will cycle a lot which is not good for pump.
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