submersible well pump pressure loss only when outlets reduced

There are two faucets coming off the pump. If I reduce the flow of either one, water flow stops completely, waits about 15 seconds, then comes back on. If they're both wide open, it runs fine for an extended period.

It's a submersilbe pump to feed my barn, in a 75' dug well. No water tank or pressure tank; just a switch and a Square D pressure switch as protection. According to the previous owner it also has a pressure relief valve, but it's 4' underground, near the junction of the two faucet lines.

I tried bypassing the pressure switch, so now it's just the main power switch inline, but the problem persists. Is it possible that the pressure relief valve is faulty? Can the releif pressure setting have become lower somehow? Doesn't make sense.

The only other thing I can think of is thermal protection, but if that's the case why would the pump run wide open for extended periods without a problem? Thanks!

When the pump runs wide open there is a lot of cooling water passing by it. Decreasing the flow will make the pump run hotter.

This kind of a setup with no pressure tank ruins pumps in short order.

Decreasing the flow actually makes the motor run cooler, pulls less amps. That is unless the thrust bearing in the motor is bad. Then restricting the flow increases the amps and trips the overload. No pressure tank means the pump cycles rapidly. It is like shutting off a car engine while it is hot, the motor seizes up. You need a tank so you get enough run time to cool the motor before it shuts off, and also so it cools down before it starts up.

Look at it this way. If you have a pressure switch, you must have a tank. If you have a pressure switch without a tank, get rid of the switch and turn the pump on/off manually or with a timer. Just make sure there is flow while the pump is running. A pressure relief valve is just to keep excess pressure from breaking something. It has no way of shutting the pump off.