Magom Brushless Pump

[Supermario]

From what your saying Rob " bursting hoses even when relief turned down " immediately tells me the relief is not in the correct part of system.
I don't know how the valve works, myself, I would resort to the old air pressure test. Disconnect the lines and verify that with each function the relief valve is also feeling the air flow.
Its like electrical terminology, the prv must be hooked in parallel not series.