Fire Hydrant System

I installed the system of fire hydrants in a building. Since last 3 days there is a loss of pressure in the system. The gauge indicates the pressure of 4 against 6 Paschal Paschal. And the motor starts running to increase pressure. When the pressure reaches 6 Pascal He goes back down to 4 Easter in 10 minutes and the engine is running again to increase the pressure. What could be the possible reason and solution for the problema

Edit *
Leaking pipe air is clear, an underground leak quite difficult, but depending on the volume of the leak, it may appear like a soggy field. The underground leak most likely be the last place of the modified piping - the new intake.
* Sometimes, a significant underground leak can be located by the sound, like a stethoscope.
A check valve leakage at the pump could be studied.
* A pump seal leak tree would be very obvious.

This is a problem of low flow or a leak or a restriction to flow other than the side of the pump.

sounds like a leak