The function of jokey pump is to maintain the pressure in pipe line, pressure switch set at hi/lo to start the jokey pump motor, in case the pressure drop that jokey pump can't build up the pressure, then the main pump automatically start.
Jockey pump is working to keep fire hydrant system in pressurised condition always.If any pressure decreases in the system, automatically hydrant pump starts immediately to cope up the required pressure or supplying the required water to the required area.