my family has a 350 gallon water tank bolted on a trailer which is used for a primary water source for a household water system. it is connected to a flotec model FP7120 pressure tank set at 28 psi which is connected to a Flotec Jet pump model FP4012 set at 30psi/50psi. now this particular setup doesn't have a check valve. when the pump is turned on, it constantly pumps. it never stops, it just keeps on pumping. I made sure that all of the faucets were turned off and there was no open conduit in the system so the pressure would be able to build to 50 psi. it does but 1 minute later, the pump starts again. My questions are, how important is it to have a check valve? does the pump itself act as an check valve? and if i need a check valve;where should it be installed; between the water tank and pump; or bewteen the pump and the house's water line?