I recently replaced a 1/2 horsepower shallow well pump with a 4 gallon pressure tank. The cut in is set at 30 psi and the cut out at 50 psi. The pressure tank is set at 28 psi. When I turn on the pump it runs and builds pressure to 50 psi and cuts out like it should. The system maintains the pressure until I put a demand on it, turning on a faucet. Once a faucet is turned on, say for using a sprinkler or garden house, the pressure drops down to the 30 psi and the pump turns on as it should, however, the pressure continues to drop down on the pressure gauge at the pump to 0 psi. The water continues to flow at the faucet but at a significantly reduced pressure. While the faucet is on and the pump is on the pressure never builds back up to the 50 psi. Once the faucet is shut of the pressure will immediately build back up to the 50 psi and shut off. Is my pump not able to keep up with the demand or is there something else that is keeping the pressure from building up while the pump is running and the faucet is on? Any help is greatly appreciated.