In a direct acting valve, the solenoid core directly opens or closes the orifice, depending upon whether the solenoid is energized or de-energized. The valve will operate from zero psi to the rated maximum pressures. A pilot operated valve has a pilot and bleed orifice and utilizes line pressure for operation. When the solenoid is energized, the core opens the pilot orifice and relieves pressure from the top of the valve piston or diaphragm to the outlet side of the valve. This results in an unbalanced pressure, lifting the piston or diaphragm off the main orifice. When the solenoid is de-energized, the pilot orifice is closed and full line pressure is applied to the top of the piston or diaphragm, closing the valve.