There are mainly 3 different technologies; direct acting, indirect acting and forced lifting piston types.
Direct-acting valves do not require a pressure difference to maintain their static state. In the NC type, once energized, they will only allow flow. These valves are very robust and can be used in production lines for safety purposes to achieve simple isolation purposes. It can also be used at the outlet of the fuel tank. Sometimes the pressure will become very low, but the valve needs to be kept open.
Indirect-acting valves require a pressure difference between the inlet and outlet to keep them at rest. For example, if the valve opens normally and the pressure difference is not large enough, the valve may be intermittent, and if the inlet pressure drops too low, it may close. These valves should only be used if the pressure level is within the parameters specified in the data sheet and IOM instructions.
Forced poppet valves are used in high-pressure applications, and neither type of valve can handle higher pressure processes, such as 40 Bar plus. The valve uses a larger and larger power coil to open or close, and the valve seat is directly connected to the bottom of the piston/plunger assembly, eliminating the need for a diaphragm.