Poppet valve is a linear action valve in which the closure is a stem mounted disk often with an angled edge closing on an angled seat.
In one type of normally closed two-port solenoid controlled poppet valve shown in Figure 1, pressure at port A is applied to the back of the poppet via a small hole (orifice X) in the side-wall. Pressure keeps the poppet closed in the manner of a check valve. Energizing the solenoid lifts a plunger unblocking a hole (Y) in the center of the poppet. Imbalance occurs because of the pressure differential across orifice (X) and the poppet lifts permitting flow through the valve from A to B. Note that the solenoid armature (plunger) is permanently surrounded by the hydraulic fluid and hence balanced.