Operation
The poppet valve is fundamentally different from slide and oscillating valves; instead of sliding or rocking over a seat to uncover a port, the poppet valve lifts from the seat with a movement perpendicular to the port. The main advantage of the poppet valve is that it has no movement on the seat, thus requiring no lubrication. The operating principle of poppet valves is described in the online article "How Poppet Valves Work". In most cases it is beneficial to have a "balanced poppet" in a direct-acting valve. Less force is needed to move the poppet because all forces on the poppet are nullified by equal and opposite forces. The solenoid coil has to counteract only the spring force.
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