SACA Pneumatics Practice Test

When a double solenoid valve uses two coils to move a single plunger, each coil is meant to pull the plunger in a specific direction. If both coils are energized at the same time, the plunger is being pulled in opposite directions or held between the two magnetic fields, so there’s little to no actual movement. The coil that is energized last ends up trying to draw the plunger into position while the other coil is already holding or resisting it. Since the plunger isn’t moving, that last coil ends up drawing current without productive mechanical work, which causes it to heat up and can lead to burning out the winding. This is the real risk of energizing both coils simultaneously. Other outcomes—like unpredictable movement, stalling, or a short circuit—aren’t the primary failure mode in this scenario. The main concern is wasted current and potential coil damage from the opposing magnetic forces. To prevent this, controls are designed to ensure one coil is energized at a time or to sequence coil energization to avoid both being on together.