24v solenoid valve

Why is the connection between the 24v solenoid valve
A diode in parallel is just a light-emitting diode, which has no other effect than the role of luminescence. If the power of the power supply is reversed, it will not emit light and will not function as the indicator light. It doesn't affect the device.
A parallel diode is a continuation diode which ACTS as an antielectric potential of the discharge coil. When the coil is charged, the diode ends with a reverse voltage. If the power supply polarity is reversed, the power will be short and damaged. The polarity of the coil must not be reversed.