Somethings you need to know before testing a solenoid valve

In this article, I want to talk about one important thing you should pay attention to before connecting a power supply to an unfamiliar solenoid valve for testing.

In many industrial devices and hydraulic systems, solenoid valves are critical control components. Although they may look like a simple coil, testing an unfamiliar DC solenoid valve incorrectly can easily damage the valve or create safety hazards. Some of you may have already guessed that I’m referring to polarized DC solenoid valves, meaning they have only one correct way to be connected to a DC power supply.

1. DC solenoid valves are polarized

Typically, these solenoid valves use asymmetrical connectors to prevent incorrect connections. However, in practice, if a proper plug is not available, people may substitute a few stripped wires, which can easily lead to valve damage or malfunction. Connecting the power supply incorrectly may also damage internal components or even cause a short circuit. Simply “plugging it in to test” is not always safe, especially for valve models you are not familiar with.

2. There may be an internal flyback diode

To protect the coil and the circuit, many DC solenoid valves have a small internal diode called a flyback diode. When the solenoid is turned off, the residual magnetic field in the coil can generate high-voltage spikes (inductive kickback), and the diode provides a path for this current, protecting the circuit from damage.

If you connect the power supply in reverse, the diode will be forward biased, effectively creating a short circuit. This can cause the current to rise instantly, putting extreme stress on the coil.

3. Possible consequences

The results of reversing the polarity can be much more serious than you might think:

• The diode may melt or burn out.

• The coil may overheat, be destroyed, or even produce smoke or fire.

• If the diode burns out, the valve may still operate, but it loses flyback protection, and future voltage spikes could damage the coil again.

Even with “low-voltage DC,” improper operation carries significant risks.

4. Testing recommendations

To safely test a DC solenoid valve, follow these guidelines:

• Always monitor current: During testing, observe whether the current is within the valve’s specified range. If the current is abnormally high, immediately disconnect the power.

• Use a current-limited DC power supply: Preferably one with adjustable current limits. This ensures that even if the polarity is accidentally reversed, the current stays within a safe range, preventing the diode or coil from being destroyed.

• Do not rely on experience alone to apply power: Even if the valve looks simple, never assume “just connecting it will work.” Always confirm the model, rated voltage, and polarity before testing.

Remember this:

Although DC solenoid valves may appear simple, they may contain polarity-sensitive protection circuits. Reversing the polarity can not only disable the valve but also create safety hazards. Before testing, verifying polarity, monitoring current, and using a safe power supply are essential operating practices for every technician.

Remember: nothing is more frustrating than a perfectly good solenoid valve being damaged due to improper testing. Safe and careful testing protects both the equipment and yourself.