Solenoid Valve Duty Cycle Explained: Continuous vs Intermittent Rating
One of the most overlooked specifications when choosing a solenoid valve is its duty cycle – how long the coil can safely stay energised. Pick a valve rated for occasional operation and then leave it powered all day, and the coil will overheat, the insulation will degrade and the valve will eventually fail. This guide explains what duty cycle means, how to read the rating, and how to specify a coil that will survive your application.
What "duty cycle" actually means
Duty cycle describes the proportion of time a coil is energised within a repeating cycle. It is usually expressed as a percentage, sometimes called the ED rating (from the German Einschaltdauer). A coil energised for 30 seconds and de-energised for 70 seconds within each 100-second cycle has a 30% duty cycle. A coil that stays powered indefinitely is 100% ED, also described as continuous duty or continuously rated.
The reason this matters is heat. Current flowing through the copper winding creates resistance heating, and the longer the coil is energised the more that heat accumulates. A short duty cycle gives the coil time to cool between operations; a continuous duty cycle does not, so the coil and its insulation system must be designed to run hot indefinitely without failing. For more on why coils warm up, see our guide on why solenoid valves get hot.
Continuous vs intermittent duty at a glance
| Characteristic | Continuous duty (100% ED) | Intermittent duty |
|---|---|---|
| Energised time | Indefinitely, hours or days | Short bursts with cooling gaps |
| Typical use | Normally closed valve held open all shift | Dosing, filling, pulsing, sequencing |
| Coil construction | Higher-class insulation, encapsulated | Standard insulation acceptable |
| Running temperature | Runs warm to hot – by design | Stays cooler between cycles |
| Risk if mis-specified | – | Overheating, insulation breakdown, burnout |
The key point: almost every general-purpose AC or DC solenoid coil on the market is rated for continuous duty, but you should never assume it. Always confirm the ED rating on the datasheet before committing to an application where the valve is held open for long periods.
How insulation class links to duty cycle
A continuously energised coil relies on its insulation class to survive its own heat. Insulation classes define the maximum permissible winding temperature, and common ratings include Class B (up to roughly 130°C), Class F (up to roughly 155°C) and Class H (up to roughly 180°C). A higher class means the coil tolerates a higher internal temperature before the insulation begins to break down.
Two coils of the same voltage can have very different real-world lifespans depending on their insulation class and how well they are encapsulated. For continuous duty in a warm environment, an F or H class encapsulated coil is a sensible choice. You can browse voltage and connection options in our solenoid coil selection guide.
Ambient temperature and the derating trap
Duty cycle ratings are quoted at a reference ambient temperature. Mount the same valve inside a hot enclosure, next to a steam line or in direct sun, and the coil starts from a higher baseline before it even adds its own resistance heat. The practical effect is that a coil comfortably rated for continuous duty in a 20°C workshop may run close to its insulation limit in a 50°C plant room.
When the ambient temperature is high, give yourself margin: choose a higher insulation class, ensure air can circulate around the coil, and avoid mounting the valve directly against hot pipework. The chemical compatibility guide covers media temperature limits too, which combine with ambient heat to define the overall thermal picture.
AC vs DC and inrush current
AC coils draw a high inrush current at the instant of switching, then settle to a lower holding current once the plunger has pulled in. If a valve fails to fully seat – because of debris, back pressure or an undersized coil – the AC coil can remain in its high inrush state and overheat rapidly, even within its stated duty cycle. DC coils draw a steady current with no inrush spike, which makes them more predictable for continuous duty and quieter in operation, though they can be slower to respond.
For applications that cycle very frequently or must stay open for long, uninterrupted periods, a DC coil with a suitable insulation class is often the more forgiving choice.
When to consider a latching valve instead
If your real requirement is to hold a valve open or closed for long periods while drawing as little power as possible, a latching (bistable) valve can be the smarter answer than a continuous-duty coil. A latching valve is switched between states by a brief pulse and then holds that position mechanically or magnetically with no ongoing power, so there is no continuous heating to worry about. This is ideal for battery-powered, solar or remote installations. You can compare configurations on our 2/2 to 5/3 way and latching valve page.
A quick specification checklist
Before you order, confirm: how long the valve will be energised in each cycle; whether the datasheet states 100% ED or continuous duty; the insulation class of the coil; the maximum ambient temperature at the mounting location; and whether a latching valve would remove the heating problem entirely. Getting these five points right at the specification stage prevents the most common cause of premature coil failure.
Not sure which rating you need?
Duty cycle sits alongside media, pressure, port size and connection type as part of a complete specification. For the wider decision, start with our guide on how to choose a solenoid valve, or use the Valve Search Wizard to narrow down suitable models. If your application involves continuous operation or high ambient temperatures, it is always worth a quick word with our team before ordering so we can confirm the coil is rated for the job.