# Does a solenoid valve allow continuous run-time for very long durations?

I have a bunch of A4F010-06-BS-DC24V solenoid relays.

Can I use them on a continuous duty-cycle like certain relays or are they meant to be used only for certain duration at a time?

I'm worried about burning out the solenoid coils.

The original data sheet seems to be Japanese.

I have one more question which could be slightly off topic. I tried removing the solenoid connection part which were held by two screws. All I could see apart from the two screw holes was small 3 holes. I thought these solenoid valves actually had some "valves" that opened under magnetic field when activated. I was quite surprised when I noticed the inside with the solenoid to just have 3 holes and how does it control. When I tried connecting to a 24V DC I didn't see any visible movement apart from the click. Do you have any idea how it might be working?

The part with the red circle shows the tiny 2 or 3 holes I was talking about.

• I checked your coil, which power is low. Usually the coil life can reach over 5 million times. So you can use it at ease. The coil is not easy to be burnt or broken. Please note air valve needs to be far from water, please install a filter or FRL before the valve. It will be good for valve life. We have wrote an blog about coils, hope it is helpful for you. xpneumatic.com/how-much-do-you-know-the-solenoid-coil – Mac Chang Jan 24 '18 at 7:17

That looks like the same part as the CDK 4F0/1/2/3 series of solenoid valves.

There is no duty cycle limit on the coils listed in the datasheet. It would be very unusual for them not to be continuously rated. Note that they are solenoid - pilot operated rather than direct solenoid so they will be quite low power - 1.8 W according to the data sheet. You should be able to hold your hand on the coil when they've been powered for an hour.

Starting current and holding current

Note that the AC models have a higher starting current than holding current. This is because the inductance of the coil increases as the solenoid is pulled into the coil. Higher inductance means higher impedance and lower current. Since DC is not affected by inductance after the initial switch-on rise time the starting current and holding current are determined by the coil resistance only.

As a result of the above AC powered solenoids (and relays / contactors) have a built-in power saving advantage over DC. However, the very wide adoption of 24 V as the standard industrial control systems supply voltage means that we live with the power penalty.

DC solenoid power-reduction trick

Just because it came up in the comments ...

simulate this circuit – Schematic created using CircuitLab

Figure 1. A power-economiser circuit for a DC relay or solenoid. Full voltage is applied to the coil initially through its own normally closed (NC) contact but as it energises the direct connection is broken and the voltage-dropping resistor feed takes over.

Pilot operation

I have one more question which could be slightly off topic. I tried removing the solenoid connection part which were held by two screws. All I could see apart from the two screw holes was small 3 holes. I thought these solenoid valves actually had some "valves" that opened under magnetic field when activated. I was quite surprised when I noticed the inside with the solenoid to just have 3 holes and how does it control. When I tried connecting to a 24V DC I didn't see any visible movement apart from the click. Do you have any idea how it might be working?

Figure 2. 5/2 solenoid valve animation. Source: ZDSPB.com.

Explanation

Figure 3. Annotated for reference with text below.

This valve has five ports (1) to (5) and two positions (left and right). Hence, 5/2 valve.

• Pressure is applied at (1) and exits at (2) when the solenoid is off and (3) when on.
• (4) and (5) are the exhaust ports. Having two makes the spool (11) design very simple.
• (6) is the solenoid. This moves the actuator (7). Note that this is small and requires low power to move it compared with a direct acting solenoid which would move the spool (11) directly, and have to overcome seal resistance, etc.
• When the pilot is off mains air from (1) via (8) is fed into (10) to drive the spool to the right - the normal position. Output (3) will be energised while output (2) is vented at (5).
• When the solenoid is energised the pilot actuator (7) moves right to shut off the air to (10) and vent the left side of the spool (11) at (13) into exhaust (4). Mains pressure at (12) then moves the spool (11) to the left, port (2) is energised and port (3) is exhausted at (4).
• Note that while energised air pressure is applied to both ends of the spool but the surface area at (10) is greater than that at (12) so the spool moves right.

All that to answer your question: the split between main block and the pilot section in your valve may be a little different to the animation. Most likely the three holes are:

• The mains air supply to the pilot (8).
• The pilot itself, to push the spool (10).
• The pilot exhaust (13).

Note that there are many ingenious variations of these valves. Some might just use the spring at (12) and not have pilot air assist. In some the solenoid moves a tiny soft rubber diaphragm to allow air into (10).

Figure 4. The underside of the pilot valve.

(1) and (2) will be the pilot valve pressure supply and drive to the spool. How do we know? Because (3) has no seal gasket and the only place leaks don't matter is on the exhaust so (3) must be the exhaust port (13) on Figure 3.

• Thank you for highlighting and explaining the 24V part. It made me slightly confused if they meant the same relay can be run on both AC & DC. I've a starter solenoid with me, which I ocassionally used to run some heavy current applications. But they run pretty hot if we run for more than a minute. Thats why I thought I did ask before running the valve. – The_Vintage_Collector Nov 5 '17 at 15:57
• (1) A starter solenoid is designed for intermittent operation. (2) It is designed to pull in strongly and hold when the battery voltage collapses due to engine cranking. That means it will probably hold at about 3 - 4 volts. Since $P = \frac {V^2}{R}$ then running it at 12 V will result in 16 to 9 times more power dissipation than hold-in power. No wonder it runs hot! (3) Note that the coils only run on the rated supply. The 110 V AC version does not work on 24 V DC, etc. – Transistor Nov 5 '17 at 16:04
• Some DC solenoids assemblies have a low-resistance starting coil and a higher-resistance holding coil, and a switch that selects between them when they are retracted. Such assemblies can remain energized indefinitely without overheating if the switch disconnects the high-current coil, but may overheat in seconds if it fails to do so. – supercat Nov 5 '17 at 17:20
• @Transistor So, it means relays that draw higher current like starter solenoid around 7-8.5A drawn and have very powerful electromagnetic pull( I didn't mean the current capability of the NC/NO terminal) are meant for shorted duration. The ones with higher resistance coil are used for continuous duty cycle right? – The_Vintage_Collector Nov 5 '17 at 19:20
• I have a very good idea how it might be working. Read the update and see if you do too! – Transistor Nov 6 '17 at 8:38

It really depends on the model.

Some may have an activation current and holding current. The latter type would need to be initially activated with more energy to perform the "move" then held there with less force. That information will be in the spec sheet. I would however be surprised if this solenoid needed such handling. Things like this are usually controlled by simple mechanical switches and relays.

If you do not have a readable sheet but have the unit itself, you can test it with the full load and see if it gets hot.

BTW: A general issue with the holding current units is a power interruption can cause the thing to drop out and, even though the driver is still activated in low current mode, the unit will not return to the activate position. Depending on your application, that may or may not be an issue.

Most will be rated for continuous duty, some might be rated only for intermittent duty. It will tell you on the datasheet.

The limiting factor will be the temperature rise of the coils, not the valve body. You can easily estimate the coil temperature by measuring the resistance of coil when cold, and again later when hot. Copper has a tempco of about 0.4%/C, or 10% for a 25C rise. I would be happy running the coils up to a 50C rise, or a very measurable 20% in coil resistance.

Like relays, I would expect a solenoid valve to be able to hold in at below its pull-in current. If you find it does get too hot in continuous use, then you could experiment to see what lower current will hold it in, and run it just above that, rather than at 24v all the time.

Many solenoids will be able to withstand some level of current momentarily and a lower level of current continuously. Further, in most applications the amount of current that must be fed to an extended solenoid to draw it into position will be greater than the amount that must be fed into a retracted one to hold it.

Putting these two factors together, the way to get maximum performance out of a solenoid is typically to drive it with a high current initially, and then switch to a lower current (either by reducing the voltage, or cycling the voltage source on and off fast enough that the solenoid current doesn't go up and down too much).

Assemblies that use solenoids for some purpose (e.g. opening a valve) will typically only need a certain amount of force, and may use solenoids that can sustain the associated level of current indefinitely. If energy efficiency is a concern, it may be practical to drive such assemblies with a high initial current but reduce current once they're retracted. Assemblies where this is practical will often specify a holding current in addition to the activation current. One slight caveat is that some assemblies include a high-current activation coil and a lower-current holding coil, and automatically switch between them using a position-sensing contact. Such assemblies should generally be driven with a steady non-modulated voltage.

When driving solenoids, I typically will use "hit and hold" circuits. This is because most manufacturers will specify their coils to get smoking hot on their surfaces, i.e. near boiling / hot to the touch. Much of the medical equipment that I work on would be impacted negatively by this, and also are run off quality ACDC supplies that don't suffer from dropouts. Supercat and Trevor both made mention of this and it is a valid concern. However, if you're designing a PCB and are interested in dropping a circuit like this down, check the DRV103 from TI:

https://www.digikey.com/product-detail/en/texas-instruments/DRV103H/DRV103H-ND/390444

You can adjust the "hit" duration with a passive, the "hold" duty cycle with another passive, and you also get open circuit and overload indication via a fault pin. Not perfect for every implementation, but if you want feedback on the load from the PC level and reduced operating temp of the solenoid, this is a great way to get it.

• All fair technical points but industrial 24 V solenoid valves such as in the OP's post are generally directly operated from a PLC digital output and are simply on-off with the ability to run continuously on. What I have seen on one company's machines is the use of two-way stay-put double-acting solenoid valves. A coil is energised and when the actuator is detected in the desired position the coil can be de-energised as it can now be assumed the valve is in the correct position since the switch is on. This reduces the temperature of the coils. – Transistor Nov 6 '17 at 23:35