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I need to control the following 2 ways direct solenoid valve ("Series 252 D01") :

https://www.emerson.com/documents/automation/catalog-series-252-dental-manifolds-asco-en-6779448.pdf

It is rated at 24 VDC. If I apply this voltage, the valves opens (it is normally closed) and it consumes approx. 170 mA (meaning its power is 4 W).

But the valve also opens up at approx. 15 V (it consumes 100 mA -> 1.5 W). Once it is opened, I can go down to 3 V (it consumes 0.18 mA -> 0.5 W), and closes at 2 V.

Because the solenoid heats up at 24 VDC (approx. 50 °C after 15 min), I was wondering if I could control it as follows : I open it at 24 VDC and maintain its opening by reducing the voltage to 3 V. I can achieve this behavior with a PWM and a transistor.

Do you think it is a good or a bad idea ? What could go wrong ? Is it something which is usually done or not at all ?

If not, is it possible to reduce the heat while maintaining the proper functionning of the valve ?

Thanks.

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  • \$\begingroup\$ It is always a bad idea to be below/higher or too near of limits specified by the seller on any equipment. So first try to specify how legit it can be from your needs. \$\endgroup\$
    – user201301
    Nov 16, 2021 at 13:39
  • \$\begingroup\$ Yes, "hit and hold" is relatively common with solenoid valves. Some valve datasheets do say not to do it, while others encourage it by specifying a minimum hold current. In any case be generous with margins. Current control is something to look at too. \$\endgroup\$
    – Pete W
    Nov 17, 2021 at 0:36

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You are seeing hysteresis on the operation of the valve and that is common with magnetic actuators.

Your approach is OK but be aware of a few points:

  • You might need to be confident that a random spare from the same supplier will work over the same operating range. You might find that a replacement was not as sensitive and either wouldn't pick up or wouldn't hold up.
  • Power dissipation will be \$ \frac {V^2} R \$ so reducing the voltage to 75% will result in a power reduction to 56%. There's no need to go as low as 3 V unless energy consumption is an issue.
  • I didn't check the datasheet but if it's a regular pilot-operated valve then the solenoid opens the pilot air which moves the spool under air-pressure rather than direct magnet operation. You might find that the valve behaves differently with variations in pressure if the solenoid is not able to open the pilot fully.
  • Related to the previous point, you might find that the valve switching response is different at lower voltage.
  • Be sure to put a snubber diode around the coil.
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  • \$\begingroup\$ Also note, if the unit experiences vibration or physical shock during operation, there will be less force available to maintain the current state (it could open or close.) Pressure/flow may further influence that behavior (when under-powered.) \$\endgroup\$
    – rdtsc
    Nov 16, 2021 at 14:01
  • \$\begingroup\$ OK, maybe I was too greedy with 3 V... If we take a look at the datasheet, it says that it can be controlled at -5% +10%. But -5% of 24 VDC is only 22.8 VDC which is not a great improvement... 75 % is 18 V. I don't know what to think of it : it will certainly work, but I am not within the specifications of the datasheet... :/ \$\endgroup\$ Nov 16, 2021 at 14:01

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