I have a small volume, like few ml, at pressure of 100Kpa, which I have to reduce to 700kPa at a variable rate, say 10-50 seconds. I was thinking of using a 5V mini solenoid valve which I plan to open and close rapidly, and I can experimentally find the frequency to flow rate relationship, then use that mathematical relationship to program variable rate of reduction of pressure. I think the end frequency should be anywhere between 50-100Hz. Can the solenoid valve survive this in the long term? Long term means 5-10 years. Anyone having experience with solenoid valves please let me know.
- Maybe a very specialized/expensive solenoid but not that one, there is too much mass there.
- In the end, what are you trying to do ?
Its a science experiment for which i need to make a flow rate controller. Commercial ones are expensive. I need to change the pressure of a system at a controlled rate.
See I have no way of knowing whether its finally going to be 50Hz or 5Hz. what frequency would you say is safe for this? And why can't this solenoid valve take high frequency?
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It would be impossible to move the heavy metal armature, for the spring (if any) to respond, for the solenoid mechanical stop to survive at 100Hz, yet along to survive for 5/10 years.
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You may run into a resonance situation when trying.
If we reduce the outlet orifice size, the frequency requirement might be reduced.
This is a normally closed type. So when the power is off, it will shut. I guess to control the flow rate, the shut period has to be more than the open period. If we orient it so gravity helps the spring, the valve would shut quickly, in anywhere between 5-50 milliseconds (or is it better if gravity acts against the spring and helps the magnet instead?).
When the magnet is on, it should open instantaneously too.
Do you think its worth trying?
My main concern is, would the magnetic electrical mechanism inside it be able to take the quick on and off? Are we expecting any heating issues and subsequent failure?
The data sheet says Life test 30,000 times (500cc container, 11s/time)
So if you operated it only100 times per day, it would only last 300 days
Needle valves and ball valves could be 'motorized' at low costs.
I do not think your bit bang solenoid control will work in the longer term.
@jim-p that settles it I guess.
@build_1971 I salvaged a needle valve from an old digital sphygmomanometer, but it has constant flow rate. How are you suggesting its output be varied?
Edit, sorry it isn't a needle valve. I just googled needle valves. Mine is just a valve with what i guess is a tiny puncture in it.
There is a good reason for that: they are designed for the purpose, and they last a long time.
I think that valve would work just fine for your project. The picture and description leads me to think it has the plastic tube all the way through to unit. Inside the tube is a spring loaded steel ball that blocks the tube. The solenoid pulls the ball back away from the blocking so the fluid can flow. When the current is interrupted, the pressure and the spring force the ball to block again.
The fluid flow can only be one way, so be sure to do the plumbing correctly.
Do you have any documentation showing your solenoid valve can handle your pressure? Do you have all the necessary plastic tubing and clamps for your project?
I am using silicon tubing and steel clamps. The pressure is handled well. But @jim-p found the data sheet and says that says its life is just 30000 times. At say 100Hz, that would be 6000 times in a minute, and the thing would last just 5 minutes!! Should we trust the data sheet? Did someone actually test it 30000 times or did they just type in a better-be-safe-than-sorry number?
Use Google to see what "mean time to failure" refers to. I suggest a motorized needle valve will last forever. Or buy a real pressure regulator, which is also a needle valve assembly.
Rather than using something like PWM for pressure control (not a terrible idea if you could solve the fast acting valve/pulsation problems) you might consider driving the screw control of a conventional pressure regulator with a stepper motor. Some regulators will require a certain amount of torque so you'd need to consider that when picking your regulator and stepper motor.
few discomforts with that idea.
- That would add too much machinery and designing and calibration.
- The set up would not remember what pressure-reduction-rate is set the next time we power up the system and want to change the pressure-reduction-rate.
- The top and bottom pressure are not constant. Next time say the top pressure is 1200KPa and has to be brought down to say 600Kpa in 19 seconds, all the previous calibration would be useless (i.e, how many turns of the screw).
One thing just came to mind, at different pressures the flow rate would also change for any particular setting of any valve mechanism. For that we would need a flow rate sensor to monitor the flow and make adequate alterations to the valve.
Is this getting too complicated?
I am working with gasses and my tubing is like 3mm. Its already hard finding right connectors, leave alone right size valves or sensors.
With your design, the flow rate is constantly changing, by design? Zero to max and back to zero. What is your plan to smooth the flow rate before measuring it?
You would close the loop on pressure so the number of screw turns would not be used in any calibration since you would just turn the screw backward or forward to achieve the end pressure and there would be no particular need to know how many turns it took. If it's important to know the pressure that was set when the system was powered down, just record that in nonvolatile memory on the controller.
And a standard gas pressure regulator is also a motorized needle valve with a spring loaded diaphragm providing the motor power to adjust the needle. Some will even last for many years and need no external power.
Exactly. The spring and the gas pressure provide the "power" to the regulator and when set to the desired pressure no addition energy is needed to maintain the regulated pressure as long as the supply flow rate is sufficient. I have circled in red on the drawing in post #13 the valve that does the regulation. If the regulator body was transparent you could see the flat part of the valve "floating" back and forth as it regulated the pressure.
CJAV08-2B05A1.pdf (256.8 KB)
And at 100Hz, about five minutes.