0
$\begingroup$

I am building a small testing device consisting of a double acting pneumatic cylinder. I am using an existing pneumatic line running at 100 psi and I would like to control the force exerted by the piston on my test sample? My question is whether an electronic 5/3 direction control valve can be used to control the output force of the cylinder, the signal for this valve would be dictated by the readings from a load cell attached to the cylinder rod. This is a cyclic test so i need to ensure that the force remains within the allowable limits across all cycles. In case this is not possible can anyone advice about a proper way of doing it? I don´t require high precision +-5% of variance is accepted. I don´t have a lot of budget so, easy to implement solutions are preferred.

Thank you!

$\endgroup$
0
3
$\begingroup$

No, your 5/3 valve will give you on-off control only.

You need an electric pressure regulator also known as a "proportional valve". Typically these will take a 0 - 10 V or 4 - 20 mA control signal to control the valve. The better ones will have a pressure sensor built in to provide feedback to a built-in controller which will then adjust flow to maintain pressure under varying conditions. An LED readout is common too.

enter image description here

Figure 1. A very nice but expensive SMC electric pressure regulator.

If you add this in before your solenoid valve you will have the same pressure on advance and retract and this will ease your speed / cushioning control. The alternative is to place it on the actuator "advance" line that requires regulation but that means that actuator retraction will be at higher pressure and may make speed control difficult with a noticeable initial jerk on moving home.

If you place it before the valve then bear in mind that the valve may require 1 to 2 bar minimum pressure to move the spool in the valve. If you need to pass low pressures through the valve then you'll probably need a pilot operated valve.

$\endgroup$
2
  • $\begingroup$ Thank you for your advice. You've made my life a ton easier. Much appreciated! $\endgroup$
    – JC ME
    Sep 2 at 6:37
  • $\begingroup$ @PeteW's answer points out that a manual pressure regulator and guage will do the job if you don't need to change pressures programatically. $\endgroup$
    – Transistor
    Sep 2 at 8:20
1
$\begingroup$
  • For a quantitative application, the electronic pressure regulator in Transistor's answer is probably the most appealing other than component cost. (It may still need another valve to move backwards, at least with the regulator shown).
  • You actually can implement hysteresis control with a simple 5/3 valve, since you have the load cell in the loop already. You may need to slow the ramp-up rate, with an orifice, a buffer tank, or both. The tradeoff in speed to realize the 5% accuracy may or may not be acceptable.
  • You can also potentially eliminate paying for the pressure sensor in the electronic regulator, with an electronic (solenoid) proportional valve designed for double acting cylinders. However I'm not sure if this would really save money, since the circuitry to drive it precisely is also a slight inconvenience.
  • The simple 5/3 (or 5/2) valve could be used combined with a mechanical regulator, if the load is always the same. Not sure if you will get your 5% with complete reliability.
  • The simple 5/3 (or 5/2) with direct 100psi can again be used, providing fixed end-to-end motion, but with an adjustable spring coupling to vary the load mechanically. Again presuming the load is always the same. Primitive, but perhaps the simplest of all.
$\endgroup$
1
  • $\begingroup$ Thank you Pete! I appreciate you taking the time to expand upon Transistor's answer. You both have helped tons. Cheers! $\endgroup$
    – JC ME
    Sep 2 at 6:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.