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Proportional flow valves

Proportional flow valves

Proportional flow valves

(OP)
Hi, I was wondering how do i convert one of those solenoid pneumatic 2/2 control valves to a proportional flow pneumatic valve. I was hoping to use a range of 0-5V to determine the flow rate of the valve. I understand that there might be some electronics involved. So far what i have learned is that i use a Pulse width modulated driver and feed in the voltage into it to determine the duty cycle.
The varying duty cycle should determine how much the valve moves in or out. I am not too sure about whether this concept would work.
Can anyone help me with this?
Thanks

RE: Proportional flow valves

Sounds very interesting! I am just going to ask some more questions:
1) Does the 2/2 refer to a two-way two-postion valve, -actually it may be 3-position?
2) How would your pulse width modulation determine duty cycle with voltage being fed in?
3) Are you trying to turn this valve fully off-on and to proportionally control it via the counts on-off? A counter with a feed-back loop using a PLC might be an idea.
Please explain.


ttracewicz@atsspartec.on.ca

RE: Proportional flow valves

(OP)
1) yeap, it refers to a 2 port 2 position valve, one is open and the other closed
2) Burr Brown is giving out demo boards of their PWM driver for solenoids/motor. I've got one of them right now. Basically they enable the duty cycle to be tied to a varying voltage. the input signal should have a range between 0-5V, other ranges can be done with additional components. sorry if i was not clear on this
3) I'm trying to see if it is possible to open the valve in steps, like quarter, half, 3 quarters and then full, closing it repeatedly many times would not be an option if the valve is rather big . Flow would hopefully be in steps also.

I learned that some companies use a PWM signal to control their proportional valves also. Sometimes there is also a feedback loop tied to the circuitry to ensure linearity but on the cheaper models, i think linearity is from selection of the return spring in the solenoid valve.

I was wondering if there had been any success in converting normal 2/2NC valves as proportional valves still cost a bit more.
I did ask one company whether its possible. I think it was Alcon valves in the UK and they said it was not. I checked the ASCO Posiflow valve catalog and saw that some of the internal components were modified for proportional valves. But the overall design was basically the same. Thats why I was wondering if was possible to do so
Thanks

RE: Proportional flow valves

First, are you looking open or closed loop control? if open loop, then you need a low friction valve (lapped spool?) otherwise response to a signal ramping up will be significantly different than a signal ramping down (bad hysteresis). You need a solenoid that produces significantly more force than is required to shift the valve so that it can actually be controlled, and the last problem is the shape of the core, since the magnetic force increases significantly as the gap closes; the valve once it starts to move, tends to move all the way. The proportional valves are not that expensive when you have to deal with all these things.

RE: Proportional flow valves

(OP)
yeaa guess so...it does seem a lot of trouble for just that price. The problem is i'm trying to save my university a bit of money as proportional valves tend to cost a bit more.
Thanks again

RE: Proportional flow valves

Hi, I am working on something very similar and was wondering if anyone might be able to suggest a couple of suppliers for these valves. Thanks.

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