Pages: [1]   Go Down
Author Topic: variable air solenoid control  (Read 2736 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Full Member
***
Karma: 0
Posts: 125
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I need to control an air valve variable from 0psi to 150psi (not just on/off).  I don't know the actual volume at this point but it is likely less than 5cfm.  Is there such thing as a variable air solenoid?   Or do I have to use something like a valve connected to a servo?  It needs to respond about as fast as you could move a ball valve by hand if you were to move it quickly.  Also this is a hobby project so cost needs to be kept low.
Logged

Dubuque, Iowa, USA
Offline Offline
Faraday Member
**
Karma: 49
Posts: 2546
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You're looking for a pressure "regulator" to do this. It's the same idea as your valve-connected-to-a-servo scenario, but regulators have a spring loaded ball inside them to control the pressure whereas a valve just opens an orifice.

Any home improvement store should have them for under $10.
Logged

Offline Offline
Full Member
***
Karma: 0
Posts: 125
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

No, I should have expanded a bit more.   The variable air flow is to be controlled by an arduino.  So to simplify, I would read a potentiometer and set the air flow to correspond.  turn the pot all the way to the left and it is at 0 flow.  Turn it all the way to the right and it is at full flow.  Anywhere in between as well.  Set the pot at half way and the valve would be opened half way.
Logged

New Jersey
Offline Offline
Faraday Member
**
Karma: 70
Posts: 3743
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

A little bit of google found this: http://www.grainger.com/Grainger/SPEEDAIRE-Regulator-4ZM08?Pid=search Looks like you could rig up some mechanism with a stepper motor to turn the pressure adjustment knob. I'd assume many others exist.
Logged

Offline Offline
Full Member
***
Karma: 0
Posts: 125
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Yes I've googled quite a bit.  I have found absolutely nothing that already exists as a variable air solenoid.  If such a thing exists it may not be called that however. 
Logged

Pottstown, PA
Offline Offline
Sr. Member
****
Karma: 5
Posts: 323
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I am confused. Are you trying to regulate air flow or air pressure? - Scotty
Logged

Offline Offline
Full Member
***
Karma: 0
Posts: 125
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

flow - sorry if I confused anyone else.
« Last Edit: November 23, 2012, 08:40:19 am by freakdaddy » Logged

Grand Rapids, MI, USA
Offline Offline
Sr. Member
****
Karma: 10
Posts: 282
Yes, I remember
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I would add a servo to something like this http://www.amazon.com/In-Line-Air-Flow-Regulator-Gage/dp/B00173AZ40   as it will likely be a lot cheaper than finding a ready built controllable pressure/airflow regulator.  It won't be supper accurate, but if you add a pressure/flow sensor after the valve you can implement a closed loop controller on the Arduino and probably get fairly good accuracy.

A pressure regulator, like the one I linked above will only control pressure, not air-flow.  Think of it like a voltage regulator.  It will make sure you always have a constant (voltage) pressure on one side, but that will only equate to a constant (current) air-flow if there is a constant resistance involved.  True volumetric airflow valves do exist, but they, like current limiting power supplies, are a lot more complicated and more expensive. 

Alternatively, if you could live with a few discrete airflow options you could build the pneumatic analog of a resistor ladder adc (google that) with a bunch of different sized tubes (resistors) and a handful of solenoid valves.  I probably wouldn't really do it this way, but it sure would be cool if someone did.
Logged

Offline Offline
Full Member
***
Karma: 0
Posts: 125
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Ok thanks.  Low accuracy is ok.  I figured I may have to use a servo and a valve based on the fact that I never found a ready made device on google.
Logged

0
Offline Offline
Tesla Member
***
Karma: 145
Posts: 9699
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Ok thanks.  Low accuracy is ok.  I figured I may have to use a servo and a valve based on the fact that I never found a ready made device on google.

That is probably due to the fact that measuring air flow is not as easy as you think. How are you going to measure the air flow to know if the flow is too high or too low? Perhaps if you gave the details of the intended application there might be easier solutions.
Logged

Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

Offline Offline
Full Member
***
Karma: 0
Posts: 125
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I don't need to measure the flow.  I just need to control it.  It's for a arduino controlled rocket motor!  (actually a compressed air motor)  When the kids throttle up, the valve needs to open and increase air flow proportionally to the throttle position.  If the throttle is at 75% it really doesn't matter exactly what the air flow is as long as it seems reasonably close to the astronaut.  The control is a wireless joystick.  Right now I'm setting up to use a valve and a servo.
Logged

0
Offline Offline
Tesla Member
***
Karma: 145
Posts: 9699
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
Right now I'm setting up to use a valve and a servo.

Probably the easiest way to go.
Logged

Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

Offline Offline
Newbie
*
Karma: 0
Posts: 46
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Electronic proportional flow valves do exist but they're expensive. Some work like you're thinking - basically a stepper operated valve. And others use a PWM signal to control a solenoid valve:

http://www.omega.com/ppt/pptsc.asp?ref=FSV10&Nav=prel03

Would pulsing the air cause any problems for your rocket? Because I was wondering about driving a simple air solenoid with a PWM signal. Higher the duty cycle the more net flow you'll get.

EDIT: Thinking about it, a cheap but relatively fast switching air solenoid may not pulse all that much when driven by a PWM signal. Have a look at this paper:
http://advantech.gr/med07/papers/T06-001-456.pdf
« Last Edit: November 23, 2012, 04:20:03 pm by jabbado » Logged

Pottstown, PA
Offline Offline
Sr. Member
****
Karma: 5
Posts: 323
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Recently had an opportunity to work on a vehicle (Infiniti) that had an Idle Air Control valve with a stepper motor control. Perhaps some automotive devices would work. Not all automotive valves are just open/closed.

- Scotty
Logged

Pages: [1]   Go Up
Jump to: