Controlling gas valve automatically?

[Monito]

A friend asked me to automate his roaster, but it uses gas. How can I control the gas valve automatically?

Thanks,

Monito

[PaulM]

I believe there are servo motor operated valves that can be controlled with a PID with a proportional output. You might try searching for "servo" and "gas valve" and maybe "4-20mA."

[PaulM]

Your project has me intrigued! I mentioned the servo approach because I seemed to recall a discussion on alt.coffee where Andy Schecter actually turned up a good valve for that purpose for a reasonable price. I couldn't look it up before, but now that my son is in bed I gave it a shot, but can't find it. 

But I did turn up this discussion, which uses a different approach, but maybe one you could use. Do I recall that you are comfortable with electronics? If so maybe you could even make the scavenged stepper motor approach that is mentioned later in the thread work. I know that people build small CRC CNC routers to machine model plane parts with those things all of the time, so I imagine it would not be too complicated for someone who knows what they are doing. But the OP's approach seemed ingenious to me, and may even be better.

http://groups.google.com/group/alt.coffee/browse_thread/thread/83ede07c36ec20b6/fb5cf6388d920169?lnk=gst&q=stepper#

[hit "expand all" up top to see the whole discussion, that link is the result of a google search and only shows the posts containing the search terms. The original post is what really caught my attention]

That said, having read a little more now, I would guess the ideal solution would be a proportional valve and PID, but as some mentioned in that thread, those valves are not cheap! But there is probably less risk of failure if you buy a good one, and if this project has some budget room maybe that would be worth considering.

Please keep us updated, what a great project! I wish I could be there to see how you work it out.

Paul

[ButtWhiskers]

I got outbid at a live auction today on a box of government surplus goodies that included some gas valve actuators.  To buy them off the shelf (4-20mA ones like Paul is talking about) usually will set you back 500-900 bucks for the really high quality ones.  http://www.hanbayinc.com/  The winner was someone with deep pockets that wanted some of of the other stuff in the box, and who wouldn't take my offer on the actuators.  I anticipate that they will show up on eBay eventually, though.

(I did wind up with 2 boxes of computer parts, 3 laptops, a drafting plotter, and an In Focus projector for under $300.     )

If you are creative, there are infinite other ways to do it.  I saw one made from an inkjet printer, with the belt system that moves the cartridge operating the valve using a BBQ grill valve with a large disk epoxied on.  The printer driver was hacked to respond to PID input somehow.  That was done by a graduate student in Mechanical Engineering who has long since moved away.   

The approach I had planned to use was to use hot tub actuators, which can be found on eBay for reasonable prices most of the time, but I'm still not ready to automate the milkpail until I am certain of the roaster's worthiness.  Here is an example: http://cgi.ebay.com/Jandy-2440-Valve-Actuator-JVA-2440-24v-for-Pools-Spas_W0QQitemZ130235741412QQcmdZViewItem?hash=item130235741412&_trksid=p3286.m14.l1318

[Hananonn]

I was contemplating using the same flame control my Astoria lever Combo has.
The gismo is connected to the pressure gage cutoff, so there is a way to set the response value at the gas tube. Once pressure feedback reaches certain point the flame goes down to a pilot size height. I have not done it yet but I think this could be possible approach.

[PaulM]

Greg, I wonder what you think of that guy's approach on alt.coffee. He split the gas feed after the regulator (it was a BBQ) into two parallel paths, installed a needle valve in one of those paths and adjusted it to provide just enough fuel to keep the burners lit when the other path was blocked, and installed a solenoid valve (on-off), controlled by a ramp/soak PID, on the other path to supply additional gas as necessary based on the TC feedback and the profile, and then brought the two paths back together before they reached the burner.

One would think that that approach might lead to lots of overshoot and undershoot, but the OP claimed good results, or at least results that tracked the PID program. I imagine the key is in the PID programming (particularly response time) and figuring out the right duty cycle for the solenoid valve, and probably the placement of the TC, but I am curious to hear what you think.

[ButtWhiskers]

Greg, I wonder what you think of that guy's approach on alt.coffee. He split the gas feed after the regulator (it was a BBQ) into two parallel paths, installed a needle valve in one of those paths and adjusted it to provide just enough fuel to keep the burners lit when the other path was blocked, and installed a solenoid valve (on-off), controlled by a ramp/soak PID, on the other path to supply additional gas as necessary based on the TC feedback and the profile, and then brought the two paths back together before they reached the burner.

One would think that that approach might lead to lots of overshoot and undershoot, but the OP claimed good results, or at least results that tracked the PID program. I imagine the key is in the PID programming (particularly response time) and figuring out the right duty cycle for the solenoid valve, and probably the placement of the TC, but I am curious to hear what you think.

Good Grief!  I forgot that usenet even existed...  Never been to alt.coffee before, and haven't been active on any usenet group probably since alt.survival and alt.revenge in the late 90's...   They turned into spam and trollfests with little semblance to their original glory, and I found other things to do.   Alt.coffee just might kill me...

There is definitely some great cogitating and experimenting going on out there!  I guess splitting the line and using one half as a pilot light is one way to do it - but with the kind of heavy insulation I use you could even just control the damper via PID and keep the heat on at a constant, controlling the temperature with venting and air flow.  The problems that arise with adjusting a flame and keeping it lit (as is mentioned out there) may be harder to deal with than alternating the venting.  Unfortunately, this is really not my strongest suit, so I'll defer to the guys that excel at this kind of tinkering.

BTW- The stuff out there with using the stepper motor from an inkjet made me laugh - I thought that control the guy at the lab made was unique and original, but it looks like others are/were already doing it!   The engineer that designs many of the systems we use where I work has agreed to help me on my milkpail when I get around to the automation part, so hopefully I'll learn some more when that happens.  Having coffee-loving engineers in the workplace is a valuable and oft-overlooked resource!

I was contemplating using the same flame control my Astoria lever Combo has.
The gismo is connected to the pressure gage cutoff, so there is a way to set the response value at the gas tube. Once pressure feedback reaches certain point the flame goes down to a pilot size height. I have not done it yet but I think this could be possible approach.

Sounds interesting!  Keep us posted!

[Monito]

I wonder what is Ambex using for his equipment?

I will show a picture of my current setup...

I use WAGO models connected to a Linux computer.
It's actually very simple if you have knowledge of Hardware and Software...the funny thing is that I'm the "goto guy" at work for controlling any of the WAGO modules and I never thought of using it for my roaster.  One day I saw how inexpensive the modules are selling on eBay.

Monito

[PaulM]

Good Grief!  I forgot that usenet even existed...  Never been to alt.coffee before, and haven't been active on any usenet group probably since alt.survival and alt.revenge in the late 90's...   They turned into spam and trollfests with little semblance to their original glory, and I found other things to do.   Alt.coffee just might kill me...

Yeah, usenet isn't dead, but it sure smells funny. For all of the reasons you mentioned. And alt.coffee is a wasteland now for the same reasons, though it was fairly active as recently as last year.  Happily most of the really talented folks are over at HB now, and they are still just as talented, and curious, as they were on alt.coffee. That said, for as long as google keeps the usenet archives up we have an outrageously valuable mine of very thoughtful tinkerings to search. Michael Teahan, talking about coffee technologies, once said "everything old is new again." OK, he lifted that quote from like four thousand years ago, but he was right to use it, because it's still true.

An aside, in that thread RandyG said that he was making a go of it with a bottle of LP, and that "If you hear a dull thud and see a bright orange flash, it didn't work..." That's the spirit!

There is definitely some great cogitating and experimenting going on out there!  I guess splitting the line and using one half as a pilot light is one way to do it - but with the kind of heavy insulation I use you could even just control the damper via PID and keep the heat on at a constant, controlling the temperature with venting and air flow.  The problems that arise with adjusting a flame and keeping it lit (as is mentioned out there) may be harder to deal with than alternating the venting.

Sounds like a perfect application for a scavenged stepper!

[barko78]

I wonder what is Ambex using for his equipment?

My Ambex has a Maxitrol valve that is controlled by a Watlow temp. controller.  There also is a manual knob so you can control the flame height, basiclly it sends a mv signal to the maxitrol valve.  All electronic.
It works quite well.

[milowebailey]

The one that a Sonofresco uses is about $100 new from them..  I don't know if that would work for a larger roaster.