Variable Flow Valve?

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Hi All, This forum is an awesome resource.

I'm building a HERMSish system and I need some advice.

After reading up on what others have done, I was thinking of something like this for the HLT:
-Low Pressure Regulator
-Honeywell Pilot Valve - I think I need an adapter to get this working on low pressure propane.
-Nice big thermocouple
-Pilot Burner
-Banjo-14 with a drilled out orifice to work with LP
-A PID to be discovered later

Firstly, am i even on the right track, that might save further confusion.
Secondly, its bugging me that my fancy PID isn't achieving its full potential while connected to a valve that only supports two states. Has anyone used/found a valve that supports a variable flow rate?

 

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This might work... but not cheap

 

[TriangleIL]

They are really expensive, but a few people, myself included, are using Belimo proportional flow controlled valves in their systems. They are controlled with a variable voltage from 0VDC-10VDC.

Others have found a way to "pulse" opened and closed a valve with short pulses to cause the valve to open more or close more. I am not familiar with this method, so someone else may have to chime in.

 

[scookers]

The way they do it in industry is with a flow meter or a temperature sensor (thermocouple or RTD), a PID controller and control valve. It's not cheap. You need a flow meter or thermocouple to tell the PID what to do. This way it can look at the process value and the set point. This is sent by a 4-20 mA signal from the flow meter transmitter or from the weak signal from current induced by the 2 dissimilar metals in the temperature probe to the PID controller. Next it calculates the error and the new controller output based on the PID tuning parameters that are entered into the controller calculated by the user. Next, it sends out a 4-20 mA signal to the control valve. If it is a pneumatic control valve, you will need an I/P (I to P or Current to Pressure) to go from 4-20 mA to 3-15 psi. This stuff all needs to be calibrated and sized properly for the application you are using it for. This is very involved for someone who doesn't know much about PID control or the basics of fluid dynamics. A PID controller is for more than an on off valve. On/off control is much easier to take care of. If you use on off control, it won't be as smooth, but that's just fine for flame controller on a brewing set up. Should be a way to type in a range for the on off. It should work with the thermocouple signal (an RTD is a much quicker response, though and they aren't that expensive), compare it to the on off parameters and then send out a signal to the solenoid valve. I see that you have a furnace pilot valve. A solenoid valve would work better for your application. It will just take the signal from the controller and open the valve, simple. When it loses signal, it closes. You will need a pilot light in order to have it fire the gas, though, when the solenoid opens. This can be achieved with a piece of bent tubing and a 1/4 turn ball valve. This is not the safest, but if you are constantly monitoring your brewing set up, all you have to do is unplug the controller if anything goes wrong and turn off the gas. Solenoid valves are available through grainger and other sources. So in conclusion, achieving variable flow rates is much more expensive than a clunky on off set up that will work fine in controlling your burner. And I'm not sure if the fancy pilot valve is the best for your application. I hope this helps. If you have any questions, reply and I'll get back with you. I am a chemical engineer so I do this stuff for a living.

-Scookers

 

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scookers - I'm asking if anyone knows of (or has used) a proportional solenoid actuator suitable for liquid propane brewing. I'm hoping that someone here has had success and can share their experience.

 

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TriangleIL- I was able to find some Asco Posiflow valves, it looks like my link didn't work above. A haven't been able to find a belimo that looked appropriate, would you be able to post the model number your using?

 

[TriangleIL]

Sorry D, I shouldn't have replied so late at night. I thought we were talking about variable flow to the pumps and not through your propane lines. I've seen others use those Asco valves and think that is the best way you could go.

 

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I've decided a proportional actuator is unnecessary. I would need to control both gas and oxygen flow for it work.