I am looking for a way to control pressure in a tank. The tank is sealed, and will be generating CO2 (yes, fermentation). I have a pressure sensor reading the head pressure, and wish to control this pressure at a configurable value. A safety mechanical valve is also installed to ensure if this electronic valve fails, I don’t inadvertently create a bomb!
So - has anyone seen a small device that can manage this pressure? Some kind of small control valve? I was even thinking a servo hooked up to some mechanical screw type valve… I also need it to HOLD last value should power be lost (much like a servo).
Are you just asking about a solenoid valve that can be released when pressure hits a certain point? How much pressure are we talking about? There are many pneumatic solenoid valves on eBay that will probably be fine. Depending on flow requirements, I may even have a few in my junk box you could have.
Something like that would work well. Just include a very small orifice on it so that you can release smaller amounts of pressure at a time. You then use a microcontroller to control the valve with a little hysteresis, here is pseudo-code:
int maxPressure = 50;
int minPressure = 40;
if (currentPressure > maxPressure)
{
while (currentPressure > minPressure)
{
OpenReliefValve();
}
CloseReliefValve();
}
Which will keep your tank between 40 and 50 PSI. Then you just need to have some way of measuring the pressure in the tank (plenty of pressure sensors on SparkFun), and thats it. There are valves that have lower supply voltages but you don’t want to connect any of them directly to the pin on a microcontroller.
Edit:
BTW, I’m sure there is some clever guy/gal out there who can give you a schematic to remove the micro controller, or you could also just use an adjustable pressure switch like http://www.automationdirect.com/adc/Sho … 25-1C-D60A to control the valve.
Thanks for your replies - great to see such involvement.
@waltr - I am using Freescale’s range of MEMS pressure transducers. Great sensors that output 0-5V.
@lyndon - I have found a stack of solenoid valves, including these great cheap Lee Miniature Pneumatic Control Valves. I could certainly alter my control output signal to be ON/OFF control, BUT - as the vessel continuously produces CO2, I really need the valve to hold position when power is lost; not drop to it’s normal position (as a solenoid would). So I really need a small mechanically operated valve; something a servo motor would drive. The vessel will allow pressures up to 35psi - the right amount of ‘fizzy factor’ for beer. A safety solenoid PRV will operate at 45psi to prevent the tank from bursting should the control fail.
@RonBeyer - thanks, but I’d really love analog control, or PWM control of a servo motor/valve. ON/OFF solenoids means that if power is lost, the solenoid will either shut off (and then I will rely on my safety valve to protect the tank), or open (which means all my CO2 gets vented). I really need a mechanical valve to just stay put on loss of power.
Sorry it’s not electronically controllable, but Graingers has an adjustable pressure relief valve for less than $10. 20 to 200 PSI. Set one for 35, the other for 45. 1/4" NPT thread.
@lyndon; ahhh nice idea! This should work a treat. Would love to have sanitary tri-clamp fittings, but beggars can’t be choosers!
Just so you guys know, this device will ferment and dispense beer in one unit. Touchscreen Beaglebone will manage pressures and temperatures, and will allow a user to set profiles for temperature/pressure for fermentation and fizziness. HTML interface will mean it can be controlled via smartphones and computers as well as the device.
Anyone with time and inclination - let me know; need all the help I can get. I have the money, just lacking on time at the moment!
I’ve been working on a liquid dispenser (that’s how I found the Open Source Control project) and had the opposite problem: how to guarantee that flow stops if power is interrupted. It was a problem because I wanted to avoid reliability problems with cheap solenoid valves and also be able to manage dispensing with just gravity flow and no pump pressure. So I was working on using R/C servos to make pinch valves. Problem there, of course is that if the servo opens and loses power, it stays in position and flow continues. I finally decided to stick with solenoid valves and deal with the issue of gravity flow solutions later.
A battery backup seems more complicated to me than a motorized ball valve.