I'm currently planning out my automated brewery and am debating between biting the bullet on some KLD valves or being patient and waiting for great deals on pneumatic valves (I've been lurking on ebay for ITT valves in the sub-$100 range for weeks now).
Anybody here with pneumatic valve experience? Here are my understandings, so feel free to correct me if I'm wrong.
- I need a solenoid manifold in my control panel. Looks like these are pretty readily available on ebay for fairly cheap.
- I would supply enough air pressure from my air compressor (already have a large one) to actuate the valves.
- Each solenoid would connect to one valve.
- (here's where it gets fuzzy for me) When the solenoid coil is powered, air flows into the actuator of the diaphragm valve, pushing the spring up, and opening the valve.
- When power to the solenoid coil is lost, the solenoid closes and the pressure holding the spring up in the actuator is released, causing the spring to close the valve (and the released pressure flows back through the tube and out of the solenoid manifold exhaust port?)
As far as proportional pneumatic valves go, I'm pretty lost. I see that there are some actuator attachments (called positioners) that allow for non-binary valve actuation, but they are not quite as common on ebay, and are rather expensive. Would it be possible to modify the actuation percentage of a valve by supplying a variable amount of pressure to the actuator? My idea for implementing this is, for each proportional valve:
- Determine at what PSI the valve is fully closed
- Determine at what PSI the valve is fully open
- On the air line to the valve, install a solenoid that can be controlled with PWM to open partially
- Install a cross after the solenoid, with the remaining three directions going to:
- The valve actuator
- A pressure sensor, able to read between the two pressure extremes
- Another solenoid valve, able to be controlled with PWM to partially open, to be used as an exhaust solenoid
With this setup, a PID controller would be used to set the desired open percentage, which would use the pressure sensor output as the input device, and would increase or decrease the pressure by partially opening the input or exhaust solenoids respectively. I don't know if any of this is feasible, as my experience with pneumatics is nil. If it's possible it's sure to be much cheaper than acquiring one of these pneumatic actuator positioners.
Thanks in advance, and cheers!
Hi. You can certainly use pneumatic valves for on/off units. Yes, there is technically more complexity than using all electric, but if the net costs are worthwhile, go for it.
That said... I highly suggest you do not try to modulate any proportional valve with pneumatic control. Air is compressible which makes fine control difficult... impossible in a practical sense. Use controls which are purpose suited when it comes to modulation or valves or other devices.