A check valve is essential. I use the cheapo plastic ones from US Plastic. There are brass ones that aren't expensive. Someone here would be able to tell you model# etc...
Kev, I've never used a ceramic diffuser but I do use a reactor. I keep my counter just below half full and don't have trouble with creep in the line.
A check valve is essential, and will keep fluid from passing through the line from the tank toward the rig. However, it does nothing to stop anything from passing through toward the tank - gas, water, or oil.
A reactor contributes about as little back pressure as is possible, so, upon solenoid-on state, there will be little "burst" of CO2 through the bubble counter. You have no worries.
It's those with diffusers that have a potential problem. Diffusers will continue to allow gas to pass through at below the cracking pressure. For example, you can run a rig with an Atomic diffuser at 35 psi (which might be necessary for that particular diffuser to function). However,, while it's operating, you may be able to drop the working pressure down to maybe 25 psi ...and it will still work! However, tomorrow, when the solenoid turns on, 25 psi will not be enough to push anything through the diffuser, and nothing will happen.
The point is that the airline pressure, during solenoid-off, will drop far below the necessary cracking pressure. And when it turns on, there will be a sudden rush of CO2 into the line, potentially shooting the bubble counter fluid into the line.
That's been my experience, anyway.
