CO2 valve question

Open 1/4 turn or all the way and why?

You talking on top of the cylinder?

You have to fully backseat the valve (snug, not cranked down) to prevent gas from leaking past the valve stem.

Yes, I was referring to on top of the cylinder. I read somewhere to only open the valve 1/4 turn to get the CO2 pressure. By backseating, you mean open all the way to the stop, but not force it?

Thanks!

I posted a response to this previously. I copied and pasted here instead of retyping the whole thing.

I was always told that if you open all the way to the back seat, you will compress the packing around the stem of the valve and cause a leak over time. Thus you should always open all the way gently and close it a 1/4 turn.

Click to expand...

That is not correct. There are two basic types of cylinder valves used for compressed gas cylinder valves -
packed valves and diaphragm valves. Packed valves come in 2 different types: pressure seal valve (backseating packed valve) and the nonbackseating packed valve.

Diaphragm valves are used for highly toxic gases and high purity gases (I use this type of valve for lithium bromide absorption refrigeration systems). Nonbackseating packed valves are used for corrosive and reactive gases (I use this type of valve for standard refrigerant systems). Backseating packed valves, also known as pressure seal valves, are used for inert gases such as CO2, nitrogen(N2), and also for O2 and H2.

Pressure seal valves, like those on a CO2 tank, must be in the fully open position and snugged, not cranked against the backseat. This pulls the lower stem up to the upper stem driving the upper stem seal ridge to the packing ring, improving the seal and reducing the chance for a leak. This is called “backseating”. See photo below:

John



FWIW, the valves on propane tanks are not double seated. They are of the nonbackseating packed valve style. The valve stems are sealed whether 1/4 turn open or full open.