Blending Stik Question

[scubaholicdave]

I'm finally getting around to building a blending stik and have a question about metering/neadle valves. I'm looking at metering valves on ebay and came across this one. I plan to attach it to my medical regulator, but have concerns about it's O2 compatabilty. Will this play nice with 100 percent O2, or do I need to find on that is O2 clean. The model of this one is a SWAGELOK SS-SS4-EPVH.

Thanks

 

[dannobee]

Looking at the Swagelok catalog reveals that particular valve does not come cleaned for oxygen service. You could always take it apart and clean it yourself.

Since I'm not familiar with your particular setup, may I ask that since you're using a medical O2 regulator, why would you need a needle valve?

 

[scubaholicdave]

I dont know if I truly need one! I'm just trying to replicate the design of the commercal stik and assumed that one would be necessary. Is the valve on the regulator good enough to control the amount of O2 to the stik?

I really don't think I want to try and O2 clean this metering valve. Somehow I doubt its as easy as cleaning a scuba regulator. And it would probably never work right after I took it apart.

 

[oxyhacker]

You don't really need a metering valve if you have an adjustable output regulator, because you can adjust the mix using the regulator output pressure knob. You do need some sort of an orifice, and some builders like to use a needle valve instead of an fixed orifice. The orifice will only be seeing 30-60 psi if the stick is set up right, so it is not absolutely necessary for the valve to be "perfectly" O2 clean if you are using it this way, on the low pressure output side of the regulator
It is, though, desirable to have the valve be lockable, so you can set it and lock it, and use the regulator to adjust flow, going by the output pressure, since this provides quick and easy repeatability. If you adjust using both the needle and the reg, you will have no easy reference point to return to when you start a mix, but will have to start from scratch each time.

The valve, BTW, appears to be what they call an "instrumention valve. Most of these have a very precisely adjustable, but miniscule, flow, which is usually much too little for continuous mixing.