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Re: Regulator & Needle Valve Specs & Selection

> Date: Mon, 11 Sep 2000 11:59:43 -0500
> From: "James Purchase" <jpurch at interlog_com>
> Hopefully, if I you can extend your patience just a tad more, I'd like to
> present some "specs" and ask some questions which might shed some light on
> the issues.

Since you didn't specifically limit input to only those holding a BSVR (Bachelor 
of Science in Valves and Regulators), I'll answer from an Experienced CO2 User 

I'll reverse the order of your questions, since that may help arrive at a 
practical solution.

> C. Needle Valve Specs & Selection:
> When I look at the spec sheets of various needle valves, I see  things like
> Maximum Working Pressure, Flow Coefficient (Cv) and Stem Taper Angle and
> whether or not the valve is capable of cutting off the flow of gas
> completely. For example. using the spec sheets for the various valves from
> Nupro:
> Model        Max Working    Cv    Stem Taper   Capable of Cutoff
> Service?        Pressure
> Nupro 31       5000 psig   0.04
> Series Union Bonnet
> Nupro BMG       350 psig   0.019     3 degrees  metering
> Nupro BMRG      350 psig   0.30     20 degrees  regulating
> Nupro BMW       700 psig   0.019     3 degrees  metering
> Nupro BMRW      700 psig   0.30     20 degrees  regulating
> Nupro L        1000 psig   0.15      5 degrees  can be used for cutoff service
> Nupro M        1000 psig   0.03      3 degrees  not designed for cutoff 
> Nupro S        2000 psig   0.004     1 degree   not designed for cutoff 
> Questions:
> 1. Other than price differences, is there a reason why you would select one
> valve over another for our purposes?

The end use is the primary concern.  You want low flow, so the valve with the 
smallest Cv is the best, as long as it's not *too* slow. The Cv is like 
resistance - the smaller the Cv, the higher the resistance to flow.  Inlet 
pressure is a concern if you want to avoid the cost of a regulator. Typical CO2 
tank pressure is 950 psi - it goes higher if the tank is warmer. A Max Working 
Pressure of 1000 psi (without a regulator) might be asking for trouble. 

I don't know how the Stem Taper angle affects things buty I would guess a 3 
degree taper is more needle-valve-like than a 20 degree taper. And more 
needle-like seems to give more flow restriction.  

> 2. Which "specs" should we be looking at, and what ranges are useful and/or
> practical for our purposes?

The Nupro M series (Cv=0.03) gives you a max of 1.2 cubic feet per minute 
connected to an inlet pressure of 2 bar (35 psig).  The Nupro S series 
(Cv=0.004) gives you a max of 0.15 cubic feet per minute connected to an inlet 
pressure of 2 bar (35 psig).  I use the M series and that provides a good 
bubbles/sec range. The BMG and S would give a finer range but may cost more.   

Since the flow is spec'ed at 35 psig, I would *assume* that is a good inlet 
pressure to shoot for.
> 3. Are there other considerations that I'm missing?

Cost, fitting sizes to match the rest of the plumbing, ease of adjustment 
(vernier or coarse), adjustment locking, corrosion resistance, sensitivity to 
blockage (I would guess most fine valves are *very* sensitive), ease of cleaning 
if blocked, colors avilable to match your other components. 

[Special thanks to Marque Crozman of Australia for providing this detailed info, 
archived on my web site ("CO2/Nupro Valve FAQ").

> B. Regulator Outlet Pressure Range:
> Looking at the information available online from Air Products, their General
> Purpose, Single Stage Regulator (dual Gauge has the following specs:
> Model             1   2     3    4     5      6    7      8
> E11-215A (CGA) 3000  15   280   85  0-3000  100   0-30    1
> E11-215B (CGA) 3000  50   850  250  0-3000  100   0-60    2
> E11-215D (CGA) 3000 100  1500  250  0-3000  100  0-200    5
> E11-215F (CGA) 3000 250  1950  350  0-3000  100  0-400   10
> 1 - Maximum Inlet Pressure (psig)
> 2 - Maximum Outlet Pressure (psig)
> 3 - Capacity (scfh at Maximum Delivery Pressure)
> 4 - Relief Valve Setting (psig)
> 5 - Inlet Gauge Range (psig)
> 6 - Inlet Gauge Graduation (psig)
> 7 - Delivery Gauge Range (psig)
> 8 - Delivery Gauge Graduation (psig)
> Questions:
> 1. Assuming the setup of a Reulator + Needle Valve, which of these models
> would be most suitable for our sort of use, and WHY?

We want around 35 psig on the inlet to the needle valve, so E11-215B looks like 
the optimum. Max flow is irrelevant (the valve max is 70 scfh). The "B" model 
gives us the best low pressure valve resolution. But all would work just fine. 

> A. - Gass Grade & Regulator Construction:
> On the BOC Gases web site, they have a chart which is supposed to help you
> select the correct regulator for different gases. Under CO2, they list three
> "grades" of purity and there are two different regulator models recommended,
> depending upon the grade of gas you use.
> Grade of CO2                           Regulator Model
> Recommended
> Research Grade 99.999%                       BHS500/270
> Instrument (Coleman) Grade 99.99%            BHS500/270
> Bone Dry 99.8%                                   BGS270
> The BGS270 is described as constructed from chrome plated forged brass. The
> BHS500 is constructed from chrome plated brass bar stock, while the BHS270
> is chrome plated forged brass.
> Questions:
> 1. Does it make any difference if the regulator is made from forged brass or
> brass bar stock?

If the other specs are equivalent, I would guess not. Perhaps forged is better 
in a severe environment (rough handling). 

> 2. Is there any specific reason why they would recommend a different
> regulator for CO2 of differing purity?

I guess it has to do with the "impurity". For our use, I would say it doesn't 
matter. I can't see how a few PPM of impurity would affect the regulator unless 
it was corrosive or somehow damaging to the internals.  

> 3. Are the "beer tap" regulators so many of you are using capable of being
> used with the wide variety of "grades" of CO2 which seem to be available
> (i.e. "Industrial/Welding", Medical, Food Grade, etc).

I think most CO2 supply stores use "Food grade". Again, for our use, it doesn't 

> 4. Is there a real difference here?


George Booth in Ft. Collins, Colorado (booth at frii_com)