I want to thank Marque Crozman of Australia for creating this Nupro valve FAQ. I think it covers just about everyhting you would want to know!
More information on the Nupro valves. They are made by a US company called Nupro, whose parent company is Swagelock, who make a lot of pressure valves, connectors and hosing. (you can virtually buy all gas fittings from them for your CO2 system at a price less of that of Dupla)
The Nupro valve you have listed is not the smallest one they have available. The one you have listed, they quote as being their "M series" valve and have a max Cv rating of 0.03. This rating is like the equivalent of resistance. Which, according to their data sheet, translates to a flow rate of 1.2 cubic feet per minute when connected to an inlet pressure of 2 bar (35psig).
The linearity of the valve is also pretty linear, with a slight kink at the bottom end, approx 5% off being linear (kink only lasts for the length of the first turn). The valve has a total number of turns to open of 8-10.
The reason for the variation, is because this depends on the minimum open setting. The valve, which by the way is not refered to as a needle valve, but rather as a metering valve, so I suggest that when people go to by a valve from a valve and fitting company, they might have better luck finding the right sort of valve by asking for a metering valve.
These type of valves are not designed as shutoff valves, so some sort of shutoff valve should be included, if you want to switch off the flow. (Although this could be done by winding down the regulator) What I have done is installed my solenoid valve before it, so use that to shut it off. This also has a manual override, so that you don't have to power up the solenoid if you don't want to.
They do have a smaller valve, which is listed as being the "S series". This has a max Cv rating of 0.004, which at the same inlet pressure of 2 bar (35psig), translates to a maximum flow rate of 0.15 cubic feet per minute. This valve has a number of turns till open of 8-12. It also has a larger kink (as expected) at the lower end, but becomes almost completely linear from the third turn onwards.
There is also an "L series" that is bigger again than the "M series" with a max Cv of 0.15
The only difference in the labeling between the one you list and the smaller one, is that you replace the M, with an S.
The M and S series valves come in both 1/8" and 1/4" fitting sizes and are available in 316 stainless steel, brass (cheapest and suitable for CO2), and alloy 400. They can withstand pressures up to 2000psig or (137 bar), are panel mountable and have three options of handles, vernier (mmmmm), fine adjustment and slotted.
The handle has two allen key slots, one is used for setting the minimum flow, and the other is to lock the handle at a particular setting, useful if there is the possibility of it getting bumped, or affected by children etc.
The version I bought is labelled as B-SS4 (The B stands for brass and the 4 stands for 1/4") The 1/8" version is labelled as B-SS2.
The valve comes standard with fine adjustment handle, but the vernier to go with it, adds a -VH to the labelling, so the one I bought is then labelled B-SS4-VH.
The version you refer to is labeled B-4MG, which is a 1/4" fitting version of the "M series", a 1/8" version of the same is labelled B-2MG. Again, adding a -VH turns it into the vernier version.
The valve is fantastic, allowing me total extremely fine control over my CO2 flow rate. I can wind the rate from about 1 bubble every 5 minutes, to about 4-5 bubbles a second, linearly, if the inlet pressure remains constant. Changing the inlet pressure allows me a greater control range.
In Australia, I bought the valve from
Brisbane valve and fitting pty ltd, 60 commercial road, Newstead, Queensland. Tel: 07 3252 8900
and it cost me AU$77.25 for the valve (B-SS4), and AU$29.75 for the vernier.