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Dual stage regulators

M

mjbarnard

Member
Joined
12 May 2010
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48
Location
West London
I understand there is a difference between dual gauge and dual stage regulators (one has two gauges for high and reduced pressure and the other reduces the pressure in two stages).

http://www.barrreport.com/showthread.php/7278-A-Primer-for-Pressurized-CO2

I find regulators suitable for uk are usually labelled dual gauge without any indication whether they might be dual stage as well. Looking at the size of them, many cannot be.

Can anyone point me in the direction of where I might purchase dual stage regulator? Or any recommendations?

Many thanks
matthew
 
Hi,
At the end of the day, all you're really interested in is whether you can control the output pressure to anywhere between 1-3 Bar. The second stage of the of the regulator is controlled by the needle valve. You can see an example of a typical dual stage regulator here=> AquEssentials Dual Stage Reg If you click on and enlarge the image, you can see on the far left of this sample a chrome knurled knob, just above the solenoid assembly. If you can't identify the needle valve on a sample then the next best method of identification is to see the range of pressures on the second gauge. The range should be somewhere around 0-10 Bar. This low range implies that you are able to control the output pressure to this level and that there is likely to be a low range output stage.

Cheers,
 
Clive thank you very much for your reply. I have to admit I am still a bit confused.

The needle valve fine tunes the flow from the output of the regulator. So I dont understand why the presence or absence of a needle valve will indicate a one stage or two stage regulator. Reading the forums it would appear that in North America it is common for needle valves to be provided separately from regulators. Looking at European products they seem more often to be combined. Given a wide variety in quality of needle valves, this may or may not be desirable according to ones viewpoint.

I also do not understand how the pressure range on the second gauge definitely indicates one or two stage pressure regulator. The first gauge demonstrates pressure on the inlet to the regulator. The second gauge shows the outlet pressure (surely whether one or two stage?).

The issues for me around a two stage regulator do not necessarily focus on what output pressure can be obtained - but more on whether the output pressure will remain constant given a varying inlet pressure. This to me is the advantage of two stage over one stage regulators - with associated implications for end of tank dumping etc.

As an anesthesiologist with daily experience of gas cylinders, regulators and flow meters (what we call flow needles), I understand the relationship between the components. I do not though understand why the presence of a flow meter or a suitable scale on the outlet pressure gauge indicates the presence of a one or two stage regulator. In the medical field we would simply need to be told whether regulator was one or two stage. We could not surmise it from it's appearance - with the exception of bulky regulators where there are obviously two components. I would be grateful for your advice.
 
Hi mate,
I think you're expecting too much from these regulators. Industrial gas cylinders are not really that sophisticated, certainly not nearly as sophisticated as the gear you work with. As you're probably aware, the cylinder contains liquid CO2 which outputs the vapor at thousands of PSI (fire extinguishers have a smaller range and lower values). The first stage drops the pressure to hundreds of PSI but there is really no control. The needle valve stage is where the final working pressure of 0-10 Bar is accomplished. If you don't have a needle valve then the range of the output pressure is in hundreds of Bar. The needle valve down-regulates to lower pressures, that's all. 1.5 to about 3 Bar is all we use in CO2 injection, whereas for welding or other industrial applications the working pressures are much higher.

These regulators are adaptations of the welding regulators. They are nothing special and in fact they do need constant attention because the cheaper ones do lower the output pressure slightly as the cylinder empties. In any case, the fact that a regulator has a low range output gauge implies that the assembly is fitted with a needle valve, that's all. If the output gauge was a much higher range that would be a clue that the needle valve isn't installed.

Cheers,
 
A single stage regulator has one regulating mechanism which reduces the cylinder pressure from around 55-60 bar to 1-2 bar in one stage. The needle valve then fine tunes the output flow. A dual stage regulator is easily recognisable because it's much larger and often appears to be two regulators in one - which is exactly what it is. A dual stage has two regulating mechanisms which reduce the cylinder pressure in two stages. The first stage is preset and reduces the cylinder pressure from 55-60 bar down to somewhere around 5-10 bar. The second stage then reduces from 5-10 bar to the required 1-2 bar working pressure. Again, the needle valve then fine tunes the output flow. A needle valve doesn't affect the output pressure.

If you search google for single and dual stage regulators, the difference in appearance will jump out at you. None of the aquarium regulators sold by Dennerle, JBL, Lunapet, TMC, D-D, or anyone else I know of, are dual stage. If it isn't marked as dual-stage, multi-stage, two-stage, or some variation of that, you can be fairly positive it isn't; but I've seen some aquarium regulators marked as dual stage when they're simply dual gauge, so you have to be careful about that.

In a single stage, any fluctuation of the cylinder pressure results in a slight change to the output pressure, with resulting erratic flow from the needle valve. In a dual stage, fluctuations in cylinder pressure shouldn't affect the output pressure until the cylinder pressure falls below the preset 5-10 bar, by which point the cylinder is almost empty anyway. Dual stage regs can seem like overkill, but they're invaluable if you want a reg that you can set and forget. Provided you change the cylinder before it's completely empty, you should rarely have to touch the reg or needle valve at all once you get the settings how you want them. That's why they're used in hospitals where a change in gas flow could be fatal... just as they can be for our fish and plants.

If you want a fairly cheap UK-made dual stage, CS Milne sell them for £55. Personally I'd look on eBay, though. I recently bought a used Harris dual-stage from America for £80 including shipping. Surplus lab stock in near perfect condition. It would have cost something like £500 to buy a brand new one.
 
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