Precision pressure control of Oxygen and Nitrogen gas 2

[mk2000]

Hello

I am trying to bring a pressure of Nitrogen or Oxygen gas from around the 300Bar relative (4351.1Psi) to just over the atmospheric pressures. To do this the first thing that came to mind was to use a needle valve. However I am not sure if this is the best way to go?
I am trying to keep the weight and size to minimum. Therefore I am trying to avoid using any intermediary pressures reducers if possible. I don’t know of any valves which will operate over such a large range, if you know of any please let me know.
Also if anyone knows any other ways of doing this please let me know.

Thank you

 

[israelkk]

Look at divers scuba gear they have a pressure regulator that reduces the pressure from 300 bar to almost atmospheric pressure.

 

[JLSeagull]

Some of the analyzer pressure regulators such as GO can do this for small flow rates. However, there is no mention of the volumetric flow in the post. One solution would satisfy 1/4" OD tubing, a different solution would apply to 8 NPS pipe. BTW, the solution for oxygen could be very different than for nitrogen.

 

[zdas04]

Trying to do it with a needle valve is pretty tough. As pressure in the tank drops you'll have a smaller dP across the valve and therefore a smaller flow rate. The needle valve would require constant adjustment, like you get from any number of regulators. For single-human size flow rates, the diver's regulator above is a good solution. For larger flow rates I'd look at Fisher or Norseal regulators.

The only thing good to say about trying to do it with needle valves is your capital is lower, but you need constant vigilance to maintain a constant downstream pressure.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[JimCasey]

>> As pressure in the tank drops you'll have a smaller dP across the valve and therefore a smaller flow rate. <<
Splitting hairs: The drop will be critical thus independent of P2. You'll still get a decaying flowrate with a fixed position of a needle valve when the tank pressure decays, just because the P1 decreases.

The regulators that come on compressed gas bottles do just the task that is being requested. AND they are certified oil-free if rated for use on oxygen.

 

[dcasto]

why not use regulators designed for n2 & o2 bottles. You must also becareful with o2 regulators they must not contain oil based lubricants.

 

[mk2000]

Thank you all for your reply you have been most helpful. I took israelkk’s advice and went to the local dive shop and asked about their regulators. They were quite bulky compared to what I needed. But I think I have to live with this for my functional tests. I thank zdas04 for reminding me about the variable pressure if I use a needle valve. However to shade some more light on the situation the flow rates I am looking for is quite small in the vicinity of 4 L/min ( approx. 0.14 cubic feet/min).
From the research I have conducted (google and local dive shop) it looks like I have to design some thing my self if I need to bring the size and weight down to what I need. If anyone know any good references in the area let me know.
Thank you

 

[MikeHalloran]

You still haven't defined what you mean by "precision" wrt to the pressure you wish to maintain. I mention it because precision regulators are usually physically larger than 'regular' regulators.

If you seriously intend to design your own regulator, you will need to buy a book or two.

But even before doing that, search for free literature on safe handling of oxygen. It may contain some surprises.



Mike Halloran
Pembroke Pines, FL, USA

 

[BigInch]

Any medical equipment shop will have oil/grease free regulators for the O2 supply.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[zdas04]

JimCasey,
Flow across a nearly closed needle-valve seat is considerably more complex than simply opening a hole between a high-pressure source and a low pressure sink. With the length of the seat you get a definate pressure gradient over the distance. The pressure gradient will often (some would say usually) cause the flow to never see enough dP at any given point to put you in critical flow at that point. I've seen very small upstream pressure changes have a significant impact on the volume flow rate out a needle valve when it is throttled very close to shut.

David

 

[unclesyd]

Take a look at this type valve (MPV-10K). We used this one and several others of like functions for very low high pressure flows.

http://www.4condec.com/pressure/pressure2.html#Precision_Valve

 

[unclesyd]

Per chance are you trying to mix one of the diving gases, Nitrox, Heliox, Trimix, etc.

I must caution as I know of two fatalities associated with supposedly off standard mixtures of these gases. Even though the mixing of these gases is straightforward there are several input variables that can complicate the calculations. A gas mixture computer is almost a necessity.

 

[mk2000]

MikeHalloran; by percussion I mean input pressure drops from 300 Bar to around 2 Bar (over long time maybe days) and output pressure of below 0.5 Bar is maintained. Pressure drop of 1.5 Bar across the regulator is an assumption as I don’t have the specification of such device yet.

Unclesyd; I am not trying to mix diving gases but my application is similar to diving applications, hence my trip down to the local dive shops. If there are any guidelines regarding oxygen or nitrogen handling please let me know, web links will be fantastic.

Thanks you all as your input has been invaluable, especially with the links and suggestion of suppliers.
Happy New Year!

 

[unclesyd]

My memory recalled these two sites. I have other information if I can get my computer going.

http://www.cisatlantic.com/trimix/tools.htm

https://secure.gue.com/catalog/order/software.shtml

 

[unclesyd]

If you will need any quantity over a period of time you should take a look at a membrane separation system (21%-40% O2), like the Nuvair. This is one of sveral on the market.

http://www.northshorecompressor.com/nitrox.html

 

[mk2000]

Inclesyd; I had a look at the northshore compressor website. What they had looked bulky and I don't think I am able to compact the device in to miniature size. Unless you know of a way.
Thank you.

 

[unclesyd]

If you look at the home base you will see that the membrane portion of the system is quite small. One of the determinants of the membrane size is the required flow so there is a possibility of reduction in size here. No matter what your approach you will still have to have the HP bottles with or without a compressor.

Can you comeback with a little more information about what you are trying to accomplish.

http://www.nuvair.com/shopsite_sc/store/html/nitrox_traveler.shtml

 

[unclesyd]

You also might want to take a look at the "Nitrox Stik".

For information you need to contact the following company.

http://www.envirodive.com/nitroxinfo.php

 

[EdDanzer]

You could try a pressure regulator for a paintball marker, they are small and light weight. Also look at

http://www.beswick.com/

 

[mk2000]

EdDanzer; I have already sent an email to these people and am waiting for their feedback. Their regulators do look promising however the input pressure is lower than what I require (approx 300bar). I am considering placing a pressure reducing valve or something like that to bring down the pressure to a lower range so that I can use their regulator. Thanks you for the link.
I am not quite sure if such a thing as pressure reducing valve exist? A restriction which has a large pressure drop across it (200-250 bar)? If anyone know of such a device please let me know. Otherwise does anyone know how to build one? I can think of a few ways to achieve this but I will be experimenting.
Thank you and regards