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

 

[EdDanzer]

In pneumatics a pressure reducing valve is called a regulator. All these devices have a seat that closes as the pressure balance is met. The reason I suggested a paintball marker (gun) is these are good to 5,000 psi / 340 bar. You may need two regulators, on for primary pressure reduction (paintball marker) and one for fine control if the flow rates vary much, and you may need a relief valve or relieving regulator if there is much temperature variation when holding pressure.

 

[mk2000]

EdDanzer
I am not specifically looking for a primary stage pressure regulator as such and am trying to avoid primary stage regulator as size and weight are important, however what I was thinking about was orifice which will have a large pressure drop across it. However I am not sure if this is possible as I have not seen an orifice used in such an application before. I hope this clarifies my intent.

 

[EdDanzer]

An orifice will only work if the high pressure never changes pressure, or temperature. If either changes the flow rate will change which will affect the down stream pressure.
More detail about your application will make it easier to provide better suggestions.

 

[mk2000]

EdDanzer
As highlighted in the posting above I am trying to regulate the pressure from a gas cylinder to a tube for human consumption. I need a regulating system to bring the pressure down from the cylinder to a level where it is appropriate for human consumption. However size and weight is a factor therefore trying to avoid a secondary regulator if possible.

I think the orifice is appropriate because the primary pressure drop does not need to be accurate as long as it is with in the range of the input of the secondary regulator. Therefore the variance can be large coming out of the orifice.
The secondary stage regulator will regulate the pressure to the set value.

Let me know if my thinking is correct?

 

[MikeHalloran]

You can buy air in high pressure bottles. But you seem to be proposing separate oxygen and nitrogen bottles. Is it your intention to feed the human some odd or variable N/O mixture? If so, you need at least two regulators and a mixer, and probably a computer.

Is it your intention to just let the gas flow continuously, or do you need a demand flow regulator, like on a scuba pack? An orifice would not serve as a pre- regulator, unless you are prepared to dump the gas that's not being inhaled, continuously. This is because if you stop the flow, the pressure drop across the orifice goes to zero.
The demand flow regulator is less wasteful of expensive compressed gas.

Scuba systems used to have single- stage regulators, with a large diaphragm and mechanism attached to the air bottle, and large low pressure hoses to route the air to the diver.

For decades they have mostly used two-stage regulators, with a small pre-regulator on the bottle, and a demand flow regulator of modest proportions at the diver's mouth. Total volume of this mechanism is a bit smaller than the older system, and it doesn't suffer the problem of the large hoses getting full of nasty tasting gunk.



Mike Halloran
Pembroke Pines, FL, USA

 

[mk2000]

Mike
You asked:
You can buy air in high pressure bottles. But you seem to be proposing separate oxygen and nitrogen bottles. Is it your intention to feed the human some odd or variable N/O mixture? If so, you need at least two regulators and a mixer, and probably a computer.
No this not my intention at all. My intention is to feed constant stream of the gas at constant flow and pressure (to the user).

Is it your intention to just let the gas flow continuously, or do you need a demand flow regulator, like on a scuba pack?
No I my intention is for a continuous flow of gas

An orifice would not serve as a pre- regulator, unless you are prepared to dump the gas that's not being inhaled, continuously. This is because if you stop the flow, the pressure drop across the orifice goes to zero.
I agree. Intend for the gas to flow through the orifice first then the regulator

The demand flow regulator is less wasteful of expensive compressed gas.
agree but in my situation; this is acceptable

Scuba systems used to have single- stage regulators, with a large diaphragm and mechanism attached to the air bottle, and large low pressure hoses to route the air to the diver.
I will be most interested to learn about the mechanism which was used and how it worked. Do you have any references or can you explain how it worked?

For decades they have mostly used two-stage regulators, with a small pre-regulator on the bottle, and a demand flow regulator of modest proportions at the diver's mouth. Total volume of this mechanism is a bit smaller than the older system, and it doesn't suffer the problem of the large hoses getting full of nasty tasting gunk.
I will be interested to learn how design changes influenced resolution of these situation!

I am new in this field and the only experience I have is in design of valves and regulators is in the natural gas and water and at lower pressures. Therefore any info in this area is most welcome and I thank you in advance.

 

[MikeHalloran]

The first stage regulator's design will look familiar, the second stage probably will not:

http://web.mit.edu/scuba-club/

http://www/Everything_about_regulators.pdf

http://entertainment.howstuffworks.com/scuba.htm

Mike Halloran
Pembroke Pines, FL, USA

 

[mk2000]

MikeHalloran

Thanks for the links.

If you have more information it will be fantastic. Especially if you know of any hand books which detail the deferent regulator designs and norms with in the industry.

 

[MikeHalloran]

I think we've pretty much reached the limit of what I know or can find out quickly about gas regulators.

Mike Halloran
Pembroke Pines, FL, USA

 

[surfdancer]

Since flow, weight and size requirements have not been specified, I can only offer rule of thumb guidance...

1. For constant output pressure, you do need a pressure regulator. Any other type of valve would require external feedback or adjustment to control pressure.
2. For this high of a pressure drop, you need to heed manufacturers pressure ratings.
3. Since you are working from cylinder gas (a variable source as the pressure decays as contents are used) you must use multiple stages of regulation or balanced valve design regulators. Not too many options with a balanced valve at those inlet pressures though...
4. Two stage regulators are available where the inlet pressure effect will be almost insignificant.
5. Make sure your regulators are compatible with oxygen. Typical oxygen regulators are free of contaminants, unapproved lubricants and are also typically brass construction.

Hope these guidelines help.