# Control the pressure of Hydrogen in a small container without the use of a pressure regulator

I had recently asked this question, and due to the comments and general consensus of safety concerns, I decided to re-ask the question, attacking the problem from another angle.

## The Problem

I need to store a relatively large amount of Hydrogen in a small (12 cc) Aluminum container at about 1000 psi. The problem is not the generation of the hydrogen, nor the transfer of the hydrogen into the container at that high pressure, but how to extract the hydrogen out of the container without using a pressure regulator.

I am afraid that the container is too small for a pressure regulator to fit in it, and the whole device has to be small on the outside, so one cannot fit it on externally...

The output pressure I desire would be about 200 psi

## An Idea: (I'm an Electrical Engineer, don't laugh!)

### Emulate Vapor Pressure

Gasses like CO2, Butane, and Propane have relatively low vapor pressures, allowing them to form a liquid at reasonable pressures. At about 800 psi, CO2 will form a liquid, making it so that any container holding liquid CO2 will let out CO2 at that somewhat constant 800 psi of pressure until there isn't enough CO2 to keep itself in liquid form. Hydrogen, however, will not do this because it's vapor pressure curve is far too sensitive. It would have to be cooled down to some ungodly temperature, which is not an option:

I was wondering if I could somehow emulate this behavior by possible adding something to mix with the hydrogen and change it's vapor pressure. Is this even possible?

### Edit:

Flow rate doesn't directly matter, but the more flow the better.

• Do you want semi-constant output pressure, or semi-constant output flow? What kind of flow rate are you looking for? How constant does the flow rate need to be? Also, you really need to consider hydrogen embrittlement of aluminum and pick the best alloy. – Jon Custer May 9 '16 at 21:59
• Have you explored the range of inline micro pressure relief valves available, or even micro controllers/relief valves for pneumatic applications? Very small footprints. – long May 9 '16 at 22:22
• @JonCuster Constant output pressure. – Nick Pandolfi May 9 '16 at 23:46
• @long It seems to be that the tiny ones only handle tiny pressures. If you have an eye on one please send a link. But that was the first solution I was considering. I have looked far and wide. – Nick Pandolfi May 9 '16 at 23:46
• Would something like H-Cube be interesting? They use water electrolysis to produce hydrogen and can go up to 100 bar. – K_P May 10 '16 at 0:02

## 1 Answer

More like a suggestion than a solution.

First, understand what you are trying to achieve. You are generating hydrogen at some rate and storing it at high pressure. From your previous question I understand that the pressure of your stored $H_{2}$ is only a very general approximation.

Your objective is now to extract $H_{2}$ in a controlled way without using regulator. This sounds absurd.

My complaints:

1. I am very sure that you do not have a pressure gauge to measure the pressure of your $H_{2}$ container. This is a serious design flaw.
2. When you will try to extract $H_{2}$ the flow rate will be really high.

Now to the possible solution:

1. Incorporate atleast one dual valve regulator. This will take care of both issues mentioned above. You will be able to measure container pressure, and regulate flow-rate.

(But you do not want a such a regulator ! okay. What you can do is to get the smallest one possible and connect the regulator using 1/8 inch or 1/4 inch PTFE tubes and keep it separate. The regulator will then need to have custom input connector. It is not difficult to design one. Regulator to tube can be connected using all metal nut-ferrule connection which are safe upto 2000 psi or more. )

Well, your safety should be prime concern than the size of device I guess. In case oxygen leaks in and temperature at some local point is enough there is a chance of SERIOUS explosion amplified by the high pressure.

Some things about which I am concerned:

• Do you evacuate the container before filling $H_{2}$ in ? If not, you are making a mixture of $H_{2}$ and $O_{2}$. Be careful !

• The container of $H_{2}$ can handle high pressure or not. Have you tested it ? You can test it with $N_{2}$ or just air before using $H_{2}$.

• If you need more information about custom connections then send a comment. – ankit7540 May 25 '16 at 9:16