PSI flow rates on LP and HP reg hoses

[bubbleheadmoe]

Hi all,

I am looking for information on PSI flow rates for the low and high-pressure hoses coming from the regulator's 1st stage. If I have a low-pressure steel 72 tank, filled to 2250 PSI, with just the first stage connected, what would the PSI be coming out of the low-pressure hose and how fast will the PSI drop? What about the high-pressure hose?

I'm working on a little project with compressed air and this information would help greatly.

Thanks in advance,

Moe

 

[Tom]

Hey Moe - PSI's don't flow. CFM's do. PSI's push 'em. But I think I know what you mean. There is way to much information missing from your question to give you an answer such as "3". But this sounds like an interesting problem. Some factors to consider.

What is the first stage set at? Different brands and models surely have different default settings, and some may have been adjusted.

What size opening is the air flowing out? A large hole will flow all 72 cubic feet very quickly even at low psi. A small hole at 2250 psi could take all afternoon to flow 72 cubic feet.

What flow is available from the tank? If you crack the valve ever so slightly, the pressure gauge after the valve will eventually give an accurate bottle pressure in PSI, but take one breath and you are out of air. The flow from the source can't keep up even though an adequate pressure is available at rest.(with no air moving)

What job is the air doing after it leaves the regulator? An open flow (out a hole and its gone) will drain the bottle faster than a resistance. (using the air to do a job before it exits to the atmosphere)

 

[Tom]

sorry - ran out of room or haven't learned the details of this board yet.

The pressure can never be higher than what is in the bottle, and will start dropping the instant you start flowing air. That is why a bottle is filled more than what the regulator is set to. You will have a stable flow until the bottle pressure equals the regulator setting. Then the final output starts dropping until the bottle is empty.

With a good, accurate regulator, a smaller high pressure bottle will be more stable than a larger low pressure bottle holding the same cubic feet when full.

Lots of neat stuff to think about. Tell me a little more about your project. You got me thinking now and this might be fun.

Tom

 

[bubbleheadmoe]

Thanks Tom,

I see what you mean. if you are considering air a gas and not a liquid. Let me explain what I'm trying to do...

I have found a company that makes waterproof hydraulic motors. While these motors usually run on fluid pressure, they can also be run by air pressure. I am experimenting with building an air powered diver propultion vehicle using a steel tank as the air supply. In order to determine what motor to use, the manufacturer needs to know what regulated psi the motor will run (60 or 80 psi), and what amount of torque is required. I am still deciding on what prop to use but I want to make sure that I can get at least 60 psi regulated from a low pressure hose off the 1st stage. And will the flow rate be enough to run the motor for 45-60 minutes. I haven't decided on a 1st stage to use, so general information is what I'm looking for.

Thanks,
Moe

 

[herman]

Hi Moe,
The other question you need to ask the company is "what is the required flow rate of the motor" you are thinking about using. It will be rated in CFM, cubic feet per minute. I suspect ( guess) that it will be in the 2 to 6 cfm range. Assuming 4 cfm, an 80 would give you 20 minutes AT THE SURFACE. Without getting into detail, you know that you use twice as much air at 33 ft that the surface and 4 times as much at 100 ft and an air operated motor will also, after all that's what we are. In other words, if your motor will operate for 20 minutes at the surface, it will operate for only 5 minutes at 100 ft. Something to consider, hope this helps.

 

[Mario S Caner]

Moe,
One other thing you can look into is the possibility of the DOT approving composite cylinder use for your application. Through a source at US Divers(a few years ago) I found out that it hit some snags here in the US, but they were hopeful enough to have pricing structures worked out...

Anyway, the composite cylinder has a working pressure of well over 4200psi, so therefore the size of a 120cu/ft cylinder will be roughly the size of a standard 80cu/ft aluminum cylinder, enabling 50% more air without having to carry around the extra bulk.

Mario

 

[Iguana Don]

Moe,
Graingers, has "air motors", these are specifically designed to run on air & come in different cfm flow rates & hp.
You might want to check it out.
http://www.grainger.com
This might help.
Don

 

[Norm]

As you know, most regs operate with an intermediate pressure of around 125 - 145 psi. They CAN be regulated down even more. I'll bet that your biggest obsticle to overcome will be freeze up of the first stage, as well as capactiy of the tank. Good luck!
Norm

 

[Rick Murchison]

Moe,
What you propose is already in production.
see
http://www.drtomorrow.com/lessons/lessons7/26.html
good luck.
Rick