Air Pressure/Volume

[Borja1055]

Hello, I am designing a pressurized air system and i have a simple question. How large of a tank do i need to keep airflow constant in a system that requires 12 PSI at all times and has 8 hoses. Thanks

 

[LittleInch]

I have lots of other simple questions before you get close to an answer

What is the incoming flow?
Is it a steady flow or does it vary?
What is the outgoing flow per hose?
Is it a steady flow or does it vary?
If so by how much?
Are all hoses on at the same time?
If not How does the outflow flow vary over time?
How much leeway do you have on the 12PSI? Note than "None" implies a VERY large tank even +/- 1 psi might need a big volume depending on the answers of the "simple" questions above.

The simple answer - It's as large as you need it to be and whatever size you determine it will either be too big and someone will complain about the size or cost or it's too small and everyone will complain that there isn't enough air at max flow. So make it as big as you can get away with....



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[HPost]

How much air flow and what will the density of the air be?

Also, what diameter will the bore of the hoses be and how rough will the bores be?

And what will the tolerance be on the 12 PSI?

The volume of air flow and its density and the bore size and roughness will give you the pressure loss. The accuracy of the pressure level will dictate what volume you need to store to absorb pressure spikes and supplement the low pressures.

 

[dbill74]

The size of your air reciever tank is going to depend on how often you want to cycle your compressor. Generally speaking you don't want to run your compressor more than 20-25% of the time max with a cycle period of at least 5-10 minutes (the longer the better). That said, the questions Hpost and LittleInch posed are important for determing how quickly you drain the reciever and cycle the compressor.

You will also need to know/decide at what pressure to maintain the receiver. You do not want to maintain your receiver at 12 psi, if you do, the pressure at the hoses will never be 12 psi. I would probably go with 20-30 psig in the receiver. That said how close are the hoses to the receiver? If they are within about 50 feet, a single pressure regulator at the receiver will probably be good for you (set at more than 12 psi). Otherwise consider maintaining 20-30 psi in the distribution piping with 12 psi regulators at the hoses. Note: if you go the route of regulators at the hoses, the distribution piping esentially becomes an extension of the receiver tank.

Word of caution, do NOT try to match compressor size/SCFM capacity to usage capacity or for a short (1 min or less) cycle time. If you do, you will wear out the compressor in a matter of days.

 

[zdas04]

I'm not sure about "a matter of days", but it will shorten the compressor life. I like to see compressor capacity around 4 times demand (i.e., if your load requires 100 SCFM, then you want a 400 CFM compressor).

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[dbill74]

Learned from experience. Had severly undersized receiver (tried to match compressor size to usage). As result compressor was cycling at on/off at least once a minute. Was replacing solenoids or other parts at least once a week until we got an oversized receiver on it.

 

[Borja1055]

Just some clarification:

The air comes in to the tank already at 120 PSI. I need to regulate that and keep it constant so the hoses can inflate to 2PSI. I would want the pressure in those hoses to be around 50 PSI.

I think it has to do with volume flow rate. Any help or formulas you can provide for me would be of great help.

Thanks

 

[rb1957]

how does this new information relate to the 12psi mentioned in the original post ?

what does "so the hoses can inflate to 2PSI. I would want the pressure in those hoses to be around 50 PSI." mean ?

do you have a supply of 120psi air ? temperature ?

i don't think you can regulate the reserviour to 120psi (as a demand takes air for the tank, the pressure will drop, no?).

do you want to regulate the demands to 50psi ?

i think you want to control the air supply (at 120psi) so that you can "top up" the reserviour when needed. so you need to decide on the volume or the reserviour and the regulated pressure (max is 120psi, min is 50psi; so you want to be somewhere in between). i think there are a lot of details in the demands that you need to correctly size the reserviour ...
1) the flow rate into the demands, pressure loss along the hoses ?
2) the flow rate into the reserviour.

i think the problem is more to do with conservation of mass than flow rates. i see it as ...
1) how much air is in the reserviour ?
2) how much can be demanded ?
3) how much can be delivered into the reserviour ?

the supply of air will depend on the pressure difference between the reserviour and the demands. the reserviour wll let air flow out, losing pressure, untill it meets your lower bound (reserviour regulator setting) when more air will be supplied into the tank increasing the pressure again.

another day in paradise, or is paradise one day closer ?