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Calculate gallon volume in tank from psi?

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  • Calculate gallon volume in tank from psi?

    I have two 60 gallon tanks or 120 gallons of total storage.

    I have a 50% duty cycle compressor that is rated for 10 minutes of steady use or roughly 10 gallons in that time.

    I would like it to kick on when the combined tanks read 110 gallons, however the solenoid valve doesn't detect how many gallons are in the tank, it only detects how much pressure (PSI) is in the tank.

    So if my only way of turning the compressor on and off is by detecting PSI levels, is there a calculation to know what psi would be in these tanks at 110 gallons for the pair (or 50 gallons for the single) so that I could know what psi I need to set the low end kick on at. Normally it goes from 90-120 psi but I'd imagine I need to set it higher to 100-120 psi or higher.... but this is all just a vague guess without knowing the math calculation to know for sure.

  • #2
    Originally posted by Zoilus View Post
    I have two 60 gallon tanks or 120 gallons of total storage.

    I have a 50% duty cycle compressor that is rated for 10 minutes of steady use or roughly 10 gallons in that time.

    I would like it to kick on when the combined tanks read 110 gallons, however the solenoid valve doesn't detect how many gallons are in the tank, it only detects how much pressure (PSI) is in the tank.

    So if my only way of turning the compressor on and off is by detecting PSI levels, is there a calculation to know what psi would be in these tanks at 110 gallons for the pair (or 50 gallons for the single) so that I could know what psi I need to set the low end kick on at. Normally it goes from 90-120 psi but I'd imagine I need to set it higher to 100-120 psi or higher.... but this is all just a vague guess without knowing the math calculation to know for sure.
    I'm not sure I understand. Are the tanks storing compressed air. Air or any gas ALWAYS fills the space available. You always have 120 gallons of air, the issue is at what pressure and that defines the work the compressed air could do.

    What pressure are the tanks and compressor rated for, what flow is the compressor rated for? I don't think I have enough information to answer the question, but it doesn't sound like your compressor has enough flow (or duty cycle) to do much useful work. What flow and pressure do you need for whatever work you are trying to do with the compressed air.

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    • #3
      It would be compressed oxygen, roughly 90-95% pure medical grade. So not 99-100% pure industrial grade.

      Maybe I'm making this too complex with how I'm talking about it, forget the duty cycle.

      The compressor is: .6 HP (Rated/Running) - 1.2 HP Peak

      1.0 Gallon Steel Tank

      1.60 CFM @ 40 PSI

      1.20 CFM @ 90 PSI

      but I do not have the values for 90-120psi. However I know the value from 40-90 so I'm sure there is a calculation to estimate from 90-120 but I'm just not sure what it is, so I'm not sure the exact cfm or lpm requirements of it above 90psi.

      I do understand that its 120 gallons in the tank regardless, however quite obviously compressed gallons into the tank offer more storage of the oxygen air, that's why welding K or T tanks come at 2,000+ psi since it stores the most volume of oxygen.

      These tanks I have however are not high pressure tanks and I'm not running a high pressure system.
      The tank maxes at 300psi, but we are not going anywhere near that, ever, so I didn't think that was required information.
      The compressor maxes at 120 psi then turns itself off via a
      solenoid valve (that most compressors have) that detects the psi ratio in the tank, to turn on at 90 and off at 120 psi.

      This is being used for a low pressure, high volume system, so while the psi will be low (as in 120psi instead of 2k+) I'll be running 30lpm of 90-95% oxygen from oxygen concentrators to the intake of the compressor to try and keep it as close to "free air" as possible, to prevent a back vacuum by feeding it enough lpm.
      Since I don't know what lpm requirements are going to be from 100-110-119 before it turns off
      I have a 2psi pressure relief valve before the compressor that blows off any extra back pressure into the air.

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      • #4
        At 120 psi, the compressor will handle less than 1.2 cfm, maybe 1 cfm. 1 cfm is 28.3 L/min, 1.2 cfm is about 34 L/min so your feed from oxygen concentrators is in the ball park. If you are using more than lets say 1.2 cfm at 90 psi, the compressor can't keep and the pressure in your big tanks will sag. If you are using less than 1 cfm (estimated) the compressor can keep up; it will top up the pressure to 120 psi, then shut off until the pressure reaches whatever minimum you set and it will cyclse on again.

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