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  1. #1
    Forum Member scbaguy's Avatar
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    Default Cascade vs Total volume for filling cylinders

    I'm looking for information from those departments who have used both a cascade system, and a total volume system, along with their compressor for filling SCBA cylinders.
    What are the pros and cons of each?
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  2. #2
    Forum Member FyredUp's Avatar
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    ADVISORY NOTICE: I AM NOT NOW, NOR HAVE I EVER BEEN A SCOTT SALES REP, FACTORY REP, OR FIRE EQUIPMENT SALES REP. THE VIEWPOINT EXPRESSED HERE IS MINE AND MINE ALONE BASED ON MY EXPERIENCES. YOURS MAY DIFFER.

    Great question. We just received with our 2003 FIRE Act grant money a Scott compressor and 4 bottle cascade system. The compressor is rated at 5000 psi and the bottles are 4500 psi. Our SCBA cylinders are 2216.

    The fill station allows simultaneous filling of 2 bottles at the same time. The panel is simplicity at its finest. There is a valve for each cascade bottle and a valve to control the flow to the cylinders you are filling and a fill pressure setting valve. There is also a valve that lets the compressor fill the cascade bottles. The fill station has a automatic safet valve in the lid that if you forget to close the fill valve automatically stops the flow of air when you open the containment lid.

    Okay having said all that, on to your question. Based on technical data supplied to us we have chosen for everyday use to bulk fill having all the tanks open. Why? 1) Simplicity for the operator, 2) Faster filling with less manual operation of valves, 3) The ability to fill 24 SCBA bottles with the cascade system before the cascade bottles need to be recharged by the compressor.

    If we have a major event and the need to fill more bottles than that arises we will cascade the fill bottles using the valves on the fill station control panel. This would gain us 7 more SCBA bottles before the compressor would have to recharge.

    Of course the compressor is an automatic run sustem that starts at approximately 4200 psi so in theory the system would be filling as we go so there would be the possibility of filling more cylinders as the system recharged itself.

    I hope this helps.

    FyredUp

  3. #3
    Forum Member scbaguy's Avatar
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    We will soon be going from 2216's to 4500's on our SCBA's. When that happens we will be getting a new compressor/fill station. My A.C. asked me to "look into" the pros and cons of each. He was told, and passed on to me, that the new compressors have such a high volume, that the cascade system is not needed, since the compressor can easily keep up with filling 2-4 cylinders at a time.
    OTOH- I have heard that the new compressors fill so fast, and run in such short durations of time and cause excessive wear.

    Any other opinions?

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  4. #4
    Forum Member Bones42's Avatar
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    We use 4500psi bottles, my compressor has 4 6000psi storage bottles and I want to say will fill at 35cfm. I have a 3 position fill station. Can I fill bottles direct from compressor, yes, but I normally don't. Main reason is level of noise from compressor. It's not loud, just makes enough noise that conversation is difficult and it's out in our bays where we are cleaning the rest of the equipment. I'll fill from my cascade bottles, when were done and ready to leave, I turn the compressor back on and let it fill while there is no one around. Doesn't have to be this way, but it's a little bit more considerate to the others in the building.
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  5. #5
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    Get the cascade.

    Working at the compressor is too noisy. Cascades let you fill the cylinders, then leave while the compressor refills the cascade.

    A 6000psi four bottle cascade will fill-if I remember right-36 30 min. 4500psi cylinders from 500psi to full without needing recharge.

    Filling too fast can also leave the cylinder low on air in the end. The bottle heats up during the fill, shows 4500psi, but drops to less than 4000psi when it cools.

    What kind of power supply do you have? If you don't have 3-phase power, you'll be limited to a 10 horsepower motor.

    Today, we filled 30 1-hour 4500psi cylinders from a 21CFM compressor/cascade combination. Niether kept up, the compressor ran the whole time, and we had to settle for between 3500 and 4200psi per cylinder, took 30 minutes.

    If we hade to fill those cylinder straight off the compressor, it would have taken over 2-hours. (we'll be doing that again for the next 3 Mondays if you want to come over to TCC's Fire Training Field and help.)
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  6. #6
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    Default Correction

    According to Hackney's chart, a 600psi cascade will fill 26 4500psi 30 minute SCBAs without neediing refilled.

    http://www.rescueleader.com/pdf/DOT%20Storage.pdf
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    another thought ..??what happens if your power goes out and you need to refill bottles..does your back up power supply have enough butt to supply the compressor..???...get the cascade....!!!!!

  8. #8
    Forum Member scbaguy's Avatar
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    I think there is some misunderstanding of 'total volume', either on my part or other folks.

    As I understand it; Total volume is not filling directly from the compressor. The ONLY difference in cascade,and total volume is in the pipeing.
    As it was explained to me, a total volume system would be as follows:
    You have your compressor, fill station, and a bank of storage cylinders (from 2-6), justlike a cascade system. In the total volume system, the storage bank cylinders are 6000psi. the "plumbing" of the storage cylinders to the fill station is such that all of the storage cylinders are open when filling. The pressure in the filling system is the same in each storage cylinder throughout the filling operation. There is no opening of bottles in sequence to "cascade" the pressure up. You are useing the "Total Volume" of the storage cylinders to fill bottles.
    It was explained to me that this is possible nowadays because the newer compressors on the market now have such a high CFM, and can achieve such a high pressure, that the total volume of the storage cylinders is enough to handle your 'average' filling operation. After the filling operation, you turn on the compressor and re-fill the system just like with a cascade.

    If my understanding of this is wrong, please correct me.

    Does anybody have a system like this?
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  9. #9
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    The Total Volume system you describe sounds like a bulk fill. With 4 6000psi cylinders, you can fill 14 30 minute 4500psi SCBA cylinders. then, you're at the mercy of your compressors CFM. If it fills at 9CFM, it takes 5 minutes to fill a 30 minute cylinder, if it fills at 20cfm, it takes a little over 2 minutes, if you can fill that fast to begin with without getting the cylinders too hot.
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  10. #10
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    Thumbs up

    Originally posted by ScottCook
    The Total Volume system you describe sounds like a bulk fill. With 4 6000psi cylinders, you can fill 14 30 minute 4500psi SCBA cylinders. then, you're at the mercy of your compressors CFM. If it fills at 9CFM, it takes 5 minutes to fill a 30 minute cylinder, if it fills at 20cfm, it takes a little over 2 minutes, if you can fill that fast to begin with without getting the cylinders too hot.
    Scott, your description is 100% correct. The system being sold by Scott Air as described by FyredUp
    The fill station allows simultaneous filling of 2 bottles at the same time. The panel is simplicity at its finest. There is a valve for each cascade bottle and a valve to control the flow to the cylinders you are filling and a fill pressure setting valve. There is also a valve that lets the compressor fill the cascade bottles. The fill station has a automatic safet valve in the lid that if you forget to close the fill valve automatically stops the flow of air when you open the containment lid.

    Okay having said all that, on to your question. Based on technical data supplied to us we have chosen for everyday use to bulk fill having all the tanks open. Why? 1) Simplicity for the operator, 2) Faster filling with less manual operation of valves, 3) The ability to fill 24 SCBA bottles with the cascade system before the cascade bottles need to be recharged by the compressor.
    is what we just ordered. While it's possible to run it in cascade mode, as a practical matter, the bulk mode is the only setting I can ever see using.

    We visited this at a NH site and were quite impressed. Quiet operation and the fill station itself is a dream to operate. I think his 24 bottle figure is a little optimistic for empty bottles. By my math it's probably closer to 13 for a 4 bottle 6,000 PSI storage system.
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  11. #11
    IACOJ Agitator Adze39's Avatar
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    Regarding that chart, are the 4500psi/88cf cyldinders 45 minute or 60 minute cylinders?
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  12. #12
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    depending on who's chart it is:

    44 cuft = 30 minutes
    66 cuft = 45 minutes
    88 cuft = 60 minutes
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  13. #13
    IACOJ Agitator Adze39's Avatar
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    Originally posted by ScottCook
    depending on who's chart it is:
    The one that was linked above.


    -----------------


    I prefer, and teach, cascade over "total" or "bulk" fill. The biggest pro of cascade is you can fill more cylinders than doing bulk. The biggest pro for bulk is that *if* you leave the cylinders open all the time then it is simpler operation for the person who is doing the filling.
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  14. #14
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    Originally posted by Adze39
    The one that was linked above.
    Oops, the 45s are 30s. I've seen the capacities listed on different charts as 44cuft and 45cuft for 30's, and 88cuft and 90cuft for 60s.


    Originally posted by Adze39
    I prefer, and teach, cascade over "total" or "bulk" fill. The biggest pro of cascade is you can fill more cylinders than doing bulk. The biggest pro for bulk is that *if* you leave the cylinders open all the time then it is simpler operation for the person who is doing the filling.
    I agree. Also, it would be simpler to set up as initially as a cascade, then if you wanted, you could use the cascade as a bulk fill. All it would cost is a few extra valves and a few feet of tubing.
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