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How do you determine the blower size to overcome pressure

  1. Nov 3, 2015 #1
    Known: Heater intake is 1/8", output is 1/4", pressure drop is ~8.3 psig at 5 CFM flow. Minimum SCFM is 1. The blower would need to put out a minimum of 1 SCFM and be variable above that to a max of 5.3 CFM

    How do I determine what size blower I would need to overcome this pressure and obtain 5+ CFM flow? I cannot use compressed air.

    Any formulas (obviously a non-physics/engineering person here) that could help here would be appreciated. Any other places you could point me to would be appreciated as well. If you can help, please do.
  2. jcsd
  3. Nov 4, 2015 #2


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    Gold Member

    hmm, trying to get 5.3 CFM through 1/8" intake, the average air velocity is 315 m/s and maximum will be above the speed of sound. Can you make the opening bigger?
    No wonder you need 8 psi to get the air through. Definitely, no blower can do that. I would suggest using a piston or diaphragm pump. You would have to check the flow vs pressure specs for the various pumps. These are available from pump manufacturers.
  4. Nov 5, 2015 #3


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    Staff: Mentor

    This isn't an issue to be calculated with a formula. You have a performance requirement, so you need to be looking at performance capabilities of real products in catalogues or speaking to vendors about what they have that meets your needs. That said:
    There is no hard line between "compressor" and "blower" as both generate pressure to move air, however typically at the airflow and pressure you are looking for, vendors would call that a "compressor", not a "blower" and you will need to be googling for/asking for the right thing to get matched with what you need. So it sounds to me like you need a low pressure compressor, with a tank and a regulator. In any case, why do you say/think you can't use "compressed air"? Are there other requirements for this air that you haven't mentioned yet? Temperature? Dew point?
    Last edited: Nov 5, 2015
  5. Nov 5, 2015 #4
    Henryk - I have been considering a lateral piston pump. I think that will be the quietest, lowest maintenance, and cleanest option. Diaphragms seem to wear out too quickly and the diaphragm material can be an issue. As for the opening, it is a pre-developed heat torch, so I am limited to their current design. Eventually, I will have a custom design created, but currently I am limited to what is available on the market. The larger the air torch, the larger the needed airflow is, so going larger doesn't help much.

    russ_watters - I have a clean air application, so no oil, rubber, or leachable materials. The air doesn't have to be sterile, but it has to be clean enough to breath, so to say. There is no other pre-pump issue (there will be high temps downstream, but not at pump intake). For compressed medical air, I am looking at either a huge operation (and cost) or a small, more portable tank/compressor. The large system could work, but again, >$10,000 for the initial setup and that only gets me an air supply. The other thing is that this will be in an unsecure area, so I am a little concerned about possible injuries as this is not an industrial application (not trained operators). Honestly, I would prefer compressed air in the long run because it would scale better with growth, but cost and safety are limiting it as an option for the startup.

    Finally, so if I am reading this correctly, the biggest issue to overcome is the 8.3 psig pressure drop. If I can find a pump/compressor that can generate a high enough flow at that pressure rating, I should be fine.... correct?
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