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Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/08/2017 1:48 PM

How do you calculate Air Flow Rate (CFM)

if you only Know pressure of supplied air and Hose Diameter?

Example:

If a compressor supplies air at 75 PSI through a 1/4" DIA hose that is open at the end

What is the air flow rate in CFM?

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#1

Re: Calculate Air Flow Rate knowing Suuplied pressure and Hose diameter

05/08/2017 2:23 PM

You have to know the length of the pipe...through an orifice would be ~80 cfm...

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#2
In reply to #1

Re: Calculate Air Flow Rate knowing Suuplied pressure and Hose diameter

05/08/2017 2:42 PM

Thank you for your reply ! ! ! The hose would be about 10 ft in Lenght.
What formula would you use? All the formulas that I have found include air velocity which I don't have

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#9
In reply to #2

Re: Calculate Air Flow Rate knowing Suuplied pressure and Hose diameter

05/09/2017 3:54 AM

The velocity cannot exceed the speed of sound at the given conditions of temperature and pressure at the hose outlet.

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#14
In reply to #9

Re: Calculate Air Flow Rate knowing Suuplied pressure and Hose diameter

05/09/2017 10:06 AM

True.

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#3

Re: Calculate Air Flow Rate knowing Suuplied pressure and Hose diameter

05/08/2017 2:58 PM

I have used Engineering Power Tools for approximating problems like this. quick and easy to make changes.

It also have flow rates in various orifice designs/sizes.

It has a version that you can try and if it looks like something that you could use, the end cost is nominal.

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#4
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Re: Calculate Air Flow Rate knowing Suuplied pressure and Hose diameter

05/08/2017 3:24 PM

Thank you ! ! !

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#5

Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/08/2017 4:25 PM

Take the cfm rating off the compressor nameplate, and use that for the first 5 mins. For the next 5 minutes, as the compressor overheats use a 70% rating off the nameplate, and for the next 5 minutes, call the fire department, because you may need them.

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#6

Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/08/2017 4:32 PM
Air Flow Pressure Results
Hose Diameter (in.):0.25
Hose Length (Feet):10
Gauge Pressure (psi.):75
Flow (SCFM):37.5
Pressure Loss (psi.)

74.50

Hose I.D. (in.)Total psi Loss (psi.)Hose Pressure Drop (psi/ft.)
0.1875338.053833.8054
0.2574.50467.4505
0.3758.84040.8840
0.51.94840.1948
0.6250.60290.0603

I quit at 37.5 scfm, since there was showing less than 0.5 psi residual pressure at hose end. You can try again (but 40 scfm is too high), until you show total psi loss of 75.0 psig.

gates air flow calculator

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#7

Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/08/2017 5:56 PM

What's the (atmospheric?) pressure at the outlet?...

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#8
In reply to #7

Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/08/2017 6:04 PM

Thank you ... Please Assume 1 ATM = 14.69 PSI (Absolute)

It's an air jet to clear debris from a section of a machine

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#11
In reply to #8

Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/09/2017 4:07 AM

If this is an actual application (and not homework) consider using an Exair nozzle it will reduce your air consumption and the noise dramatically.

Best regards,

John

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#12
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Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/09/2017 5:20 AM

Well, that's a change of plan, because now the hose isn't now open-ended; it has a nozzle on the end. The nozzle has a pressure/flow characteristic curve, which is available either in the sales selection literature, or with the information that came with it, or over the telephone with the nozzle manufacturer. All that is needed now is an actual pressure reading immediately upstream of the nozzle. So now it has stuff-all to do with the compressor.

Is there any point to all this?

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#16
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Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/11/2017 12:57 PM

Ahhhh, so the conduit is discharging into air, at essentially standard atmospheric conditions. Thank You...

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#13
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Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/09/2017 10:05 AM

It is zero gauge pressure, silly. It does not make any significant difference, more than about a 1%-2% correction even at near unbreathable altitude.

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#10

Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/09/2017 3:58 AM

The compressor won't be supplying <...air at 75psi...> if the hose is open at one end!

The flowrate will be the same as the maximum throughput of the compressor at the compressor outlet conditions (temperature, pressure), which will be found either in a performance curve in the manual that came with it or over the telephone in a call to the compressor manufacturer.

Air coming out of the free end of a hose isn't doing anything useful, though.

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#15

Re: Calculate Air Flow Rate Knowing Supplied Pressure and Hose Diameter

05/10/2017 5:54 AM

It might help to know the material the hose is made of. Different materials have different internal frictions. .....and is it flat round or corrugated?

....and the compressor max flow rate matters. Too much flow for a small compressor will cause the pressure output to drop - and hence the flow drops until an equilibrium is reached....

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