# Flow in small pipes

Is it possible to have a flow rate of 10lit/sec for air in a pipe of diameter 6.35mm (1/4") at a pressure of 1 bar?
As in this case, the velocity of air nearly equals the velocity of sound.

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it needs a pressure of about 1,6 bar

how did you come up with that value (1.6 bar), if you are saying pressure between 1 to 6 bar will it work at pressure of 1.1 bar?

For me it is necessary a pressure of 1.6 bar to create a flow velocity of 10 l/s, that is 1.0 bar is not enough.
If you really want I may try to propose a possible reason of it.

according to you, 1.6 bar is wrong? let me know.

I am not getting it, how exactly 1.6 bar

I'm not so sure; i've only tried to resolve the problem because it seem interesting to me...

Simplify the navier stokes equation so you have a 1D velocity profile. If you leave in the pressure term you can compute the pressure gradient knowing your desired flow speed. Your pipe is small enough where it will be laminar.

First, do you mean 1 barg or 1 bar (as in, atmospheric)?
Second, do you mean 10 L/s at standard conditions (i.e. NL/s), or 10 L/s "actual" air flow (as in 10 L/s of pressurized air)
Third, when you say the pipe is 6.35 mm / .25 in, do you mean it's a 1/4" Sch. 40 pipe (that has an inside diameter of 9.2456 mm)?
Fourth, what's the length of pipe that the air will be travelling through?

Assuming your 10 L/s is FAD, or at normal conditions (not pressurized volume), That is .6 m3/min through a pipe with an ID of 9.2456 mm, which gives a normalized air velocity of ~149 m/s. That's less than half of the speed of sound, but it's still extremely high. Pressure losses for that air velocity are very high, which means that in order to sustain flow, the longer the pipe length, the higher the supply pressure will need to be. At 1 barg, you may be able to get that flow rate through a 2-3 meter long pipe, but you'll need significantly more pressure for longer lengths.

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billy_joule
First, do you mean 1 barg or 1 bar (as in, atmospheric)?
Second, do you mean 10 L/s at standard conditions (i.e. NL/s), or 10 L/s "actual" air flow (as in 10 L/s of pressurized air)
Third, when you say the pipe is 6.35 mm / .25 in, do you mean it's a 1/4" Sch. 40 pipe (that has an inside diameter of 9.2456 mm)?
Fourth, what's the length of pipe that the air will be travelling through?

Assuming your 10 L/s is FAD, or at normal conditions (not pressurized volume), That is .6 m3/min through a pipe with an ID of 9.2456 mm, which gives a normalized air velocity of ~149 m/s. That's less than half of the speed of sound, but it's still extremely high. Pressure losses for that air velocity are very high, which means that in order to sustain flow, the longer the pipe length, the higher the supply pressure will need to be. At 1 barg, you may be able to get that flow rate through a 2-3 meter long pipe, but you'll need significantly more pressure for longer lengths.

1> I mean atmospheric conditions
2>10L/s as in NL/s
3> Inside dia 6.35mm
4>length of pipe is 1.5 meter

My actual setup is such that I have a pressure regulator that will give outlet pressure of 1.2bar and have 1/4" port size (diameter). My requirement is to have 10L/s flow of air
at the outlet of pressure regulator. Manual for that pressure regulator shows following flow characteristics i.e. it can supply flow rate up to 600lit/min. But with these conditions velocity will be close to 300m/s. SO I am confused if this is possible in a practical situation. Pressure regulator specification inlet pressure 5bar outlet pressure 1 bar to 1.5 bar

Also many of pressure regulator companies show pressure regulator with port size of 1/4" and flow rate even up to 2000 Lit/min at a pressure of 2 bar, isn't this also a similar situation ?

Also I would like to know if similar conditions are possible with 1/2" port size pressure regulator ?

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