How does the venturi effect allow gas burners to operate without electricity?

[ameeno97]

Hi guys

I have a question regarding the working principle of gas burner. I was always have this question " How gas burner works using gas pressure lower -after been regulated- than atmospheric air ? "

Won't the the atmospheric air pressure prevent the gas from flowing?

Gas Burners

Both natural gas and propane burners work on the same principle called the "venturi effect". It says that as a gas or fluid passes through a pipe that narrows or widens, the velocity and pressure of the gas or fluid vary. As the pipe narrows, the gas flows more rapidly. What sounds like a surprise but holds true, is that when the fluid or gas flows faster through the narrow sections, the pressure actually decreases rather than increases. The venturi tube is a large diameter tube, gradually feeding into a smaller tube and then gradually becoming a larger tube

On the photos below there are examples of different burners, all operating on a venturi principle. One of the main advantages of Venturi systems is operation without electricity

The most important part of the burner is the orifice plug with the hole in it. This is the point where the gas escapes from the hose or a pipe and enters the mixing bell of the burner. Orifice plugs are replaceable and screwed into the orifice spud. Nearly all atmospheric (venturi) burners have a gas orifice that is accurately fixed in the burner throat providing air intake. The hole in the orifice is very small to provide the correct gas flow and to provide sufficient velocity to ensure there is a suction (vacuum) available for the correct air inspiration.
The question again is " When the gas start to flow from the regulator with say 2 PSI, Why the existing atmospheric air pressure (14.6 PSI) just prevent the gas from flowing?

I hope that you get my question right

 

[xxChrisxx]

Surely it's gauge pressure, the 2psi is 2 psi above atmospheric.

EDIT: Very nice first post by the way.

 

[Unrest]

Surely it's gauge pressure, the 2psi is 2 psi above atmospheric.

EDIT: Very nice first post by the way.

Haha nice indeed, now I know how the air gets in! But it's nice because it's lifted directly from a website.

 

[ameeno97]

Haha nice indeed, now I know how the air gets in! But it's nice because it's lifted directly from a website.

I have not claimed that I have written this by myself, I have just wanted to ask question and I wanted to make things clear so as to understand me well and if this will add a new info for others -Knowing how their gas burner works- I will be pleased.

 

[ameeno97]

Surely it's gauge pressure, the 2psi is 2 psi above atmospheric

I guess confusion came from that on some papers they use gauge pressure on sometime and absolute pressure on other times, they say:

The pressure after regulator is 2 PSI (gauge pressure), however when they want to talk about the atmospheric pressure they say it is 14.7 PSI

Very nice first post by the way

Thank you xxChrisxx but it is not my first post

 

[xxChrisxx]

I guess confusion came from that on some papers they use gauge pressure on sometime and absolute pressure on other times, they say:

The pressure after regulator is 2 PSI (gauge pressure), however when they want to talk about the atmospheric pressure they say it is 14.7 PSI

When talking about measurements it's common (and indeed common sense) to use gauge pressure, becuase that is what is easily measured.

I'd always assume that when a pressure is mentioned, it's gauge pressure. Unless it is obvious, or specifically highlighted, that it's absolute pressure.

Thank you xxChrisxx but it is not my first post

I know, the post count under your name gives that away. It's just a pretty well presented OP, and has pretty pictures to boot.

 

[Unrest]

I have not claimed that I have written this by myself, I have just wanted to ask question and I wanted to make things clear so as to understand me well and if this will add a new info for others -Knowing how their gas burner works- I will be pleased.

Yea I know. It's much easier to know what's going on!

But now my question is what stops the flame traveling back into the burner? I had assumed flames stay on the outside because there's no air inside. But it turns out there is.

 

[Nihilist]

Lower pressure and higher fluid velocity in the center of the flame encourages momentum away from the tube. I think.