needle valve flow rates

Freds Edge

Freds Edge

Well-Known Member
Does anyone running a blown forge have an idea of the flow rate for their needle valve , now I know it is related to pressure but its also related to the orifice size of the valve . I am having to open my needle all the way to achieve welding temp at 6 psi,
 
That's presumably 6 PSI upstream of the needle valve and with a blown burner?

What happens if you feed it 20 PSI upstream of the valve? That should get more flow through the fully-open needle valve let you adjust the gas flow downwards with the needle valve as intended.

It's worth mentioning that gas flow through a restriction does not change in direct proportion to the pressure, but to the square root of the pressure. Once the pressure difference across the restriction reaches "about" 30 PSI, the relationship between pressure and flow changes because the gas speed reaches the local speed of sound and flow becomes "choked".

Doubling the pressure will increase flow by 41% ( the square root of 2 is 1.41). To double the flow, you need 4 times the pressure.

If you have a Naturally-Aspirated burner, you can ditch the needle valve and use the regulator to control the gas pressure to the burner.
 
With my Ribbon Burner forge I forge weld at about 1# pressure and the needle valve no where near fully open and with no flux. You need to adjust the fuel/air just like you would an oxy/fuel torch. For forge welding you need adjust the burner to a fuel rich flame so that there is no unconsumed oxy in the chamber.
Check out the Build a Gas Forge and the Ribbon Burner attachments on the Forge Supplies page at

www.WayneCoeArtistBlacksmith.com.

Let me know if I can help you.
 
Tim has the right info - crank the pressure up some. All needle valves are NOT the same so it's hard to say what regulator pressure is required for welding heat. Not only the pipe size (1/4" NPT etc) of needle valve but the internals of valve. Also as the forge runs a while you'll find you can turn the pressure down a bit as the forge settles in with full heat making it burn with more efficiency.

I'll light my forge with perhaps 15# of regulator pressure, then drop pressure to 8 or 9# for a while. Then wind up forging with 4 or 5 lb pressure.
 
I agree with both Tim and Ken's assessments.
There are so many variables when dealing with a propane forge, and even changing weather conditions can sometimes "mess" with things. Even the fact that your new forge isn't "broken in" yet, is likely having an impact.

For the most part, I never let myself get worried about how high the PSI on my regulators has to be.....as long as I'm not maxing it out. It's more important to make the forge run correctly, and once it's broken in, then you can start tweaking around with things. 6 PSI is actually is pretty conservative considering the size of these forges.
I suspect, that after several sessions of use (meaning days of run time) , you will find your new forge will require a certain psi when starting/warming up, and will likely find yourself turning it down during use. Speaking of warming up..... my forge of this type generally takes around 2 hours or more to warm up, before I start using it.....it takes a long time, and a lot of generated heat from the burner to heat up that much thermal mass, but not so much once the temp overcomes the mass. I find I'm always turning the fuel feed down on mine after a few hours of it running.....just to keep it below 2400F.
 
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