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About timgunn1962

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    Lancashire, England

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  1. You are right and I am wrong. Thanks for correcting me.
  2. The pressure in a Naturally Aspirated burner is needed to impart speed to the gas issuing from the jet. There is some quite complex, and not particularly intuitive, Physics going on, but basically there is a conservation of momentum thing happening which draws in air and mixes it with the gas. In a blown burner, the air is forced in, rather than being drawn in by the fast-moving gas stream, so there is no need to have high pressure and a high-speed gas stream. A bigger jet will give a lower speed for a given gas flow and the lower speed is obtained with a lower pressure. High speeds tend to be associated with laminar flow, while low speeds tend to be associated with turbulent flow. Turbulence is needed to mix the gas and air effectively, so lower gas speeds are preferable where high speed is not needed to get the air in the first place. Flow through a jet varies as the square root of the pressure: half the flow needs a quarter of the pressure. Double the flow needs 4 times the pressure. If you are going to use a “jet”, it and regulate the gas flow on pressure, the “jet” needs to be sized to give a useful range of flows across the pressure range you can set with your regulator. Finding an appropriate jet size for a NA burner is the difficult part. Not needing to do it for a blown burner is probably the main reason blown burners are usually considered easier to build. If you use a needle valve (which can be thought of as an adjustable-area “jet”) to control gas flow, you don’t need to worry about regulator pressure overmuch.
  3. 1mm gas jet on a blown burner seems very small. Are you getting any Dragons Breath? If not, You are probably running too lean and would benefit from a bigger gas “jet”. A small jet and high pressure are needed in NA burners because the gas velocity needs to be high to entrain air. Blown burners have the blower for the air and gas velocity is not needed.
  4. I had an IR thermometer, good to 1600 degC. Pretty close to useless for most smiths. It ended up with a guy who makes some nice kitchen knives. He uses it to check for consistent temperatures when taking billets from the forge as they come out. Once he’s got the first one or two working right, he doesn’t care what temperature value he is reading, just that the reading is the same each time. When the steel is in the forge, it scales to some extent. When it comes out into the air, it scales some more. When it gets hit, the scale gets knocked off and immediately starts reforming. The emissivity changes with every process and every second that passes. There is no one value that will give accurate temperature readings.
  5. I did a bit of playing with jet sizes and found the Butane jetting to work very well on Propane forges. I think the factory jetting is intended for “normal” heating applications which use both primary and secondary air. For Propane forges, there is usually no secondary air so the Propane jetting runs pretty rich and not quite hot enough for welding. The Butane jetting is smaller, so runs less rich and a bit hotter when burning Propane: certainly hot enough for welding bladesmithing steels, though I don’t know whether it will manage WI welding temperature. It’s still rich enough to limit scaling in the forge, so there’s some scope for reducing the jet size further to get even higher temperatures if needed. The Amal jets are available in closely-spaced increments and the sizing is pretty intuitive.
  6. Try increasing the size of the hoses. If you can double the diameter of the long section, the area will increase by a factor of 4 and the pressure loss will go down dramatically (the physics gets complicated, but a first approximation is that the pressure loss varies as the square of the velocity, so you'd get something of the order of one sixteenth of the pressure loss along the same length at the same flowrate). Shorten the hose and the pressure loss will vary with the length (as a first approximation). Ten feet of 1 1/2" hose will give "about" one fortieth of the pressure loss of your twenty-five feet of 3/4" hose. If you go for 1 1/2" hose upstream of the tee, get the tee as close as possible to the burners and use the 3/4" hose (that you already have) between the tee and the burners, things will probably get a lot more manageable.
  7. It sounds to me like you probably don't understand the physics well enough to be asking the right questions. The lines between blowers and pumps can be blurry at best.It's certainly not as simple as changing from one to the other at a defined pressure. "200-300 CFM" is a very wide range when considering the pressures needed to drive flow through a tube. I'd suggest an online search to find the catalog for "Rotron Regenerative Blowers" and read the technical stuff near the back. It'll either give you some answers or will give you a better idea of the appropriate questions. There is a "friction loss per foot of tubing" chart that should prove particularly instructive.
  8. Can you buy jets for the burner separately? If it needs secondary air as it stands, with the choke fully open, to get the maximum temperature that you need, fitting a smaller gas jet will increase the primary air:fuel ratio and reduce or eliminate the secondary air requirement. I would find out what jets are available, if any, and how fast you can get them, before butchering the burner mountings. That way you can see what you get and decide whether to try different jets or cut-and-shut if it does not do what you want.
  9. On the 3/4”, I think the threads in the body are 3/8” BSPT, which will be “about” the 15mm-ish you mention. Personally, I would use a 3/8”BSP hosetail with the barbed end sized to suit the hose. I use O-clips to secure the hose. If your configuration has the burner at top-centre, pointing downwards, there is likely to be some chimney effect and the heat transfer up the burner when it is shut down may make using hose unwise. Rigid metal tubing may be better.
  10. Stuff happens. I think we all knew what you meant. Occasionally making a mistake is normal: it certainly doesn't mean you should stop thinking. I only pointed it out because it's the internet and someone encountering this thread at some point in the future might otherwise pursue a path of extreme frustration.
  11. If 1:12 is the "fast" limit, it seems like longer tapers would be "slower", so you'd be looking at 1:13 and onward.
  12. "Very close" is perhaps a tad optimistic. The gas flow at any given pressure varies with area, which varies as the square of the diameter (assuming the geometry of the hole entrance and exit remains the same). .0485"/.043" is 1.128 times the diameter, giving 1.272 times the area. On those numbers, the burner would run 27% richer than it would with the #57 drill. I actually get 3/64 = .046875 .046875/.043 = 1.09 times the diameter, 1.188 times the area and about 19% richer than the #57 drill.
  13. Reinventing the wheel springs to mind. That sounds a lot like an Amal injector, but without the facility to vary the mixture at will.
  14. The real answer is "whatever works best for you". There are waaay too many variables for a single answer to cover all the possible scenarios. Even the color of the DB will vary in different ways with different setups: some will tend to richen up more than others once the openings become restricted.
  15. Turning the pressure up often works.