Hi all - first post and looking for advice. Bought a second hand forge complete with propane. Gets up to heat fine but sees to be backfiring. Adjusting the regulator makes no difference. Any suggestions?

"Huffing"?  Check that the orifice is pointing DIRECTLY down the center of the burner pipe!  I notice that they seem to have welded it in position so it can't be adjusted; a horrible practice if not ending up aligned perfectly! (Welding can shift things slightly...back when I had my first lesson the instructor had us weld a piece of 1/2" sq stock to a plate holding it in place with a finger on top so we could feel how welding one end shifted the other. )

It sounds more likely there is something in the gas assembly, which is working its way into the burners.

Sounds like pre-ignition to me.  Typically this is when the forge heats up and the flame front burns back towards the burner orifice faster than the air/gas mixture flows out of the mixing tube.  As others have mentioned I'm not a big fan of that version of the Riel ventauri burner.  The reducers used for the air induction seem too small and the gas pipe feed too large for efficient induction.  I would first attempt to adjust the air for more induction by opening the air gates at the back of the burner.  I suspect that any restriction at high fire will be a problem.

Good luck

Looks like the air choke on the back burner is completely closed.

Thanks all. Back burner isn't running (not needed for now). The tank came with the forge - I'm wondering if it's nearly empty. Winding up the regulator has no effect. 

As Latticino says, this is (often?) caused by the speed of the flame-front moving through the mixture faster than the mixture is moving in the opposite direction. It usually starts when the forge gets fairly hot because the flame speed increases as the temperature rises.

The flame will run back along the burner tube until it runs out of mixture (Propane will not burn unless it is mixed with air (or another Oxidising agent). The flame goes out. The gas keeps flowing, draws in air and mixes with it. The mixture reaches the hot forge and ignites. The process repeats.

Every time the flame-front moves along the burner tube, it heats it a bit, making the flame speed even faster.

If you can catch it quickly and turn up the pressure, you can often get the mixture speed faster than the flame speed and stop the problem. You have to be pretty quick to stay ahead of the burner tube heating up. You also need a big increase in pressure. The gas speed varies as the square root of the pressure, so doubling the pressure will only give a 41% increase in mixture speed. To double the mixture speed you need 4 times the pressure. 

Pussy-foot about giving it one or two extra PSI and you've got no chance.  

 

Post a pic of your regulator?

I can't really see it- but what's the pressure capability on it? It might be too low, or not properly adjustable?

Hmm... that should do it. Usually, its around 20-30 psi for a forge burner. At 5.4 bars- thats about 78psi according to google conversion.

Do you know how old it is? It may have gone bad, have another known good one to try swapping out?

I'm pretty sure that's a 0.5 bar to 4 bar regulator; about 8 to 60 PSI. There are lots of them on ebay in the UK and they are complete dog-toffee IMO/E. I had a couple of them, tried one, threw both away.

The 8 PSI minimum tends to make lighting the forge unnecessarily exciting and there's obviously no control at the lower end of what would normally be the working range.

The best regulators I have found tend to be plugged (no gauge) 0-4 bar Propane regulators from welding suppliers. These usually have a scale showing the (approximate) pressure setting on the side of the body, where the skirt of the adjusting knob indicates the setting. It's usually not much less accurate than a cheap gauge and is considerably more rugged than any gauge. The regulator is designed for industrial use and fine adjustment by less-than-delicate individuals wearing welding gloves. About twice the price of the 0.5-4 bar cheapies on ebay UK and, I feel, considerably better value.

Tim- ah! That would make a difference. I thought it was 0-5.4. Smh...

 

I'd wondered about that and had already ordered up a 0-2 Bar regulator (with gauge so I can see what's happening). Will that be sufficient?

2 bar, 30 PSI is usually fine. The square law for pressure vs flow through a jet in compressible fluids (gases) holds until the flow "chokes": the speed through the jet reaches the local speed of sound. This happens somewhere "around" 30 PSI for Propane. Going from 2 bar to 4 bar (30 PSI to 60 PSI) will therefore get you less than the 41% increase in gas flow that you'd expect to get if the flow didn't choke. There's no cost difference between a 0-2 bar and a 0-4 bar reg, and there's no noticeable difference in adjustability with the welding regs, so I tend to buy 4-bar for the "free" little extra at the top end.

A 4-bar reg is nice to have, but doesn't give you much over a 2-bar in the real world. I think you'll find the 0-2-bar will be fine.