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Questions: Drilling out a burner orifice
Omega
I need more heat from a burner in a roaster I built, here > http://forum.home...post_52342

The orifice is so tiny, it's almost unbelievable. I found some orifice drills on ebay and purchased a #79, 77 and 70. The #79 is the smallest that I could find, it's .0145" in diameter. This will be somewhat of an adventure, since I have no idea what size of orifice I'm dealing with in the first place. Since I'm using 22 psi propane and just barely having enough heat to do a decent roast, I guess that enlarging the hole to at least a #79 shouldn't be too radical (I hope!).

When I pulled the jet out of the burner, I was surprised to see a sintered metal filter in the base, upstream of the orifice itself. What concerns me is drilling the jet and trapping shavings in the cavity formed by the drill and in the sintered material.

Any suggestions for doing this properly? Does anyone have input about the amount of heat that could be generated by an orifice of .0145"?

Thanks, Barry
 
Koffee Kosmo
The orifice size of the end burner won't give more heat
A change in orifice will change the flame pattern/type/shape

What will give more heat is a larger jet that supplies more gas volume
More gas = more heat

Cheers
KK
I home roast and I like it. Designer of the KKTO
Roaster Build information
https://forum.hom...ad_id=1142

https://docs.goog...lide=id.i0
Blog - http://koffeekosm...gspot.com/

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
 
allenb
Barry, the orifice supplying the venturi on my 1 lb gas fluidbed campstove burner was just slightly smaller than .0145" so the #79 should be fine. I ran the numbers through a BTU calculator and it will give you a max. output of 12,943 BTU's/hr at 22 psi. You should only need around 8500 BTU's/hr if roasting with a moderate spout height and not blasting more air volume than necessary. With the #79, you'll have some headroom which is necessary so you're not running with the needle valve maxed out.

As far as drill shavings getting into the filter, I think you should be fine even if they get stuck in it and will just become part of the filter. Give it a shot.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
allenb

Quote

Koffee Kosmo wrote:

The orifice size of the end burner won't give more heat
A change in orifice will change the flame pattern/type/shape

What will give more heat is a larger jet that supplies more gas volume
More gas = more heat

Cheers
KK


Hey KK, the burner he's using is one of those mushroom, multi-hole burners and he's not going to be messing with those but just enlarging the venturi orifice which you're referring to as a jet. This is the same thing as what we're calling an orifice. You're right though that if one alters the burner end-opening then you've re-designed the thing and will end up with a mess of a flame!

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Omega
Thanks for the btu calculation, allenb! I would like to get away from using 22 psi, since that's where the adjustable regulator maxes out. The #77 bit, that I also bought, would allow more flow, should I need more. Since the blower will easily loft over 2 pounds of beans, I might need some more heat if I want to do larger batches.

I appreciate all the input and help!

Barry
 
allenb
Something to remember when altering burners is you can end up with various issues with air/fuel mixture. After I increased the firing rate of one of my burners beyond it's stock configuration, the flame began to lift off of the burner and would easily go out. The increased gas flow through the venturi resulted in too much air draw. I had to block off some of the intake area of the venturi assembly to get the flame to drop back down to the burner plate. In the end, you should be able to adjust the intake area to fire nicely at very low firing as well as high fire but it may take some tweaking. Aluminum foil tape works great.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Omega

Quote

allenb wrote:

Something to remember when altering burners is you can end up with various issues with air/fuel mixture. After I increased the firing rate of one of my burners beyond it's stock configuration, the flame began to lift off of the burner and would easily go out. The increased gas flow through the venturi resulted in too much air draw. I had to block off some of the intake area of the venturi assembly to get the flame to drop back down to the burner plate. In the end, you should be able to adjust the intake area to fire nicely at very low firing as well as high fire but it may take some tweaking. Aluminum foil tape works great.

Allen


Good point, Allen. I've had some experience with propane ranges and have seen the difference that metering the air can make. I've given the concept some thought about the burner in the roaster, as well, but I'm glad you brought it up.

By the way, I had the first coffee from this roaster and must admit that it was much better than I thought it would be, considering that the beans were not especially good. Coincidentally, my daughter and her friend tried coffee from the third roast this morning over in Montana and they were very impressed. To say that this was very encouraging would be an understatement.

The drills for enlarging the jet should be here tomorrow and I might get the jet drilled, get the roaster back together and roast some beans this weekend, I hope.

I'll post with any additional developments.

Barry
 
Omega
I had the opportunity to drill out the jet in my roaster and reassemble it, and it worked out great. The roaster can operate at lower propane pressure and there is now enough heat capacity to easily speed up rate of rise at any point. The flame is very well formed and isn't blown out, even when using a huge amount of air flow.

Apparently allenb was correct in saying that the #77 drill was one size larger than the existing hole in the jet. When drilling, very little material was removed, but the increase in heat production is very substantial.

The one weak point of the roaster has now been completely eliminated and it's function is as good as I can imagine. It's great to have all the roast capacity and complete control over the process. I did two 14 ounce roasts and both turned out looking great; the roast times were exactly what I anticipated. I will attempt some larger roasts, looking to have one pound of roasted beans per batch. Since there's more than enough air flow to loft lots beans and plenty of heat available, I don't expect any issues.

The help on this forum is so appreciated!!

Barry
 
allenb

Quote

Barry stated: The help on this forum is so appreciated!!


Glad to help and really glad to hear your BTU's are now up there where you need them!

One thing nice about HRO is with our member lineup you'll always be able to get help in pretty much any area of roaster building and troubleshooting.

Keep us updated with your new build roasting adventures!

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
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