Roaster Troubleshooting

[CavalierCoffee]

I have a Primo roaster that has recently started to "backfire" on me. This has been and still is a great roaster. Recently, when the temp. reaches around 300, I get a backfire, (for a lack of a better term).
This is a small build up of unignited propane that causes a small boom sound when it ignites and a short flame to shoot out the back of the roaster where the gas nozzle is. It does it once or twice but stops as the temp. increases.
I'm not sure what the cause might be and was hoping to get some info. from someone who may have experienced a similar situation with their roaster.
I'm wondering how or why there would be a gas buildup in a hot chamber? Could this be an airflow issue within the roasting room? I'm at a loss as to how to remedy the situation.
Thanks in advance for any help with this you might send my way.
Scott

 

[JumpinJakJava]

Scott, do not know if this is your problem, but since you uses LP, found this online:
This phenomenon occurs mostly with LP gas and even has an industry name of
"extension pop". This pop is caused by the nature of the LP gas (but occasionally with
natural gas) which burns hotter than natural gas and runs at a higher pressure.
When the flame is on LP gas is being pushed into the burner at a certain pressure
and when it is turned off the pressure inside the burner is immediately reduced to
that of the surrounding atmosphere. Because of the high heat of propane it ignites
most of the gas inside the burner at once and causes a popping sound. The hotter
the burner and the bigger the burner the louder the pop. "

Although, you may like to keep an eye on that, or have it officially checked out by a licensed
LP technician. Safety first. Hope it helps.

 

[topher]

Be careful. One of my old employees had left the hopper lever open on top. He also had the airflow around 75% closed. gas leaked out of the roaster and into the cooling bin. Once the chaff collector filled with gas the after burner ignited it...booom. Nice hole in the bottom of the chaff collector. Knocked him across the room and we had a wee fire. I am not saying this is what is happening in your case...but to me it sounds like it could be an airflow issue. How long have you been using this and how long has this issue been happening? What is your maintenance schedule like and what do you do for it? I would scrape all motors and pipes..Where there are "elbows" make sure it is the original metal and not build of of creosote. If builds up it can look like it is actually the pipe but can really screw with your airflow... if it continues I would call a licensed LP tech.

 

[CavalierCoffee]

Thanks JumpinJakJava and Topher
I appreciate the feedback.
I haven't roasted much more than 150 pounds with this machine. I roast in 3 pound batches and I don't roast past full city plus. I clean the chaff from around the drum area after two, sometimes three batches and empty the collector after a half dozen or so.
I always close the hopper lever and open the air flow slot to about 3 inches at high heat to start and eventually close the air flow to 2 inches and turn the heat down to medium.
It starts to pop within a minute or two of doing this. It never used to pop. This started a couple of weeks ago. The room is colder with winter coming on, but other than that, I can't come up with any changes in procedure I might have made.
I have an email out to the Mfg. so hopefully I'll get some info. from there as well.
Scott