Mailbox Mod Failure

[pinjim]

Hey all,
I built a mailbox mod and attached it to my Smoke Vault 24” rig. Unfortunately, it doesn’t work. The Smoke Vault isn’t drawing the smoke into the smoker. It seems like it’s the opposite, pushing the smoke back out the front of the mailbox, or just no movement at all. I had the top vent open on the Smoke Vault. I also put a lighter in front of the vent on the opposite side of the smoker and it seems like it’s blowing outwards too, not sucking in.

Frustrating since I have a good amount of time and money wrapped up in this. Any ideas?

 

[Smokey223]

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[chopsaw]

Just trying to look at the pics , I'm going to make a guess . Looks like the stock damper is still on the side of the box ? I would think that restricts the flow from the mail box .
You're trying to push a larger volume thru a smaller opening , and it's backing up on you .

Edit , Forgot to say you did some nice work on that . Looks great . You'll get it figured out .

 

[schlotz]

Yup, first photo. The restrictor is showing. Get that thing out of there.

 

[daveomak]

What's the size of the exhaust on the Smoke Vault ?? There should be about 2X the exhaust as there is for the inlet to the MB mod.... The openings on both ends of the flex duct should be 3" to fit the flex correctly... and provide adequate air flow....

 

[pinjim]

Everyone is correct, I did not remove what’s left of the restrictor plate on the smoker’s side duct. Honestly I didn’t want to as once I do that, it’s harder to reverse things.

The ports are 3” on the smoke vault. daveomak , are you saying I need a 6” exhaust on the top? I tried to close the mailbox vent so it’s restricted a lot more than the exhaust, no dice. If I open the door, smoke pours into the smoker. Close the door and it starts coming out the front of the mailbox. Frustrating!

I’m bummed as I was hoping this would just work. I may be back to wood chunks.

 

[schlotz]

Bottom line, you are going to need more airflow. Guess you'll have to decide on the restrictor plate.

 

[Winterrider]

Are you trying this without heat? If so try with heat and see if that aids in the draw. Lot of times when I cold smoke ( like today smoking cheese), I turn heat on about 70° for heat draw. Afterwards am able to turn heat source off.
If still doesn't work, try adding a stack.

 

[daveomak]

Everyone is correct, I did not remove what’s left of the restrictor plate on the smoker’s side duct. Honestly I didn’t want to as once I do that, it’s harder to reverse things.

The ports are 3” on the smoke vault. daveomak , are you saying I need a 6” exhaust on the top? I tried to close the mailbox vent so it’s restricted a lot more than the exhaust, no dice. If I open the door, smoke pours into the smoker. Close the door and it starts coming out the front of the mailbox. Frustrating!

I’m bummed as I was hoping this would just work. I may be back to wood chunks.

Cut out the restrictor plate.. You ain't ever going back once you get the MB mod up and running...
About the exhaust.... it needs to be about 2X more area than the holes you drill in the MB door.... As the air flows into the MB mod and smoker body, it heats up and expands... It needs room to exit the smoker body... If there isn't enough room to exit, the MB mod will be choked by the exhaust and won't flow air... and the pellets will not burn clean .....
Hope that makes sense.....

Dave

...

 

[pinjim]

Cut out the restrictor plate, no dice. Same result. I’m wondering if it’s just the nature of a propane smoker.

Like someone else observed, if I open the door, smoke immediately starts filling the chamber. Close the door and it stops.

I guess my option now is a small fan or just give up on the mailbox mod.

 

[schlotz]

Why not mod the door and add a hole? You could use tape or something to govern the amount of air being let in.

 

[daveomak]

The ports are 3” on the smoke vault. daveomak , are you saying I need a 6” exhaust on the top? I tried to close the mailbox vent so it’s restricted a lot more than the exhaust, no dice. If I open the door, smoke pours into the smoker. Close the door and it starts coming out the front of the mailbox. Frustrating!

I’m bummed as I was hoping this would just work. I may be back to wood chunks.

You are missing something.... Show a picture of the inside of the smoker......

 

[pinjim]

I don’t want to add a hole to the door. I think it’d diminish the ability to cook.

Here’s a pic of the inside. I partially wonder if the heat is hitting the chip tray and goes horizontal, “blowing” into the vent. My only issue with that theory is why does it matter if the door is open?

 

[daveomak]

The heat being generated by the flame is creating pressure by the gas and expanding air... Try a 90deg. elbow on the outlet of the MB mod..... That should work...
"Maybe" you will have to close off other inlets at the bottom of the smoke chamber.. but I doubt it... I would use a refer magnet and close only 1 hole at a time so you don't starve the burner for air... That could be dangerous... If the flame goes out, you will have a bomb waiting to explode....

Dryer Elbow

 

[daveomak]

Closing off 1/2 the burner gas holes, and adding a needle valve, after the regulator, will reduce the heat output of the burner... many folks have done that mod to their gassers... Makes for better heat control.... Make sure you have a low pressure regulator on the tank... MO-BETTA....


....

 

[suitcase]

I have never used a propane smoker but I will make some suggestions.

1. Close the vent on the other side of the smoker. Make all the air coming in go through the mailbox.

2. Put some legs on the Amazen so the air can get under it to improve combustion and it will stay hotter.

3. It appears that the inlet on the mailbox is about the same size as the outlet on the smoker. Open the outlet all the way and close the inlet about 1/3 to 1/2 way.

4. I believe the propane will have it's own inlet (adjustable?) for the combustion flame. Plus when the gas burns it will add a lot of gases and steam to the inside of the box. If anything you may need another exhaust vent but the exhaust stack already mentioned will also make it draw more air.

 

[daveomak]

I would NOT close down the exhaust... That will create pressure in the smoke chamber from the air expanding due to the heat from the burner... You want a free flow of air to burn up any creosote from any pellets, wood, chips, chunks or dust you are using as fuel......

 

[pinjim]

I’ve tried every combination possible for the various vents. I did find that opening the vent on the other side made the problem worse.

I have a needle valve, but I’ve been running the rig at 225 to 250. Any more restriction will drop my temps too low.

I think the 90 degree elbow is worth a shot. And if that doesn’t work, I may create a better (higher volume) chimney.

Possibly the gasser doesn’t work because there’s so much space for air to enter around the burner?

 

[chopsaw]

Dave has you going in the right direction . The pressure inside the smoker box needs to be less than the pressure inside the mailbox .
I'm assuming he suggested the elbow , to create more of a vertical rise from the mailbox into the smoker .
I believe the elbow and a no greater than 4 " exhaust stack will improve your flow .

Edit , 4 " in length on the exhaust .

 

[daveomak]

The space around the burner will cause problems for convected air flow.. Having the exhaust able to "suck" the air from the CC is the easy way to get good air flow... A small blower on the MB mod is another... I have 2 small blowers on my meat aging fridge... It's ~3 CFM... Your smoker is probably around 4 cu. ft. ... so it would do a little under 1 air change per minute.... That would be a good air flow to start with... I notice the fan is out of stock.. Look for one similar and maybe get a voltage controller to slow one down if you can't find one slow enough.....

FAN for smoker