Moving air inlets for UDS to under the Firebox?

[Andrew Leigh]

I am building my UDS from two Stainless Steel swimming pool filters, cost nothing so worth a shot. I should end up with volume of 40 gallons which is perfect for my purposes. It will end up about 6" higher which also suits me.

The part that will be used as the base has a very convenient (I hope) 2" hole right dead center. Given the shape of the bottom part of the drum I will need to make a stand to lift it off the ground by circa 4". This got me thinking, rather that the traditional 3 each 3/4" inlets coming in via the drum walls at the bottom I was wanting to machine a very simple manifold to attach to this 2" hole.

There will be a ash tray separating the air inlet and the firebox so the inlet will not become blocked. The ash tray will have a 1" perimeter gap, so in essence the air will enter through the center with all the controls that the traditional UDS's have. However the air will move evenly under and then around the ash tray, using the full periphery rather that three dedicated inlets. This will provide a more diffuse air flow which I am hoping will lead to a slower and more even burn.

Yes I know this is a total overkill but given the toughness of Stainless Steel I have no desire to drill anymore than necessary and therefore would prefer to use existing holes.

Can anyone think of a technical reason why I should abandon my plan. Here is the bottom drum showing the relative position of the ash tray, side clearance 1.25". Below that the manifold relative to the drum outline.

 

[daveomak]

The traditional design works VERY well... Your design "could" be a better mousetrap...
May I suggest you use 1/2" full flow ball valves on your 3/4" pipe.. You will have better low temp control over the 3/4" valves...

You could stub 3/4" street ells into the bottom, in place of the manifold...

 

[Andrew Leigh]

May I suggest you use 1/2" full flow ball valves on your 3/4" pipe.

Thanks for the response, I will follow your advice, especially given that my drum is smaller.

I have never used ball valves before so a simple question. Then surely I could use a 1/2" pipe with 1/2" ball valves? They will both have the same internal restrictive diameter?

Or is the argument that the thinner pipe presents more resistance and therefore less air flow to the 3/4" valve which is coarser in control. While the 3/4" pipe is less restrictive and will deliver the full volume of air to the 1/2" ball valve which has a finer control.

Regards

 

[daveomak]

While the 3/4" pipe is less restrictive and will deliver the full volume of air to the 1/2" ball valve which has a finer control.

That makes sense to me....

 

[MeatSkull]

I say get some electrical reduction washers and use a 3/4" ball valve. If that isn't enough you can drill some 1/4" holes on the side level with the heat source, amazing how much air will get pulled through them holes with internal heat. JMHO.