Batch box pulsating sound out of main air port? Help?

Check the link to the below video to see what I am talking about.  Not sure if I am filling the batch box too full or i need to enlarge my main air port.  It seems my fire wants more O2...  Any ideas rocketeers?  

If all your sizes are to spec check to see fuel is an inch away from sides and top of burn chamber, and secondary air supply is clear. it may be as simple as piece of wood falling across the port opening (and the sound may even be gone by now.

If you are just doing some test fires for the first time you may want to look more closely at your port size as well as your air supplies. are you using the p channel or walker design for secondary air

I usually try to keep at least an inch in front of the port open.  I am also using a p-channel made of galvanized water pipe(1.25 inch)... I have measured the interior diameter and calculated my circular area to determine that the channel may even be a little bigger than the spec, but not by much.  I have experimented with placing small round pebbles to narrow the air path slightly, but does not seem to affect the pulsations.

As far as wood placement, I will leave about an inch plus from the roof of the fire box.  I have not paid attention to the sides as far as leaving a gap at all.  As far as that particular thing is concerned how are you able to keep a side gap consistent when the wood is falling in compacting into a coal pile structure?   This is day 3 running the unit, so I am in the test phase essentially. I still need to add quite a bit more mass to the unit overall and everything.  

One thing i did try was cracking the door, and that did stop the pulsation.  When i closed it started up again, although it seemed to slow down later in the burn naturally.  So i guess i am worried about the peak time.  Could i be starving it a tad?  Seems to burn clean.  Although i think there is a good amount of steam coming off my mass i have added internally.  For i do see some whit puffs coming out the chimney...

I will do some re-measuring to see if i am off by a tad...

Sounds like cavitation caused by lack of airflow, especially as how it went away when you closed the door. Was there suction when you opened/closed it?

-CK

To me, you must have a restriction somewhere downwards from the batch box port, not air inlet. I can see the flames coming back out the primary air.

Try to load less little wood, more like 3 4 inches logs, or splits. If it carries on. Check your gaps and the transition  plenum area. Then the bench or bell etc.

https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

Chris Kott wrote:Sounds like cavitation caused by lack of airflow, especially as how it went away when you closed the door. Was there suction when you opened/closed it?

-CK

There was no lacking of draft or smoke back.  I only cracked the door a small bit till i noticed the pulse stopping, kept it open like that for 5 minutes, then closed it again.  So i assume a bit of suction yes... Although i could not tell by feeling the door as I opened it explicitly.

Satamax Antone wrote:To me, you must have a restriction somewhere downwards from the batch box port, not air inlet. I can see the flames coming back out the primary air.

Try to load less little wood, more like 3 4 inches logs, or splits. If it carries on. Check your gaps and the transition  plenum area. Then the bench or bell etc.

https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

My transistion from riser to bell, to small bell, to bench, and then out the chimney are all larger than the 6" spec till the cimney itself.  There is 8 inch from the bench to the actual chimney port, where it is then reduced to 6" finally right before exiting the building strait up about 20 feet.  Im really not sure it is possible in my design for restrictions along the whole way.  I have a lot of surface area internally.  Not too much i dont think.  I can see if i can get a few pics or diagrams drawn so you have a full vision of my build....

Also my wood source is all 1.25"x3" give or take a bit...

It's tough to say if your exhaust is constricted or not just by matching the riser size to exhaust manifold. I just read a fairly complicated formula and explanation that talked about stream flow or some such, that pretty much excluded portions of some manifolds from being active in free transmission of exhaust. The net takeaway was that under certain circumstance you might need a manifold with three times the area of the riser cross section.

I'm not saying that is what is happening, just saying that depending on the design, simply matching sq inches may not be enough to funnel the exhaust efficiently into the exhaust pipe..

That being said, since opening the door a bit stops the pulsations, I would look at possible obstructions of air flow first.  I believe I remember a video with Erica Weisner making the point that minimum 1 inch above and on the sides (and away from the port). Do you have the 45 degree slope at the bottom on both sides to funnel the coals down into a contained mass?

It seems my main air port is about one eith an inch too small on the width.  I will grind it out a tad and see if that helps.  There is a place to start at least.

bob day wrote:It's tough to say if your exhaust is constricted or not just by matching the riser size to exhaust manifold. I just read a fairly complicated formula and explanation that talked about stream flow or some such, that pretty much excluded portions of some manifolds from being active in free transmission of exhaust. The net takeaway was that under certain circumstance you might need a manifold with three times the area of the riser cross section.

I honestly dont think this would be my problem.  I would love to rule it out for sure.  Stating that i do beleive i understand what you are talking about...  I ran across some information/discussion regaurding a similar concept a few years back.  I have dont these cross sections calculations on a previous unit.  My numbers then were safe as can be.  This one i have not gone through all those same calculations, but I feel pretty confident about these ideas to some degree.  I think mostly i have over compensated at all the points i could when sizing everything.  The idea was to also negate flue ash collection issues that would narrow gaps that restrict flow until i clean the unit.  Id rather not worry for the year so i had this in mind when designing my mass heater v2.0 this time.

For instance how i applied this idea...  internally i have square/rectangular ports into each successive chamber.  Gas movement will travel the fastest and most free in a smooth circular or tubular style fashion.  So seeing as i have about double or more than the size of the system(pi*r^2) at each port i guess im not worried here.   Keep in mind i would meaure areas of the square/rectangular ports as if they where circles in order to get the closest to what the actual free gas movement would be in real time.  This is to try to come up with a number that does not include areas where free gas flow is not active as much.  Obviously we can only get so close on the exact numbers when doing this.  I will include some pics of my whole system path to see if you can agree.  Again, I would love to rule out any issues down the line so to speak.  

The bigger bricks(the "T" shaped riser "cover" and "1st chamber", and the 20x24x72 bell)are all about 1.25inches thick., and the smaller bricks(12x12x72 bell) are about 0.5inch+.  I have 2 inch wool insulation on all sides of the "1st chamber".  The rest is open internally to the size of the clay flue bricks.  Also, these pictures start from the front and progess as i walk counter clockwise around the unit till i reach the final exhaust area.  Keep in mind there is a lot of mass to be added yet, so it is just the bare bone at the moment.  I hope this might narrow the troubleshooting for you helpful humans.  Thanks to all by the way...

Matthew, if opening the door a smidge, solves the problem, then it is the door the restriction. This is weird to me. The rest seems all right. From what you say. The second bell, being like a downdraft channel, this could cause restrictions too.

To explain,

Gases entering a small bell at the top are forced to go down against the stack effect. The gases make a stream downwards, at the path of least resistance, against hot gases raising close to the walls.  Gases close to the walls go up, the ones in the middle go down to a certain point, there's plenty of friction in such a system. Then the hot gases coming from the heat riser's bell, from atop; kind of stall, from their previous velocity. And come back up against the walls, being replaced by the cooler gases, which are dropping down.

It's a big mess in there.

It would have been better to connect the two bells at the bottom. Or make a single big one. Peter says, minimum  4 times the CSA in section for a bell. I have experimented, on small systems, with a small bell. And i didn't like it at all. And these were intake and outlet at floor level.

Well, enough babble from me.

I'm guessing you are counting on the natural cooling of the gasses to provide the movement in that second downward "bell" and doubtless you have your reasons why you didn't build one large bell to allow for a freer stratification, rather than keeping all those little exhaust molecules lock step marching along whether they want to or not.

It does look like the exhaust openings are large enough so let us know how it works out after everything dries out and you solve your air intake.

I fully understamd you both(satamax and bob).  I will go though this with you more to see if we can find a weak point in my design.  Here is a rough diagram of my ports sizes from the burn chamber to the 1st bell, 2nd bell, then to bench.  A little note.. the "fin" you see in there is basically an ash deflector sheild made of some old metal roofing so that flue ash is encouraged to fall to the bottom of the big(1st) bell where is has a 2 foot deep ash collection bin.  

So internally it goes from the riser to an approximate 15x13x13(L,W,H - in inches) cube that ports directly into the 1st bell.  Which is a sort of balloon shape chamber... 17x20x24 imternally at the top two sections,  it reduces evenly down to 17x10 the next two feet down where it can now get under that "fin".  It then ports out using a 12x12 hole to the 2nd bell(12x12x72 internally).  From there it goes into the transition to the bench through an 8x8 port.  The internal of bench as a whole from there never goes under 12x12 until the final exit port(8" black metal chimney pipe).  Where only then it is finally reduced from 8" to the 6" chimney port.  My chimney itself is a 7" stainless liner inside brick and mortar, and travels about 20 feet out the top center of my home.

Hope this also helps rule out what we have been talking about, but now laying it all out i can see my 8x8 port is most definetly keeping the hot air stratified in the bells maybe too well.  It does seem i could use more heat in the bench since it is very tolerable and i planed on adding about 1k lbs or more to the mass there yet.  

I will adjust my air port on the door to see if that helps the pulsations.  I also think i want more heat in the bench mass.  I will have to think about that one for a bit... I will get back with what happens when i grind out another 1/8 inch of the main air port width.  

Chris Kott wrote:Sounds like cavitation caused by lack of airflow, especially as how it went away when you closed the door. Was there suction when you opened/closed it?

-CK

By "cavitation"  do you mean how it seems to be consuming the hot O2 right outside the air port?  I am leaning toward this being my main issue.  

Although i think i am discoverying where i will make my first adjustment down the line to even out my stratification more throughout the whole system.  Thanks again all!...

bob day wrote:
I'm guessing you are counting on the natural cooling of the gasses to provide the movement in that second downward "bell" and doubtless you have your reasons why you didn't build one large bell to allow for a freer stratification, rather than keeping all those little exhaust molecules lock step marching along whether they want to or not.

It does look like the exhaust openings are large enough so let us know how it works out after everything dries out and you solve your air intake.

I would have made one large bell, but the bricks i had would have made it a lot more cutting to do so.

I think the thing is that right now your only "complaints" are the pulsations and lack of heat to the bench.

It may be a little early to worry about whether you are getting enough heat just yet since so much of that construction is wet, and the pulsations are likely going to be solved soon. Also, test fire batches are not the same as operating batches and once everything is warm and dry you will have a whole different animal, so it may be that two or three successive batches make everything work just fine.

I might hold off on adding that extra mass for a bit just in case  (I hope this isn't in the middle of your living room with your wife asking when will it be finished?  


I personally want to rebuild completely without a bench, one big bell and out. but then my area is pretty cramped and a smaller footprint would be better then stretching out a bench that I never use

bob day wrote:I think the thing is that right now your only "complaints" are the pulsations and lack of heat to the bench.

There is one more complaint while on that topic quick.  More of a slight concern maybe... the cracks you can see in the large bell were caused by the first couple test fires.  Those three sections have got up to about 350 degrees F external temp.  By this point they have stopped cracking btw.  As far a the rest it seems to stay under 220 F even after a third burn in a row, and the bench only gets to about 130 F so far.  

My concern with this is how to adjust things to keep it safe and have long life?  I thought of needing to add ceramic wool on the interior or exterior of those sections or just add a bunch of mass to the outside.  The theory behind simply and only adding more mass would be that the addition would protect the clay liners.  It would help keep the temperature from having such a large contrast from internal to the external surface of the liner...  by the fact that mass heatsinks heat into itself and spreads it relatively evenly.  For instance my home's air temps will always be much lower than the hundreds of degrees the hot gasses hold internally.  I understand that the reason there is cracking is this difference.  My thoughts were more mass would keep the increase and decreasing temps more gradual from interior to exterior if I am making any sense?  Thoughts on that too?

bob day wrote:
I hope this isn't in the middle of your living room with your wife asking when will it be finished?  

Oh it is, lol!  And yes, she has been asking too, heh.😉

ah the joys of married life.

The thermal wool will reduce cooling, and lessen the push of the exhaust out of the bell, adding mass could have its own set of challenges.

I think that's what was meant by bigger bells are just less trouble. cutting bricks may be a hassle, but it might save a lot of trouble trying to "tune" it in the long run, I just don't have enough experience to know for sure--it would likely increase temps available to the bench and maintain a stronger exhaust pressure without as much friction to have a bigger bell.


Can you increase the bell size and keep benches where they are?

So to update... sorry for the delay in getting some words out.   I ended up wideneing the hole a tad by removing the part of the lower hinge metal that was slightly covering the bottom part of the main port.  It has seemed to slow the pulsations quite a bit.  Secondly it has also seemed to keep the fire from "licking" out the port in this first test burn anyway.  I will test another one in a few hours.  Also a LOT of moisure has been evaporated finally, but still another day or so(or a few burns) I think to get to the dry state i am seeking.  I noticed improvement mostly at my final sysyem exit temps that have finally reach about 140F!  So impovement, but i feel i need some more adjustments.  When i feel it is dry as can be i will then, and only then start to add more mass...

bob day wrote:
The thermal wool will reduce cooling, and lessen the push of the exhaust out of the bell, adding mass could have its own set of challenges.

Ok, on to the topic of mass... i was hoping for some elaboration on what is meant here... and if there are concerns with my plans or things i should know before solidifying my system so to speak.   Basically i was hoping to add about two thousand pounds to the current build with rock, brick, mortar, and possibly plaster or hand made tile in the end to face it..  I guess my question here would be...  what kinds of challenges are there(or what are you refering to exactly)?  It seems reducing cooling may not exactly be the goal in mind.  So by default adding mass must be my best option...  since this will spread the heat out as opposed to insulating and loosing a cooling surface.  l think i get that part anyway.
If I am thinking correctly the added mass may keep the heatup and cool down more gradual.  Thus keeps the bricl from splitting more.

My goal also is to get the top of the main "big" bell's surface temp of up to about 400 to be batteried into mass instead of the air in my house.  Also i was hoping to seal the fault lines that were created during expansion from the internal/external heat differential of the large clay flue bricks.  Any issues percieved here?  Im not sure how else to takle the concept while probelm solving.  Any critism or encouragement here?

Sounds like you are working through your challenges, I have a whole set of challenges of my own, mostly brought about by too much uninsulated mass and wet conditions in the fire box.

I got one successful burn lining the batch with firebrick, but then decided to go with a cast perlite clay mixture, but just can't get it to do anything but smoke--I also added a big piece of soapstone on top --where I previously had firebricks cante levered to cover the top, and it's just losing way too much heat before it even gets started, my house is a smokey mess.

The point is, how important moisture can be in throwing off everything, I still am not sure exactly what I will do, maybe just drying out the cast sides of the firebox and insulating the top will be enough. I have five feet x1" x24" of ceramic fiber coming Thursday to redo the heat riser, some of that may become the top to the batch box--or I may just rebuild the benches into a major bell or...

Depends on how cold it gets, how fast--and how much energy I have come Thursday.

I'm also investigating the possibility of using regular fiberglass insulation--it is good up to 1000 degrees--almost the same heat resistance as mineral wool, and 20 times cheaper. I almost am tempted to line a riser with it just to see what it does--ie how it melts. Maybe it will form a molten sleeve surrounded by unmelted fiberglass, then I could line that with 1/2inch of ceramic fiber to keep it from melting further and it would be self supporting;-)

Just some stray thoughts, what will likely happen is I'll figure out how to get this batch box dry and  working and wait for the next warm spell to remodel, it already performed well enough on the one test to keep me going for at least another few months

Extra mass starts to insulate itself more, so you would really need to be adding internal surface area to accept the extra heat charge along with the extra mass.  I wasn't exactly clear on where you were adding mass, and how much was already there, but the real test will be once things are dried out and you are running your burns and seeing how it behaves. If it starts to smoke back or the exhaust is getting too hot or whatever then you will have to make adjustments.  There is also a limiting factor of system size as to how much heat you can expect to store.

Just to be clear however, I'm a newbie to these manipulations, and right now I'm just getting acquainted with some of the issues of batch burners. So I am likely not the best reference.

bob day wrote:
Just to be clear however, I'm a newbie to these manipulations, and right now I'm just getting acquainted with some of the issues of batch burners. So I am likely not the best reference.

No worries bob.  I appreciate the discussion at its heart.   Honestly a lot of the topics you have brought up I have read about and discussed fairly thoroughly in the past with satamax, peter berg himself, allen lumney, erica wisner, and others.  As I stated earlier I have done a lot of these internal surface area calculations and such for a previous system so I feel I have a pretty good grip on the conceptual part of what that data can bring me.  Since I moved into the old farmhouse last year i have a whole new set of variables.  This time around i am also doing a batch box instead of a j-tube, and incorporating a bench into the design too.  It has been a while since i have asked myself questions regarding the topics you brought up.  It has been a great refresher of sorts, and has me confident i can do these troubleshooting tasks.  Thanks again everyone!

As for smokeback...  i have none. I have excellent draft through my chimney.  So for the most part it does seem the system is opperating correctly.  I do have a slight smell of wet campfire, but this is mostly the wet beachrock i added around the core for mass.  Which is made up firebrick for the box, and a cast of kastolite li30 for the the riser if you are curious.  

For the rest of the system i have "no mass", just clay flue tile that ranges feom.about 1.5 inches thick to about .6 inches.  I hope to add at least 2k lbs to it.  Currently the mass keeps the house warm flor about 14 plus hours pretty easily, and even then the firebox seems to have heat in it still.

Check my video below.  I finally did another good burn session.  The main big bell got to about 420 F shortly after the video.  The exhaust got to about 140 F.  So yea its still pulsates.  The bench is still a lot colder than the rest of the system.  It was interesting i caught the draft affecting the cracked mortar near the big bell fault line.  I should seal that it seam it seems.  i have not seen smoke come out at all so this is why i have not done that already..  anyway my port widening didnt seem to do the trick as i though.  Do i need more air still.. is that even possible?  Too many bells and not enough free gas movement?  Too much internal surface area possible?  
What do you gurus think?

P.S.  Anybody have the formula handy for calculating what my max internal suface are should not exceed.  Im trying to rule out all potential issues.  

P.S.S. In the chimney I have about 16 feet or so of space under where my exhaust port plugs in that goes dow to the old basment cleanout door.  I once was told that extra unused space could affect how the draft has power.  Could this be or aid to the cause of the pulsing maybe?  Just figured id mention my other thoughts too...

https://m.youtube.com/watch?v=u8d4oAhLPzI

http://donkey32.proboards.com/thread/1822/sizes-single-bell-systems

Does the pulsation still stop when you crack the door? Since that was one of the first things we talked about and you said you were widening the air inlet I'm guessing you haven't been able to find a sweet spot managing just the air inlet alone.

I'm going to give a guess that the pulsations are caused by the relatively small chamber above the riser and the immediate redirection of the very hot gasses downward. (did someone say that already?  it sort of reminds me of my ram pump on steroids.

In your system the riser gasses traveling at a high velocity suddenly hit the top of the first "bell" and bounce around a bit, not like a convection current, but more like a fire hose. most of that stream is forced down the second pipe, but I can see where there could also be a fairly strong back pressure created temporarily that starts to push back against the hose stream.

When I think about it as if it was a fire hose and then try and figure out where that resonance is occurring, my mind gets lost in the possibilities. But with all those possibilities the solution remains the same, bigger first bell.

It directly relates to what has been said about the larger bell sizes being less fussy.   In a larger bell above the riser that fast stream from the riser hits the roof but then can spread out in all directions, losing speed as it collides with the other molecules in the chamber.

This has been quite interesting to me since I started thinking about an obvious fact that the high speed at the end of the riser ultimately turns into a much slower speed coming out the exhaust,  So the overall system is actually expanding and contracting the air volume inside it, although it is all being done on a molecular level as gas volume increases and decreases due to temperature exchange.

Then that thought leads into why doesn't that expansion and contraction manifest more noticeably in more of our designs and I guess the answer to that is volume. a pneumatic shock absorber if you will. the larger internal volume of the gasses allows for a more gradual loss of temperature/speed.  The most noticeable temperature differential starts at the top of the riser and that is where those gas molecules need to be able to give up their high speed to surrounding gas molecules that have already given up their speed to the walls of the bell.

It might be possible (as in your case) to keep those molecules moving extremely fast for longer periods by restricting bell size, but the flow dynamics are far different for a meandering stream than for a firehose.  So all rules about transitions and bell shapes would need to be adapted.

It occurred to me that the solution might be to shape that top bell a bit differently, eliminate all dead end corners and make a smoother transition to the downward bell.

If all I had to do was play with fire, it's something I'd be tempted to try. There would be no guarantees just fun along the way watching the different behaviors of the monster along the way.

Of course with winter coming on and a disorderly living room, just cutting the bricks and building a bigger bell might be the safest way out.

I will respond more after this next burn.  For now here is another pic...

Myself, i would enlarge the 8x8 next to the cleanout. And remove that fin thing.

During the burn i opened the door a crack and caught another wiggle.  There is no super audible pulsation at this time...

https://m.youtube.com/watch?v=h13AODK_yRI

This is before i opened the door a crack about 10 minutes or so into the burn.  

https://m.youtube.com/watch?v=JnYoHtXAG0U

This is about 5 or so minutes after i open the door a crack....

https://m.youtube.com/watch?v=47B7yWw5g9w

Have you noticed that smoke before, or is this the first time you looked at it?

Could that still be from drying the thing out?

taking a longer time to warm up?

what do you think about what's happening?

My running synapsis... it seem there is likely a form of turbulance in my sysyem somewhere.  I will have to think hard on to where and how to go about enlarging my first bell area practically.  I need to be precise this time through if i am to dismantle.  For me winter is here about a month ago, lol...  This door "wiggle" i found seems to point to something further down the line causing the pulsations.  I am not sure what else to suspect based on what has been discussed.

As for the air intake concern it does seem i could get away with enlargening the main port more possibly.  I do seem to be getting a clean burn when there is more air than just the main port, or at least this test burn is shows this.  I will have to test another batch later tonight after i get it cooled a tad to see if starting out with the door cracked keeps a good burn going earlier in the batch.  Because for now i have only done so many tests.  I also will have to run a burn with the door closed again to test my efficiency visually from my chimney output for comparisons.  

bob day wrote:Have you noticed that smoke before, or is this the first time you looked at it?

Could that still be from drying the thing out?

taking a longer time to warm up?

what do you think about what's happening?

I have been watching, but until today i have not been taking it too seriously because i know of the steam from drying out was a factor.  At this point though i am getting a clean burn at some point in the batches so i assume we are getting pretty dang dry.  More batches are needed to test no doubt.

Satamax Antone wrote:Myself, i would enlarge the 8x8 next to the cleanout. And remove that fin thing.

I have been seriously considering both these things.  For i know the pull of the system should no doubt be able to wiggle that flimsy sheet metal roofing peice i used for the "fin".  Plus it does reduce the 1st bell in an odd spot... as it seem the gas flow would be trying to rip under the flap likely pushing on it a bit so that the gas could get to that next port to the bench.  My visual in my head is a wing trying to sustain integrity with jet stream whipping over, under, then up the blade.  I would just imagine there could be a "wiggle" from that pretty easily. Seems logical and most definitely possible anyway.

Also the 8x8 is just my smallest port.  No doubt a reasonable culprit.  Also these two things may be the easiest and fast fixes.  So eliminating them sounds like a good strategy.  

It sounds like some kind of internal turbulence creating a choke point. If I am understanding it right, its like the back end of the system is working so well when it gets heated up that it's creating vacuum inside because it is trying to draw more than the intake will allow. The vacuum pulls as long as it lasts, then it breaks as the vacuum gains purchase on the incoming air mass, which is then strangled into vacuum as the system tries to pull all that air out of the system, hence that pulsation, or cavitation. The vacuum pockets are like air bubbles forming in the motion of a propeller underwater.

I think you need to be able to vary the amount of air going in better than you can now. The fact that cracking the door a bit helps just proves this, I think.

-CK

Chris Kott wrote:It sounds like some kind of internal turbulence creating a choke point. If I am understanding it right, its like the back end of the system is working so well when it gets heated up that it's creating vacuum inside because it is trying to draw more than the intake will allow. The vacuum pulls as long as it lasts, then it breaks as the vacuum gains purchase on the incoming air mass, which is then strangled into vacuum as the system tries to pull all that air out of the system, hence that pulsation, or cavitation. The vacuum pockets are like air bubbles forming in the motion of a propeller underwater.

-CK

You seem to have a much better grasp on these concepts than I.  Your propeller example sort of parallels my aerodynamics thought a bit... what is your take on that "fin" i have.  Would you think it could aid in creating this mini vacuum effect.  My idea was that if the push and pull of the gasses "wiggled" that fin it could cause a sucking and pushing as it wiggled up and down(if it is for sure.  Cant see in there to verify obviously)  I just am curious if my spacial visuals, and the concepts you are being drawn to bringing up to me allign at all?

Chris Kott wrote:

I think you need to be able to vary the amount of air going in better than you can now. The fact that cracking the door a bit helps just proves this, I think.

-CK

Keep in mind the door "wiggle" points to that air restrictions are likely not the only possible issue or contributing factor.  I opened the door a pretty large gap(much larger than spec would ever call for air supply demands), and still a wiggle.