Small Fan with Flap?

[JavaBen]

As part of the project that I'm building - a BBQ Smoker Combustion Chamber Controller - I need to be able to turn on and off a small fan that pushes air into the combustion chamber - around two (2) inches in diameter. This has been built, and works great - some fine NC style BBQ is being produced - using an expensive valve I found....which is too expensive to use for a backyard cooker.<p>The problem is that when the fan is off, too much air leaks into the combustion chamber, causing it to run too hot (this is on a Big Green Egg, which is very efficient). <p>I'm looking for something like a fan that has a hinged flap that would close, cutting off the leaking air that's going through the fan. I've looked everywhere, but there doesn't seem to be anything like this commercially available.<p>I've found solenoids, but they typically have too small an opening, as they are expecting higher pressures - I'm working with very low pressures here.<p>Other solutions I've found are way too expensive - $60 or more. I need something around $10 or so.<p>It would seem that a small plastic butterfly valve (motor operated, or solenoid operated) would be good, but again, I can't find them at an affordable price.<p>Any solutions or ideas?<p>Thanks,<p>Ben

[myp71]

Bathroom fans have a flap on them.Plastic and Cheap for the whole fan .<p>
Just a thought

[jwax]

How about the air regulator flapper in your cars' intake pipe? A very light spring would keep it closed when the fan is off.
So, is this a smoker, or a BBQ? Got a webpage?
John

[cato]

Up here, where it gets d%mn cold in the winter, we install diverters in the clothes dryer vent tubing. In the summer we set the flap so the warm moist air flows straight through and out of the house. In the winter we set it so the warm moist air vents into the house.... sort of a poor mans hunmidifier....<p>The diverter is in your $10 price range, and thats retail, at SEARS HARDWARE. 'course they are manually operated....but maybe you could rig something up.

[upsmaster]

How about the type of exhaust cap found on large trucks. Metal counter weighted flap valves good model to start with maybe.
joe

[JavaBen]

Hey! Thanks for all the ideas! Some comments:<p>Re the Bathroom fan: good idea, but it's too large. The amount of air required to lift the fan would turn the smoker into a blast furnas! <p>Re air regulator flapper: Have tried to locate different dashboard components in the past, but found them all to be too expensive - way past the $10 or so price I'm looking for. Maybe I'm looking at the wrong parts??? Also, I've got to be able to open an close the flapper via electronic controls. Also, this is a smoker for cooking BBQ! BBQ is a noun - it's the end product - the stuff you eat! So, there's smokers, and there's grills.....and if you're lucky, you can find some BBQ that was smoked on a smoker! Re Web page -no, not that's available at this time. Feel free to email me with any questions though - I've been learning how to make BBQ now for 18 years!<p>Re cloths dryer vent diverter: Have looked at those at Home Depot, but same interface problem - rigging up 'something' to open and close it and still remain within the $10 hasn't been a success!<p>Re Exhaust cap flap: Good idea, may be able to counterbalance it enough for a small fan to lift! Are you aware of any around 2", for around $10?

[Ron H]

Have you tried searching for "electric damper"? You would have to use a separate fan.<p>[ June 06, 2004: Message edited by: RonH ]</p>

[MrAl]

Hello there,<p>cato:
Hope you dont have a gas dryer, because they
output gases into the atmosphere not good
for humans to breath in.
Electric might be ok as long as the filter
is clean.<p>Idea #1:
Another idea would be to simply install a
piece of light sheet metal that hangs due
to gravity on two needle bearings (actually
two pins or small nails). When the fan turns
on it can blow the sheet outwards a little
enough to allow air flow. When the fan turns
off the sheet rotates vertically again closing
the vent.
The sheet would have to be heavy enough to prevent
unwanted air flow when the fan is off but light
enough to allow air to pass when the fan turns
on. Plastic could be a problem if there is
heat build up in the vent pipe.<p>Pretty interesting would be a little servo that
opens the hanging flap <p>Idea #2 involves a kid's whiffle ball and
two diameters of pipe. The larger diameter
allows the ball to pass through it while the
smaller diameter doesnt.
The two pipes are connected together by inserting
the small pipe into the large pipe and gluing.
The ball is inserted into the large dia pipe
and the construction is turned vertically so that
the ball falls down through the large pipe and
bumps into the small diameter pipe and stops.
This action closes off the pipe from air flow.
The fan is installed at the mouth of the
small dia pipe so that when it turns on
the ball rises due to slight air pressure.
The light weight of the ball means it can rise
easy, but any back pressure keeps it against
the small dia pipe keeping the vent sealed.
This is the main idea behind a gravity operated
check valve, but even works ok when there is
some back pressure.<p>Take care,
Al

[perfectbite]

The counterweighted flapper valve:<p>If you are even the slightest bit handy take some non plated 18 ga. steel plate. Layout the shape you want and add two equal 3/4" wide strips maybe 5" long at each side at the top of the shape (you can always cut the excess off when it's finshed), tinsnip this whole thing out in one piece and using a vise or a vice grip hold the shape and bend those ears away from the plane of the flap and then slowly twist them through 90 degrees allowing about 1" for the twist. Drill holes in the 'new' flat of each ear each ear and insert a length of 1/4" gas pipe for the rocker bearing and put a piece of threaded steel rod through the pipe for a hinge pin. Drill holes for small copper pipe clips used as fastening brackets for the threaded rod (stand them off the burner's wall using the unplated nuts). Use doubled nuts for stops, DON'T use any plated metals on the flap steel, the threaded rod or the nuts or the counterweights. (Galvanized (Zinc) gasses off and plated nuts are tumbled in a poisonous Cadmium powder. If you make the 'ears long enough, twist them back into the same plane as the flap and bend them outward and drill holes in them too and use the holes for the threaded rod and nut counterweights and drive motor linkage. If it warps due to the heat, cut a blank of 1/4" steel and bolt it to the flap. Minimal design and effort, maximum effect and no brazing or welding. Maybe $10 worth of elbow grease. You should be able to get a HS shop teacher or student and have them make for you out of 1/4" steel plate in exchange for a sit down rib dinner for them and their wife or girlfriend or both.

[cato]

Are you sure you need a fan? Won't the chimney effect (hot air rising) draw more than enough air for a smoker? ...maybe then you would have enough in your budget for a damper control....maybe based on the motor and gearing out of a Crest SpinBrush.

[jollyrgr]

How about a METAL dryer vent in reverse?
Here is an example:
http://doitbest.com/shop/product.asp?ms ... 49Q8MGJ8LQ 4N5GP079EVTEBB6G4&mbrid=4724&dept%5Fid=1731&sku=275824<p>If you want something manual, how about using a duct work valve for regulating forced air HVAC systems? These come in various sizes and some have a handle to allow you to regulate the opening.

[JavaBen]

Hey - Great to have all the suggestions!<p>I just received a shipment of a car automatic electric door lock opener for $1.98 from a place in Tampa. Hope to get to try it out soon. It's the right price, appears to have enough 'umph' to open flappers. Not sure yet that it will stay in one position after a change, but hope to try it soon!<p>Here are some thoughts on the ideas above....<p>re: Searching for electric damper: Yes - have found some at around $60 - too expensive.<p>re: light sheet metal on bearings. The issue here is that either the fan would have to have too much pressure in order to to overcome the mass of the metal (thus overheating the coals), or if the metal were lighter, then it would be succeptable to chimney effect in light - moderate winds.<p>Re servo that opens the flap...have pulled a childs toy jeep apart to get a servo in the past to try out ... they were too weak to overcome a valve/flap heavy enough to not open on chimney effect. Heavier duty servos cost too much (more then the $10 I'm searching for).<p>re: wiffle ball. Didn't try this, but did try a diver's snorkle with ball-cage. Was too suceptable to chimney effect. Will have to think more about your idea....<p>re counterweighted flapper valve...will have to take a closer look at this one too.<p>re am I sure I need a fan. No, I know for sure that I actually don't need a fan; my current valve that I use uses the natural draft, but that valve cost $60. The problem here that I've encountered is getting a valve (or flapper, etc) to open at a low enough pressure at a cost that can be afforded. Will have to look at the Crest SpinBrush.<p>re metal dryer vent in reverse; same problem; while the vent will open on fan, it also will open on chimney effect.

[perfectbite]

You didn't mention if it is a continuing to the burner draft or an eventual from the burner draft. If it stops to reverse direction try an F 1.4/1.2 to F 16 iris from a junked lenseless SLR camera body. That iris may be strong enough to not allow a draft to develop, it may not be robust enough to stop even a gentle draft. <p>Don't bother taking the iris mechanism out of the camera. Take the camera back off, jam the shutter open, wrap the whole thing in cheese cloth, make a bracket mount for the camera body and use the Crest brush innards (Cato's idea) for the I/0 iris actuator (epoxy an eyelet or lever or even a gear ring to the F stop ring) and it may work for as long as it doesn't get gummed up. Who knows? Don't use your buddy's old Nikon though.

[JavaBen]

Man, you had me rolling in the floor with that one!<p>Thanks!