Blast gate and manifold combination design

[mark a stephens]

Hey folks,


I'm setting up shop with an Oneida V3000 dust collector, ASTM 2729 6" pipe and fittings. My goal is to provide each machine with a full 6" pipe and divide that after the blast gate into some combination of hoses that total up to the 6"er area wise. There will probably be a lot of HVAC "hoods" and movable 2" hoses to make up for the feeble DC ports on most machines.


I started designing manifolds from PVC fittings with 6" to 4" wyes with 6" to 4" reducers... This manifold was larger than some of the machines! Due to the basement layout, DC ducting above and on floor, and 8', or less, ceilings, placement of this was awkward. Not to mention the expense of those wyes (there are plenty anyway coming off the ducts).


At the cost of some pressure drop, why not combine a blast gate with the manifold in a roughly 12" cubic box? The design includes auto turn ON of the DC. Since some of these boxes will be on the floor (e.g., table saw) behind the machine, I wanted the box to open with a rope and pulley system. The gate will hopefully close by gravity. DC turns off manually, not with gate closing. I plan on using 1/2" Melamine shelving for the gate, 1/2" MDF for the box with biscuit joinery and hardware sides for the gate stops. Plastic laminate (green in picture) provides slipperiness. A rubber flap seals the bottom but should allow for cleaning, but just in case, the front unbolts if the guide slots fill up with dust. (Extending the guide groves all the way to the bottom may alleviate this.)


Shown are two four inch and one 2 inch ports, but each machine will have tailored ports.


Comments are most welcome. Especially on:
- plastic film for spacing to make a gap for the gate seems hard to glue. This may not be a problem if I don't go the bolt route (no glue).
- the PVC connectors are couplers sawn in half, so I can use either pipes or flexible hoses (they "screw" in, a pin holds them). Better way to do this?
- Need a longer box => less turbulence?
- overkill?

thanks,


mark
227021227022

[Alan Schaffter]

A couple of comments-


Even with the laminate faces, whenever the blower is running and during much of the spin down, the slides will not likely close by gravity alone, unless sufficiently weighted. I make my gate faces and the slides with laminate. Before I added pneumatic actuation they wouldn't move easily when air was flowing.

I make my gates without spacers- when I assemble them, I put some tape on the slide to establish a very slight amount clearance, then join the gate halves together with laminate along the sides- fast, easy, and durable. I pull out the slide to remove the tape. If your slide and gate faces are flat you don't need a rubber seal, the gate will seal fine without it. There is a post about it here somewhere.

I would be a little concerned that dust might collect in the corners of your box.

The box will definitely reduce CFM and add to SP resistance, especially since the flow must make a right angle turn, so I wouldn't use too many of them. Frankly I would use one or two wyes after the blast gate instead of a box. If you are good you can make your own 6 X 6 X 6 wye by cutting an angled piece off the ends of two sections of pipe. Join them together at the cuts. A disc sander is helpful getting edges flat.

Air will want to flow along the path of least resistance, so don't expect much in the way of CFM or SP in the smallest pipe.

http://www.ncwoodworker.net/pp/data/1759/medium/Blast_Gate-exploded.jpg

http://www.ncwoodworker.net/pp/data/1759/medium/IMG_3019.jpg

http://www.ncwoodworker.net/pp/data/1759/medium/IMG_3140.jpg

[Michael W. Clark]

I wouldn't think you need a very tight tolerance between the gate and slot. The main thing is that the gate seals when it is closed. If there is some slop in the groove, the blade will be sucked back against the downstream side of the duct/housing and create a seal when it is closed. I would put the gate in the horizontal. Gravity can also act to close it at an unwanted time unless you get the friction fit exactly right. Let the blade go past the bottom of the duct or extend through the other side of the housing.

This will generate a significant amount of SP. Like Alan said, you probably will not get much flow in the smaller duct. You may have to add additional gates in the larger branches or provide another way of adding resistance to them to get air to flow throuhg the smaller duct.

[mark a stephens]

Hi Alan


I really appreicate your taking the time to reply (and I do have "Alan pneumatic gate envy"!)


This is something I'll be playing with... I'm not going to build the ten manifolds needed right away! An A/C muffin fan and voltmeter (plus enclosure) makes for a poor mans anemometer so I can build a more traditional and a box manifold and see how bad is bad. And when I purchase a disk sander, I'll try that home brew PVC manifold too.


The diagram was probably not the best example. I would prefer to have the input ports directly opposite the 6" outlet, if possible. A better example would be a 5" and 3.5" diameter intakes at the rear. Dust will probably collect so perhaps a sloped bottom might help.




thanks


mark

[Kent A Bathurst]

FWIW - I have a rope and pulley system to operate one blast gate. It ended up needing to be where it is very inconvenient to access. Rope goes up to a joist, across, and then down. To "lock" it in open, the rope descends from the overhead joist thru a board cut with a vee-notch [think of a boot puller]. A knot in the rope catches in the vee. And - to be sure it drops closed when I release it, I dug out the surf fishing tackle box, and pulled out a pair of 4oz lead pyramid sinkers. Set 'em on the concrete floor and pounded on them with a mini sledge until they were reasonably flat. Drilled a hole in them, and threaded them on the rope at the blast gate. Works great.

[Thomas Hotchkin]

Mark
Here is a good link for low lost manifold from pvc http://www.harderwoods.com/pipe.html Tom

[Bruce Seidner]

Is there much difference in the behavior of a 45degree wye manifold (created by this program) that was closed off on the lateral end, essentially creating a 45degree elbow, compared to a "true" 45 degree elbow?

What is the radius of the branch coming off the lateral at 45degrees using this program?

Inquiring minds (that can't do the math) would like to know.

[Alan Schaffter]

You can make PVC wyes and manifolds with a lathe. Turn a block of wood the same diameter as the main or mount a piece of the main pipe in a lathe using plugs in each end, a large chuck or Cole chuck, etc., cover its surface with sand paper, and use that to sand a matching profile in the end of the branch pipe at the desired angle. Once the end of the branch is shaped to fit the main, trace its outline on the main and cut the opening. Glue the two parts together.

There is probably a way to make templates like Harderwood's using SketchUp, but I couldn't find it.

[Alan Schaffter]

Is there much difference in the behavior of a 45degree wye manifold (created by this program) that was closed off on the lateral end, essentially creating a 45degree elbow, compared to a "true" 45 degree elbow?

What is the radius of the branch coming off the lateral at 45degrees using this program?

Inquiring minds (that can't do the math) would like to know.

I don't know how much, but there will be turbulence created as the air flows past the opening to the blocked branch.