Variable orifice material

[SuperRunner]

So I am making a variable orifice, I guess simlier to the new SF benches. I had planed on using either mild steel, or stainless. But, I was thinking about maybe using acrylic or polycarb, probably 1/4 thick. Might make a better sealing surface. What do you think?

[SuperRunner]

I went ahead an bought the acrylic and I went 1/2 inch instead of 1/4. Probably overkill, but I just wanted to make sure.

What I will do, is have a large piece with a triangle cut out, then I have a smaller piece, roughly twice as long as the triangle cut, then cut out an inverted triangle into one of the edges. The two triangles in the 2 pieces will be identical in measurment. I will then use 2 pieces of acrylic on either side of the smaller piece, these will be glued or scewed in place, then I will take two more pieces that will go over the edges of the smaller piece with the triangle. And glued to the other pieces that were glued. It will be a snug fit, and the smaller piece will slide inside these groves that were just made. Then I will use a rack and pinion design to move the sliding piece in and out of the groves, opening and closing th hole that the 2 triangles will make......make sense?

I will have to draw up some diagrams and take a picture when it is complete.

[SuperRunner]

here is the diagram.

[larrycavan]

I like that concept..looks like the SF1020. I have no idea how they are figuring the Cd on it but they figured it out...

When you get that sorted out, let us know. That, to me, is the way to go for a multi orifice bench....

Larry C

[Thomas Vaught]

I did a little cad work and think you need to have two diamonds vs the Diamond and "rear sight" approach you have posted.

I would think that having two plates with the top plate having a bevel cut on top and the second bottom plate having a bevel cut on the bottom would be as close as you could get to a sharp orifice. This would also allow flow from either direction.

Tom V.

[SuperRunner]

not sure what you mean by diamond...because the opening is actually is actually a diamond, and the diamond will either get bigger or smaller. You are right about the bevel, I will need to bevel both sides to get a sharp edge.

I was just thinking about calibration though, if I had a set of calibration plates, I could just calibrate it before every time I use it, instead of having a set position for each setting, I just re-calibrate? Would that be a waste of time, or might that give me slightly more accurate numbers?

[larrycavan]

[SuperRunner]

I am using a rack and pinion and reduction gears. The rack and pinion uses a ratio so that one full rotation will open or close the panel to closed or full rotation. A solid rod will go from the panel to the pinion gear, and along that, I will weld on a disk will be flush against a piece of metal(will probably also act as my baffle), which is where I will have my detent ball located. This rod will then go through my control panel with a indicator as to what CFM it is at. I will then use a 5 -1 reduction, and every half of a turn will be 50cfm...or whenever I hit the detent ball location, for a total of 10 CFM ranges. I am going to have to calibrate it for each setting though.

[Scott]

I got this all planned already, it would be very thin as well. I didnt notice all this going on. For adjusting ranges you can use a ball detent, with a pull rod that has sequenced spot- drilled pockets. The set up I designed will only be 3/16" thick and flat on both faces. I'll get one built as soon as I get caught up with customer stuff. I'll post pics, and maybe sell a few. I think it will calibrate easy as well.

Scott

[Thomas Vaught]

I was just thinking about the transition into the sliding diamond. For a portion of your test ranges you will be "falling off of a cliff" on part of the diamond and the other half you will be basically like having a calibration plate on top of a bench. It may not me too much of an issue if the upper fixed plate is fairly thin. You mentioned 3/16" thick plates.

Will be interesting to see how it works out. I guess you could make a similar "half moon" deal on a normal orifice plate and see if the flow changed much there by having the "cliff"

Tom V.

[SuperRunner]

I didn't think of the cliff deal. Maybe a thinner piece would be better, or I just might need to go back to using metal. Could easly get away with using 1/8" stainless. Means I just wasted about $60 in acrylic :O

[bruce]

One thing to keep in mind and this is a big thing from my perspective on orifice design . . . precision! Your sliding mechanisim is going to have to hold your pieces to a very small tolerance of .000" if you want any repeatability out of it.

The Cd is going to change over the different ranges due to the sliding parts over lapping and having different edge surfaces (its tough to beat a sharp edge orifice for repeatability, unless you use a pitot style bench). The dent locations are going to have to have no "slop" (hey I live out in the country, and I'm a tractor puller, speaks for itself) in them at all to hold .000". Anything more and your readings are going to be off from one test to the next without calibration (gonna need a set of my calibration plates)

So what do you gain by having a sliding orifice if you have to be calibrating everytime you test? Just my thoughts on the whole thing . . . if I had more free time I'd do a little looking myself into it

[Mouse]

I think it could work very well if you had electronics that could calculate the flow rate through the VO (Variable Orifice) as it is changed. I think it could be done, but I wouldn't want to try it without electronics "doing the math" in real time for me.

I think a sliding strip of metal with orifices in it would be a better method without electronics. Like film in a camera, you just pull the strip from side to side to select an orifice.



Edited By Mouse on 1141572507

[Thomas Vaught]

I agree with Mouse. Much easier to seal as your largest hole might be only 4" and a 6" seal around the perimeter is much easier to seal vs a large orifice disc. Calibration would be the same as a single orifice. You could still use your rack to quickly move the "strip" to the next orifice position.

Tom V.

[SuperRunner]

Yeah, something like that might work, instead of a variable orifice, you have a slide select. Similar to the rotating disk, but it would use a much smaller area for sealing. I might just stick with a simple design as to stick in a calibrated plate. Take just a few minutes to change with an 8" deck plate.