Cabinet Leakage - How much should I expect?

[Dom G]

I continue to work on my MSD style bench and am getting closer to the point where I'll be firing it up. In rereading the original design article it stated the amount of cabinet leakage should be under 15 CFM when measured on the smallest orifice at 28".

What amount of cabinet leakage have others found who have already built, tested and are using their benches?

Thanks.

Dom

[Thomas Vaught]

I built a bench like the SF 1200 with a fixed orifice plate
and removalble rubber stoppers and had Zero Leakage.

With the rotating orifice deal and using "marine port hole"
type openings with "o-ring" covers the leakage should be
less than 5 cfm.

JMO

Tom V.

[84-1074663779]

I have no detectable leakage either. My bench uses 1" MDF panels glued and bolted to the outside of a welded steel angle frame. Under Vacuum, all the joints are under very high compression, and there is no reason why it should leak.

Sealing against positive internal pressure is far more difficult because the joints try to blow apart, vacuum is far easier to cope with (safer too).

[cspeier]

I have 3.2 to 4.5 on my MSD style bench. See I can say that with confidence because it's digital...

[Dom G]

It sounds like cabinet leakage under 5 cfm is a more desirable goal.

Tom V, I am using the rotating orifice as described in the MSD plans, but I do wonder what you specifically mean when you
say "marine port hole" type openings with "o-ring" covers?"

Thanks everyone.

Dom

[Thomas Vaught]

See link attached for the SF 1200 bench:



Go to the brochure on the left side of the page and you will see the port hole.

The SF 1200 did not have the port hole access until I "invented" it.

The covers seal very well with the "o-ring" and are cheap, like around $20.00 with shipping. Much less leakage vs the sliding door on the MSD bench.

Tom V.

[cspeier]

What I'm seeing is a round opening that has access to the flow stoppers. This is what you suggest replacing the slide doors on the MSD style bench? They can be had for $20.00 each? That's cool! How does the face attach to seal up. The door style is a PAIN IN THE BUTT!!

Chad

[larrycavan]

The MSD bench can be made leakproof as well. The exhaust door is a culprit for leaks. I moved mine to inside the bench rather than on the outside. Let the pressure help you rather than work against you in such situations.

The only leakage problem I had was not related to cabinet construction. It was internal leakage between the flow ranges. That's another area to improve on.

If you look at a CDROM case as the design element for the flowdisk, you can dream up any number of solutions to a leak proof flowdisk.

Tom...did you work for SF at some point in time?

Larry

[Mousehouse1]

If you are using a FP1 box couldn't you build or make a MSD style bench with one orifice hole? Isn't there a better way to construct the side doors on this style of bench?

[gofaster]

[quote=
Go to the brochure on the left side of the page and you will see the port hole.

The SF 1200 did not have the port hole access until I "invented" it.

The covers seal very well with the "o-ring" and are cheap, like around $20.00 with shipping. Much less leakage vs the sliding door on the MSD bench.

[/quote]

Hi Tom,


Your post has put several questions in my mind:

From whom do you order these "porthole doors"?

Is it feasible to use the porthole doors for the intake and exhaust doors too?

Since you use stoppers and do not have to turn your orifice plate, did you still install the orifice plate at the same angle as the MSD plans call for?

Do you have any pictures to show any construction details?

Thank-you for posting your ideas! I'm fast approaching the start date for building my new bench, and it is exciting to find these new ideas that I should be able to apply to the project. The cabinetmaking class starts the end of next week.[quote]

[Fkned]

[cspeier]

I better clarify that. I set up three orifice holes, 1.250, 2.580, 3.098. The small hole I use to check leakage. The 2.580 I use for exhaust, and the larger for intake. I had a hard time getting the exhaust to work on the larger orifice. However, on either the 2.580 or 3.098 hole, I could flow the entire port on the orifice I selected. The MAIN reason, the dc for the exhaust orfice is much higher than intake. To be honest, the orifice design sucks for that reason. Depending on sucking or pushing, no two holes are the same! Don't get alarmed if you find this, it's normal.. You need to have more than one hole, maybe not seven like my orginal design, but you need some flexability..

Chad

[Mouse]

"the dc for the exhaust "

That should read "Cd" (Coefficient of Discharge).

John

[Jesse Lackman]

Aren't there a few areas of potential leakage?

->Between intake and exhaust sides of the vacuum motors.

->Between vacuum motor chambers and the outside of the bench.

->From the "top" side of orifice plate divider to the vacuum motor chambers.

->From the orifice chamber to the outside of the bench including the head fixture.

The critical leakage areas would be the ones that involve the orifice chamber, right?

Like flow from the vacuum motor chambers that bypasses the orifice in use, or flow out of the orifice chamber that is not passing through the test piece (head).

Leakage between the intake and exhaust vacuum motor chambers doesn't affect bench accuracy does it?

I don't like the orifice disk at all.

I would rather have single interchangeable orifice plates, or a 700cfm Flow Performance Element where the orifice disk goes.

[bruce]

I'm going to play the "devils advocate" and ask why not just build a pitot style bench? No leakage or Cd's to worry about. Couple peices of PVC pipe, some motors, an FP1 with the flow tube or your own pitot and you are testing . . .

I keep reading all the problems you all are having with the Mercdog design and it makes me wonder . . . just asking not trying to get into a "flame war"