Need some guidance

[The Silver Bullet]

I have three calibration plates for my orfice bench and I am using FP1.
I can calibrate the bench using the calibration plate sent with the FP1 which is 132cfm at 28". This plates calibrates perfectly with a 0.62 CD.
But when I flow a 112 CFM plate it flows high at 118cfm and when I flow a 225 plate it flows low at 213cfm. All measurements at 28".

What would cause such a variance. I have tried different sampling locations, but had no effect.

Thanks for your opinions,
Richard

[bruce]

I would say the machining of the plates might be a problem? Sharp edge or square edge?

[larrycavan]

Are all three plates flow tested using the same range on the flowbench?

[The Silver Bullet]

[The Silver Bullet]

[bruce]

My plates, how can this be

Are the plates being held tight against the bench?

[larrycavan]

Try this.

Calibrate to one of the other plates and establish whatever Cd is required to nail that plate's calibration value. Don't worry if it's not .62.

Then reflow all three plates.

[The Silver Bullet]

[The Silver Bullet]

[larrycavan]

I use a fixed orifice also but there are no studs in the way of the air stream. Nothing to generate any local turbulence near the orifice.

Using a plate I flowed 20 years ago on a Superflow flowbench, I can take that plate, pop it on my stand [same way it was flowed originally] and be within 1CFM every time I test with it. That's my quick test of the bench.

My bench is calibrated with the FP1 calibration plate.

I can pop Bruces 100CFM plate on he bench with no stand and it's very, very, close to 100CFM on my bench.

It's been my personal experience that John's and Bruces plates flow quite accurately. Maybe I should say comparatively to each other.

[The Silver Bullet]

[larrycavan]

Hang in there. Sometimes the initial calibration will give you some grief but you'll nail it down....AND learn some more in the process of doing so.

It's really hard to pinpoint any particular thing in another guy's flowbench. Each one is usually unique in it's design, material, etc.

[The Silver Bullet]

Well I got around to doing some work on the bench this weekend and I am getting closer but not there yet.

I have a 10 cfm leak some where that for the life of me I can not find.
When I "leak test" the bench utilizing a 1/4" hole I am seeing 17cfm.

Is it possible that I am losing the 10 cfm through the unpainted MDF?

I seem to have the calibration nailed down in the lower cfm range (100 -150) but I'm off above 200 cfm. When I flow the 225 plate, I am reading 200 cfm.

Any how I am making progress slowly but surely...lol

[bruce]