Calibration - with our with out bore fixture

[alex]

Just curious if anyone has noticed different cfm reading through a calibration plate with out a bore fixture attached and then attached with the plate now on top of the bore fixture? i have found slight differences in cfm between the two.

Thanks,

[106-1194218389]

How much difference did you get?

[115-1172523331]

I'm still working on "stabilizing" the manometer readings, but that was next on my test plan. Right now I am testing with the calibration plate sealed to the top of my bore adapter holder. (See pic) I was wondering if the "step" at the edge might be influencing my flow rates as I am 3-5% low. I'll try to test before leaving on vacation on Thursday. -- Doug

[alex]

with the bore adapter attached i see about 10 cfm more and i have tested the leak to be zero with out with out. can the extra height of the bore adapter be the cause? i have also added flow straighteners inside my flow element but have found the same results.

[thomasvaught-1]

On the high dollar Ford bench I have to pay attention to the orifice size being tested vs the "stack diameter" The stack is the same thing as a LOOONG bore adaptor. The length typically is not the issue BUT THE DIAMETER OF THE STACK IS.

When the orifice hole to Stack diameter is ratio is off (orifice too big for diameter) the readings will not match closely the numbers from the forum spread sheet. That spreadsheet is a nice checking tool IF you make sure you put in the right Lbs/cubic ft for your local air density.

Tom V.

[GordonE]

I have also had problem when the calibration plates is getting close to the bore size.
I have a 96.5mm bore and uses three plates.
21.494mm, 37.22mm and 52.65mm. When I first used a simple formula without concidering the bore I thought they would flow 51.4; 154.1; 308.3CFM

But somehow the bigger plate did always read higher. I can add that my plates are square eged. Thera are just 3mm plates that are machined straight thru.

I now use a calculator to calculate the flow of my plates. I am not sure if this is the appropriate way, but now all three plates read within 3%. The readings that I should have according to the program is(readings my bench)((spradsheet calculator)):

307,3 (307) ((308.3)) (calibrated on this plate) 99.9%
147,4 (146) ((154.1)) 99%
48,5 (47) ((51.4)) 96,9%

The procentage represent the differens between my readings and the calculated values of the orifice flow calculator.

I use this calculator:


I would be glad if someone more could give their opinion on this... I dont say that this is the right way in numbers, but It give a linear curve for me. It gives approximatly 5% lower values than the spreadsheet on this forum with my square cut plates.

Regards Gordon

Hope this helps you some...

[jfholm]

Can you guys see the post I made with all my readings? It was a long post and all of a sudden I got a funny IKON Board message and it dissappeared? I cannot see it but it was saying that I had made a post.

John

[bruce]

It was there and then when I came back later it was gone ???

It's not showing now

[jfholm]

The IKON Fairy got me I will repost tonight when I am at home

John

[bruce]

Least it didn't ZAP you out as a user

[jfholm]

HA HA HA HEE HEE I saw a number 2 and I went there and there was nothing - the fairies are still at it.

[bruce]

Shoulda left this old thread in the "way back machine" . . . :p

[jfholm]

[color=#000000]Here are the results again for the NPS orifices we found at NPS warehouse. NPS buys lost and unclaimed freight and freight damaged loads. These orifices are 4.375" o.d. and .125" thick. They are made of 304 SS. The orifice holes are beveled with a 68