flow bench calibration plate

[steve cowan]

hi guys,
just got my new flowbench this week (photos coming)
it has performance trends version 3.5 programme

the question i have is -
do you guys check calibration with flow orifice on top of head fixture or do you take the head fixture off everytime
the instructions say to calibrate with head fixture on
i have read in harold bettes airflow book that this is incorrect and the head fixture needs to be removed to check calibration correctly
thoughts and opinions appriciated

steve c

[Carnut1]

Fixture off, sharp edge facing the airflow. Thanks, Charlie

[mag2555]

X2

[DaveMcLain]

Plate goes straight on the bench, no fixture. Also if its a Superflow the plate that they send with their benches is not really intended to be an accurate calibration plate. It is intended to be used to make sure that the bench is working correctly. I would recommend getting a few plates from PTS to use for calibration they are inexpensive and accurately made with a sharp edge orifice.

[WeingartnerRacing]

On my superflow. The pts calibration plates read low but when you bolt a head up it flows pretty close to what they do on a bench that reads accurately with the calibration plates.

[Carnut1]

On my superflow. The pts calibration plates read low but when you bolt a head up it flows pretty close to what they do on a bench that reads accurately with the calibration plates.

I just set my bench limits to the pts plates and what it reads on the heads is what it is. I figure that is as close to perfect as I can do at this point. Thanks, Charlie

[Sir Yun]

Do you have a set of PAP plates of just one ?

If you have a set you can just do a regression and a R^2 and if needs be correct it a bit ( the plates are a sort of reference to a bunch of benches including one in a lab that uses NIST venturis, maybe not perfect but cheap and it will give you a better way to keep things more honest than using just one point)

[steve cowan]

thanks to all,

you will have to bare with me gentlemen as this is my first rodeo
the test plate that was supplied is a piece of acrylic plastic machined out to 2.173''
stamped 365.4 cfm @ 28''
it has sharp edge both sides
the machine was calibrated a couple of weeks ago in a different state (postcode,zipcode )
it has a correction factor of 1.08
i assume that i have to test calibration every other day due to weather changes?
this is all electronic and i do not have to calculate anything myself
i understand accuracy and repeatabilty are of concern
i am not porting or flow testing heads from a profit point of view
just a guy in the shed trying to learn a couple of things
thanks again for input

steve c

[Rick360]

I've said it before but I'll say it again ... Don't "calibrate" your bench with plates on top of your bench. As Erics's tests have shown plates don't flow the same on every bench. It depends on many things of how the bench is constructed. The thickness of the top plate and/or the hole diameter and shape will have a BIG effect on the flow of an orifice mounted on top. See the thread Eric W. posted about his benches as his tests confirm exactly what I have seen.

steve,
If you have a typical orifice type flowbench, there is no need to flow test a plate regularly or check weather etc. These type benches will/should read the same in different weather baro/humidity/temp and need no compensations. Did you call the person who built the bench? to ask about the plate that was supplied?

Rick

[pcnsd]

As Erics's tests have shown plates don't flow the same on every bench. It depends on many things of how the bench is constructed. The thickness of the top plate and/or the hole diameter and shape will have a BIG effect on the flow of an orifice mounted on top. See the thread Eric W. posted about his benches as his tests confirm exactly what I have seen.
Rick

I am not certain I can agree. What an sharp edge orifice plate flows at a given pressure differential is a matter of physics and it's design. My understanding is 2% of value is the expected variation. Identical calibration plates should flow near identical CFM within that range. That different benches interpret this as different flow volumes outside of that range is an issue with the bench not the orifice. I would be interested in a link to the referenced thread. I have a spreadsheet with the equation to determine the flow to area relationship. There are relatively few inputs that an average technician might tamper with other than air density.

[Rick360]

As Erics's tests have shown plates don't flow the same on every bench. It depends on many things of how the bench is constructed. The thickness of the top plate and/or the hole diameter and shape will have a BIG effect on the flow of an orifice mounted on top. See the thread Eric W. posted about his benches as his tests confirm exactly what I have seen.
Rick

I am not certain I can agree. What an sharp edge orifice plate flows at a given pressure differential is a matter of physics and it's design. My understanding is 2% of value is the expected variation. Identical calibration plates should flow near identical CFM within that range. That different benches interpret this as different flow volumes outside of that range is an issue with the bench not the orifice. I would be interested in a link to the referenced thread. I have a spreadsheet with the equation to determine the flow to area relationship. There are relatively few inputs that an average technician might tamper with other than air density.

Everything around (before and after) an orifice will alter the flow thru it. If the flow thru an orifice is fixed why can't you use it on top of the head fixture to check your bench? Because the cylinder CHANGES the flow thru the orifice. It's not a small amount.

Rick

[gnash]

From the Flow Performance web site --

"Flow bench adapters are part of your test piece. They are not part of the flow bench. They are a component of the test and should be documented in detail."

[larrycavan]

Actually, the amount of flow that the bore adapter [test stand] affects the flow will vary depending on the relationship of the orifice being tested to the size of the bore. It can be a small amount or it can be greater. The close the diameter of the orifice to the size of the bore adapter, the greater the influence the adapter has on the readings. That stated, you don't INITIALLY calibrate with the bore adapter installed unless the calibration plate you have was calibrated that way...NOT LIKELY TO HAPPEN.

First realize that the calibration plate value you get should be accompanied by the conditions under which those values were obtained.

For speed sake down the road, after calibrating using the standard method, [test stand removed], attach your flow stand and then reflow the same calibration plate on top of the stand. Note your readings. Those will be your quick reference numbers for assembled checks. Use them as a quick check with the test stand and same bore adapter assembled.

As a side note, Temperature and Barometer do play into the calculated CFM value. In theory, the ratio metric type flow benches should be able to be calibrated at temperature xx and barometer xx then moved to any other location and the readings will still be the same if you flow tested the same calibration plate.

What ratio metric doesn't mean is that calibration plates with values established at temperature xx and barometer xx are guaranteed to flow the same if moved to another location where temperature and barometer are different. Best to know the source data of the established CFM calculation and then you can account for location variations.

The larger the orifice, the greater the variance in calculated CFM when temperature and barometer differ significantly.

[Rick360]

How do you explain Eric's test with the plate vs tests with the same head?

The problem is that all benches aren't built to the same dimensions. The top plate thickness may be different, the opening will be a different diameter, different exit shape, the upper plenum size and shape have an effect, how far are any diffusers or the measuring orifice from the top plate ... and the list goes on. All of these things alter the flow thru a "calibration" orifice mounted to the top plate and will make your readings different when flowing a head if you set your bench ranges based on that "calibration".

I'll bet if Eric measured some of those areas mentioned on both benches he would see some differences that are likely causing the differences.

The simplest calibration for a home bench is to take a head to a known flowbench and get flowz at different lifts using all ranges somewhere in the lift range and flow it on your own homemade bench and adjust your range until you agree closest to the known bench. Make sure to duplicate as much as possible ... bore size, radius entry etc.

Rick

[steve cowan]

hi guys,
a bit of an update,i figured after my post that the flow bench manufacture who has been building flow benches for 20 years must have a good idea what he is doing
his instructions do say to check calibration with the sharp edge plate with the head fixture on
after reading a fair way through performance trends port flow analyzer manual(page 147)
using a custom bench with the 3.5 programme to check with a sharp edge orifice with head fixture on
i am putting up the pages from both manuals,sorry for the glare from the photo flash
i have not rang the manufacture because i believe i have to persevere for a few weeks at least
thats how we learn
thanks for your posts as i think it is a very interesting subject,hopefully i have not bitten off more than i can chew

steve c