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 Flowbench 101 
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Joined: Fri Feb 17, 2012 10:18 am
Posts: 81
1960FL wrote:
Buddy you do not understand the functioning of the bench, 28" is your test pressure and has nothing to do with the Flow of the bench. The plates that are marked @ 16” are the ones that dictate the MAXIMUM flow range of the bench when used inside the bench.

So in your example your 450@28 plate is only good to 340CFM when used inside of the bench! As the DM flow sensor CANNOT read more than 16” across the plate.

You can test parts at whatever depression you want but the CFM markings @ 16” on the plate dictate the Absolute MAXIMUM CFM FLOW through the bench when used inside.


PS Please play with this spreadsheet and learn to understand the affects of pressure on flow through the orifice.

Rick , I think I my have asked my question wrong . But you have cleared up my confussion on the 16" inside . I understand the flow inside can only do what the orfice plate will allow or it can damage the DM . If i'm thinking correctly my test part cannot flow more that the orfice plate is rated for at 16" .I think I was confussing the test flow and the bench flow as the samething.It would be two differant flow rates , correct? I some times type things wrong .I will keep trying to read up on this to understand it better , thank you.

Tue Mar 05, 2013 5:14 pm

Joined: Fri Jan 08, 2010 10:36 pm
Posts: 1118
Location: Maryland

Please don’t take me wrong this is just and issue with many people on the forum and I cannot say it enough one has to understand the relationship between Depression and Delta P. And they must have a good grasp on understanding the correlation between Pressure across the orifice (Delta P) orifice diameter and lastly the CD.

If you spend time in the spreadsheet (Thanks again Ed) and play changing pressure and orifice size you will start to get a hold of it. You will hear on tapes, talk on the forums and in performance books the use of a flow value for 1 square inch @ 28”; It is most often posted as 147CFM but that equates to an orifice of 1.128” at 28” using a CD factor of 1.0 or perfect theoretical flow. You can use this sheet and the formulas within it to evaluate your port performance, I/E if your port had a MCSA of say 2.0 Square inches and your port flowed 230 CFM your port would have a CD or .78 or 78% of the theoretical potential flow.

I hope this jogs the brain and helps in some manor.


We should probably move this to another thread

Tue Mar 05, 2013 6:24 pm

Joined: Fri Jan 08, 2010 10:36 pm
Posts: 1118
Location: Maryland
I cam across this video doing some other research and find it appropriate for this FlowBench 101 section as it provides and excellent description and visualization of Orifice plate and venture measurement in operation and a good visualization of the Vena Contracta.


Last edited by Brucepts on Wed Nov 04, 2015 7:45 am, edited 1 time in total.

edit to add the video embed

Tue Nov 03, 2015 9:11 am
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