Flowbench Spreadsheet???

[Thomas Vaught]

You get my e-mail?

[86rocco]

Yes, didn't you get my reply?

[Thomas Vaught]

Your original spread sheet was sent to my home.

I forwarded to work and modified it.

I sent it back to you from work.

I am at home again.

I will look for it tomorrow.

Thanks for your help on the spreadsheet.

[RRBD]

Rocco,
In that spreadsheet, I noticed that there was a value of 28" put in the one field....now I'm confused ,shouldnt that value be a calibration value based on the height of your inclined manometer at 100%?? I thought you "calibrate" your orifice to the amount of vertical rise on your flow meter. Am I washed up here. I thought the "big numbers" were for depression just used for base lining your tests. I have read alot on the forum and for some reason this is how I come to understand it.

Please correct me, I feel like Lenny from "Of mice and men"
Oh George, please tell me about the orifice calibration one more time George........

RRBD

[86rocco]

The point of this spreadsheet is to generate a scale that you can use with an inclined manometer, in the example in the spreadsheet, the tube used for the manomoter is 28" long, the height of the incline is 12" and the numbers generated are the distance measured along the tube from your zero point.

I'm sorry for the confusion, 28" was perhap a bad number to use for an example but that just happened to be the length of the tube I was using on my prototype at the time I developed that spreadsheet for the proposes of the spreadsheet, it could have been any length.

[Christian]

[color=#000000]Well i do have my formula out of peter burgess book, but made some concessions to what seems to me mre reasonable, since he uses on his plans just one orifice. anyways, one needs the valvediameter since it compares the flow through a ideal hole(orifice, somewhat ideal)to a valve with kown diameter. Seems to work ok with me, didnt have the time yet though to bring in densitydifferences (warm to cold days), but

[86rocco]

With an orifice type flow bench, you don't really need to correct for air density because as you say it's comparing the flow through a know object i.e. your orifice to that of an unknown object, your test piece, and since the effects of air density is the same on both sort of they cancel each other out so on the percentage scale of the inclined manometer, the piece should test the same whether it's a cold day or a hot one.

IWO, while the actual amount of air flowed many vary from day to day due to change in air density, the reading on the flow bench should not. We pick an air density to calculcate the calibration of the orifice at, commonly .07484 lbs/ft^2 and all of our readings are relative to those conditions.

You may say "but then we don't get true CFM reading" and you'd be correct but we do get consistant reading so that we can have confidence that when we make changes to our test piece, the changes in our flowbench numbers are a result of those changes and not just a change in the weather

[RRBD]

Rocco, I was asking about the orifice flow spreadsheet, thats the one with the 28" that I'm confused on. Please pipe a little sunshine my way.....

Scott ???

[86rocco]

Again, 28" is just a number, you can put any number you like in that spot of the spreadsheet.

But what I think you're really asking about is calibrating the flow bench. The way I would calibrate my flow bench would be, as you suggest, to first calculate a value for 100% on your scale based on the height of the inclined manometer then I would place a test orifice of known size on the flow bench, where one would normally put a cylinder head for testing, run the bench up to its normal test depression, 10", 28" or whatever you'd normally do when testing a cylinder head, calculate who much should flow through the test orifice at that depression then check the reading on the inclined manometer scale and compare the numbers you get from that to the calculated amount for the test orifice, this will help you to account for any anomalies on the bench such as leakage around the orifice etc.

[Christian]

[color=#000000]Rocco
HHmm, Hhmm sounds reasonable to me, but on hotter days isnt there less flow on both holes (simple said)? just because both show the same pressures as on cold days does it also mean they have the same massflow, evwen though it

[86rocco]

The density of the air does vary considerably with temperature and barometric pressure and with it the amount of air (both cfm and mass) that will flow through a orifice at a given depression. But knowing the actual amount of air flowing on any given day is usually less important than generating meaningful flow numbers that we can compare with those taken under different conditions without having to calculate correction factors to account for changes in air density. My point is that we can "standardize" our flow readings by calibrating our flow bench orifices assuming 100% air density and so allow us to confidently compare two flow numbers even though they may have been generated under different condition.

[RRBD]

Thanks Rocco, I thought I was starting to slip......
Scott

[Christian]

[color=#000000]To be honest i still dont get the hang of it, Lets say you have a reading say during winter lets assume 100%density, you make a flow chart, then you port the head, and test it half a year later during hot summer, assume 80%density, wouldnt i have a huge bias, where i couldnt tell how much the exact repeatable increase through porting is. I assume the valveflow coeefficient

[86rocco]

[Christian]

[color=#000000]HHm i took a look afterwards at my equations and found also those results, since density and temperature will be put in afterwards, all i do is basically relate my valve flow to the flow of a somewhat kown orificecoefficient. Hmm hmm sound reasonable now. Thanx. So basically i can compare heads by CD