orifice plate leaking

[Nick]

I'm not knocking the FP1 here, just trying to point out that there are limitations to electronics. I would like to own one.

The chances of this thing I'm working with actually working is low, however learning a little about how this stuff works is worth the few bucks I spent. I don't know the resolution of the unit. I don't know how many bit's it is. My knowledge on the subject is limited.

If John wants to share the resolution we can calculate what would be exceptable to each one. Is 2cfm error ok with you, maybe it's not with someone else.

Not trying to start an argument here, I just don't think electronics are as good as some may think. They have limitations, my water gauges do not. It's all how you want to look at it.


If I'm wrong set me strait.



Nick

[larrycavan]

I don't know what your scale looks like but I didn't even bother making single graduations on mine below 15%. There was really no point to it. At nearly 29" of length and 12" of rise the scale certainly wasn't small yet the markings were so close together down on that part of the scale, it would be very difficult to actually view the reading accurately.

If you're saying that your bench is capable of reading that low on the scale and you are certain it's accurate down that low, then you've built an exceptional bench....

Larry C

[Nick]

I did some testing to show my experience with this bench. I have never operated anything else so I don't know how well they work. I've only tested 2 heads, and the results I'm seeing are the same. There is about a 1/16" between the marks between 10 and 15%. I can see that fairly easily. The manometers are very steady, the only time they are not is when there is turbulence in the port I'm testing. My scale is 28" long. I made no marks below 10%.


Orifice #1 #2 #3 #4

.50 57.5%=27cfm 29%=27cfm 19%=28cfm 14%=27cfm
.100 99.5%=50cfm 50%=50cfm 33%=50cfm 24.5%=50cfm

I get the same numbers. So why should I mess with changing orifice positions?

I'm not saying this is exceptional, this is just my experience. Has anyone tried similar tests to see the variance with there bench?


As a side note the incline scale does not have to stop at 100%. Past the 100% mark I ran the tubing vertical up the wall. You can just mark it off, going as high as you want. My ceiling is at 39" so that is as high I can go. Past the 100% mark you can use the Delta P height in your math to calculate flow.



Nick

[DaveW]

Nick,

Is your incline and vertical steady @ higher test pressure with turbulence in the port?

Your bench must be a good design if you can get down to 20 some percent and be accurate. Now you got me re-thinkin my orifice plate sizes. I'll never get done. Thanks for the info.

Davew

[larrycavan]

Nick,

You really can't ask more from a bench that gives numbers like that. It's impressive.

Larry C

[Nick]

[cboggs]

[Thomas Vaught]

Quote:

"I had a friend run my 400 cfm test orifice on his SF300 and it's within 1.5 cfm of my bench @ 28"

Where did he take the reading?

Based on some old super Flow 300 information I did not think the bench would pull 400 cfm at 28" depression.

Tom V.

[cboggs]

[Thomas Vaught]

I do not think the dc will me the same in every case. The SF 600 bench varied from .586 to .604
(.604 was the 600 cfm hole).

Tom V.

[bruce]

Curtis,

Send me the flow numbers you are getting on each of the plates I sent to you. I'll work the numbers and see what I can findout.

[cboggs]

[Mouse]

Curtis,

Keep in mind you are looking to get your bench to flow within a percentage range, preferably within 1%. Exact flow numbers are not practical.

So, with a 90 and 400 orifice, you are looking for flow rates between 89 and 91 for the 90 range, and 366 and 404 for the 400 range. If you can get close to these figures, pat yourself on the back and light up a big cigar, and be confident in your flow bench.

Other than that, your Cd for your ranges can certainly be affected by supporting structures, especially for the 400 range.

John

[cboggs]

John,

Yes you have a good point, .. but I want it to be PERFECT, .. OK, .. so I'm
being a little anal, ..

OK, .. so as an example, .. I take my #4 range that flows 417 cfm @ 100%.

The 400 cfm plate will read 400 cfm if it's calibrated to that, .. but the 90 cfm
plate will only read 82 cfm, .. so is what you are saying is to split the difference
between the two for an average accuracy within 1% ????????

Bruce, .. the plates you sent have a size, a flow rating then a "tested" flow
, .. what did this "tested" flow come from?
I don't know how I ever got along this many years without these plates!

I'm thinking I'll take the plates and flow them all on a few SF-600's, and use
that as the number to calibrate to so my bench will match the industry
standard, ..

BTW, .. you guys are awesome, ..

Curtis

[Nick]

The cd (dc if you want) will be a little lower with the smaller orifices. There should be a place to change the CD in the program. All the stuff I have read on fluid mechanics so far states that you have to calibrate your orifice. There are just to many variables that affect the cd to just say they should all be .62. For starters we should have all are orifices in pipes and the pipe should be a ratio to the orifice, and there should be a long pipe before and after the orifice. But even if you went to that extreme you still have to calibrate to determine the CD. If you look on the site that Tom posted, you will find the calibration could be off as much as 1.5% even at the level that there building to. In my opinion you will not get it perfect. If you had a larger settling chamber before and after the orifice plate that would help. Also sharp edged orifices are not the best at repeating every time. A 1%-2% (4-8cfm on the 400cfm orifice) error in normal from what I have read. That's why that big fancy three million dollar job uses venturi, (spelling?) in pipes not orifices in boxes. So what I'm saying is find a way to change the Cd for the lower range and be happy.

BTW the bench looks great!

Anyone feel free to tell me I'm wrong.

I now under stand why the weather man can not predict the weather for tomorrow!!!!!!!!!!!!!!!!!!!!!


JMO


Nick