Help with orifice calibration

[cspeier]

Question Larry, Sould the exhaust side numbers be higher in a perfect world? I was looking on some old 601 flowsheets, on #5 the intake is 456 cfm and the exhaust is 483 cfm. Just curious.

Chad

[larrycavan]

It depends on the coefficient of discharge of the hole. It can be higher in one direction that the other.

A SF110 flows higher on the exhaust using the same calibration plate. The plate is sharp edged on one side of the hole and slightly beveled on the other. You don't turn the plate over for exhaust flow tests. It comes gasketed on one side.

Here's some archive data from the forum. I believe Tom V. performed these measurements.

The Super Flow 300 & 600 use the same 246 manometer but with the
.826 fluid and 1.91 fluid respectively

Going from the .826 fluid to the 1.91 fluid increases the range by 50 percent.

The SF benches had the following ranges:

SF 300 #1 = 25 cfm SF 600 #1 = 37 cfm
SF 300 #2 = 50 cfm SF 600 #2 = 75 cfm
SF 300 #3 = 100 cfm SF 600 #3 = 150 cfm
SF 300 #4 = 200 cfm SF 600 #4 = 300 cfm
SF 300 #5 = 300 cfm SF 600 #5 = 450 cfm
SF 300 #6 = 400 cfm SF 600 #6 = 600 cfm

in each case the orifice holes were the same diameter, they
just changed the fluid to allow 50% greater readings.

Example:
50 cfm time 1.5 = 75 cfm
200 cfm times 1.5 = 300 cfm etc.

Orifices measured on the 300 and the 600 one time and they were the same.

The sizes were .857, 1.227, 1.770, 2.507, 3.059, and 3.490

The flow readings for the 600 chart showed the flows to be:
35.5, 71.5, 151, 299, 451, 604 cfm

You do the orifice size vs the flow and the discharge co-efficients were:

.593, .583, .593, .584, .592, .609

[larrycavan]

I took another look at your second photo. Pictures can deceive the eyes but if you look at the orifice hole edge, in the area i would call top left corner of the hole. It looks like it's bent slightly upward. You see a woodscrew inside the hole...look to the left of it on the edge of the hole.

If it is deformed there, it's going to cause a flow difference on exhaust. I would suspect that alone would make it flow more than intake.

[cspeier]

This is what I come up with.

Int cfm Exh cfm
#1 46.5 97
#2 89.9 177.2
#3 128.9 191.4
#4 174 224.1
#5 248.5 291.2
#6 290.1 345.6
#7 331.6 354
#8 480 449.6

The problem was my "trick" needle valve system. I by-passed
it and the manometer started acting normal. Tried to be cool, and cost me! How do the numbers look? I have a flow efficent on my software called, bench orifice flow coeficent. Is this helpful? THANKS LARRY!!!

Chad

[larrycavan]

Not to worry. You're a pretty sharp guy. My money is on you figuring out what was wrong with the trick valve system and making it work..

As for the numbers. All I can say looking at them is they look reasonable except I'm wondering about the last pair [are they reversed] but what good is that to you?

What your calibration plate flows and the results you got compared to it are the elements of sorting out your ranges.

Here's a spreadsheet. Just plug in your calculated range numbers and what the calibration plate flows.

[cspeier]

Thanks! I'll play with it tonight.

I think the problem is in the needle valve itself. I'm thinking the exhaust side has too much pressure for the valve and it's leaking by. The intake side is dead on. But when I reverse it, it gets crazy. It's a nightmare, hoses all over! Also, thanks for the kind words on the bench. It's been a blast building it. Here's a photo of my nightmare.. Again, thanks!

Chad

[larrycavan]

Chad,

You're more than welcome. Glad to help in any way I can. I'm glad this board is here. My most frequently visited place on the Internet.

Here's a simple schematic of a manometer switch that you might be able to build. No needle valves required, just a good seal and it operates by simply blocking and unblocking holes.

[cspeier]

I'll try it, thanks..

So you have a orifice type bench? Have you seen or had the Merdog plans? What about the Merdog software? I've been really considering a PF box, I think Mouse is the man behind it.

The funny thing about a homemade bench, I'd like to build another one. Seems something can always be changed.

I made this comment on the Speedtalk forum, that it didn't matter to me if digital was better than visual. It didn't matter if pitot was better than orifice. Nothing matters! All I know is my $3,000 dollar bench is within 1% of the $12,000 SF600 with Flowcom across town. BUT, that statement was before my exhaust ordeal. I'll figure it out.. won't stop until I do!

[larrycavan]

I bulit mine over 10 years ago from the PH article. John Clark of MSD was behind the design. The article came about by chance. I have the digital copy if you'd like it. Same thing as the Mercdog.

I modified mine with a new top plenum and intake baffel this spring. It's similar to what the SF600 top is.

Sounds like yours has worked out pretty well.

Larry

[cspeier]

Thanks Larry.

I had some issues to work thru. I had the wrong fluid in the vertical, made my numbers look REALLY good. I changed it to water and dye and killed 20 cfm. Not a problem, at least I know. I wish I hadn't of spent the money on the Dwyer manometers. If I would've found this forum earlier, I would've went with a PF box, still might. Overall I'm really happy. It's been a challange to get running. So many concepts, so many ways to acheive the end result. Like I said, AMEN to this forum. I'll be hanging around.

Chad

[larrycavan]

Chad,

I may end up adding the PF setup myself. I've read nothing but positive comments about it.

Can you post the hole sized and flow ranges for your flowdisk?

Who made it?

Larry

[cspeier]

You want the diameter of the eight holes? Don't want to sound stupid, but how do I come up with flow ranges?

I made the disk myself out of .060 steel and a plasma cutter.

Please tell me what you need and I'll gladly post it.

Chad

[larrycavan]

The size of each hole and how much air it actually flows.

[cspeier]

Another question, with my .985 plate or what? I guess I'm confused!

I have access to a SF110 flow plate. I think it has a .312 and 1.875 hole. Would this work for me? If so, could you walk me thru it? Also, have you seen the Merdog calibration sheet. I'd post a excel copy, but I'm not sure how. If you haven't seen it, I'd like for you to take a look. I can email to you if your interested. Thanks


Orifice Orifice Dia. Orifice Area CFM@28"
#1 .922 .668 61
#2 1.300 1.327 121.3
#3 1.530 1.839 168
#4 1.830 2.630 240.3
#5 2.043 3.278 299.5
#6 2.295 4.137 377.9
#7 2.555 5.127 468.4
#8 3.098 7.538 688

Also, the software will calculate different depression. example

10" bench will flow 832
15" bench will flow 679
20" bench will flow 588
28" bench will flow 497
36" bench will flow 438
42" bench will flow 406
I pulled these numbers from a old calibration form. The actual for my bench is appox. 17 cfm lower.




Chad

[larrycavan]

Chad,

I'd like to have a look at that. I'll send you a personal message witn my email address.