John, your system will have a unique flow coefficient that cannot be calculated or anticipated. The location and dynamics of the two pressure tapping's will also add to the mystery.
There is nothing really wrong with placing an orifice in a pipe, except it will have an unknown and incalculable result. Different sized orifices will behave uniquely and not in any fixed relationship to orifice diameter.
Inclined Manometers - Should they go up or down?
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by 106-1194218389 » Wed Dec 12, 2007 1:29 pm
Got it! I also verified Rocco's spreadsheet is right on comparing to a Superflow inclined manometer. Thanks Rocco! You provide us with some great helps. I thought it may be the way the flow tube works - I noticed also that I do get better results if the orifice is smaller in comparison to the tube diameter and also going to a bigger tube seems to help. I will put my main focus on the bench from Bruce's plans I bought and not worry too much about my inclined manometer with the tube then. Thanks Guys, and thanks Willy as I know you are watching. I just want to publicly thanks Bill Jones as he has been a great help and inspiration to me in my air flow projects.
- 106-1194218389
by Tony » Wed Dec 12, 2007 5:08 pm
That is certainly how it works John.
The larger the pipe diameter and the smaller the orifice diameter, the more closely two otherwise identical orifices will flow in the comparison test. Taking this concept further, the pipe diameter could be made so large, it is no longer really a pipe at all, but becomes a large volume low air velocity settling chamber.
Comparing two orifices is a wonderful test for an orifice bench. If your largest measurement orifice flows the same as an identical test orifice placed over the test hole, then you can be sure that all the smaller size measurement orifices will behave themselves, and flow pretty much exactly according to their predicted flow versus diameter.
The largest orifice at maximum airflow is always the biggest problem and the most difficult to get working. Do whatever needs to be done to improve that, and you will be miles ahead. It may require a baffle, a flow straightener, a large area screen with many small holes mounted right across the settling chamber, or whatever. But it is well worth the trouble to carry out the orifice comparison test.
In my bench the orifice sizes are all in the ratio of 1.00 1.414 2.00 2.828 and so on upwards. Each orifice steps up twice in flow number. This only works if each orifice flows predictably with diameter change.
Another test is to flow something that can be measured on two different ranges. How close the readings actually end up, is another measure of confidence in your bench. If everything falls into line and behaves well, you can be pretty sure you have a stable repeatable bench.
If all the numbers are "wild" and all over the place, then obviously something somewhere needs work to put right.
The larger the pipe diameter and the smaller the orifice diameter, the more closely two otherwise identical orifices will flow in the comparison test. Taking this concept further, the pipe diameter could be made so large, it is no longer really a pipe at all, but becomes a large volume low air velocity settling chamber.
Comparing two orifices is a wonderful test for an orifice bench. If your largest measurement orifice flows the same as an identical test orifice placed over the test hole, then you can be sure that all the smaller size measurement orifices will behave themselves, and flow pretty much exactly according to their predicted flow versus diameter.
The largest orifice at maximum airflow is always the biggest problem and the most difficult to get working. Do whatever needs to be done to improve that, and you will be miles ahead. It may require a baffle, a flow straightener, a large area screen with many small holes mounted right across the settling chamber, or whatever. But it is well worth the trouble to carry out the orifice comparison test.
In my bench the orifice sizes are all in the ratio of 1.00 1.414 2.00 2.828 and so on upwards. Each orifice steps up twice in flow number. This only works if each orifice flows predictably with diameter change.
Another test is to flow something that can be measured on two different ranges. How close the readings actually end up, is another measure of confidence in your bench. If everything falls into line and behaves well, you can be pretty sure you have a stable repeatable bench.
If all the numbers are "wild" and all over the place, then obviously something somewhere needs work to put right.
Also known as the infamous "Warpspeed" on some other Forums.
- Tony
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by ThomasVaught » Wed Dec 12, 2007 5:31 pm
Not a big fan of orifice plates in long moderate diameter tubes. Our Venturi style Ford bench is right on the money consistantly BUT we have a larger calculated/ tested tube diameter for each venturi id to make sure the flows are consistantly on the money.
We use a 30" long "Stack" before a settling chamber/filter and then on to the venturi array. The largest stack inner diameter is 4.64 inches.
I still don't like to test large orifice plates on the stack like you would do the typical "2 orifice plate" comparison test.
When I tested the "Pass Around Plates" the diameters were small enough that the bench read with-in 1/2% of the calibration orifice numbers.
A Lot More to this flow bench stuff than people typically assume.
Tom V.
We use a 30" long "Stack" before a settling chamber/filter and then on to the venturi array. The largest stack inner diameter is 4.64 inches.
I still don't like to test large orifice plates on the stack like you would do the typical "2 orifice plate" comparison test.
When I tested the "Pass Around Plates" the diameters were small enough that the bench read with-in 1/2% of the calibration orifice numbers.
A Lot More to this flow bench stuff than people typically assume.
Tom V.
- ThomasVaught
- Posts: 80
- Joined: Fri Jul 06, 2007 9:06 pm
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