design issues

[jfholm]

Larry,
The Audie unit uses a pitot inside a 2" or 3" PVC pipe or for high flow can have two tubes.

I had one of the early versions and it worked great for a few years. The last little while it would not read above 245 CFM no matter what head I tried on it. Audie Thomas was very good to try and help but I never could get it fixed and that is what led me to this forum.

Keith,
calibrating with the orifice on top of the cylinder adaptor will affect the flow readings of the orifice.

John

[49-1183904562]

[slracer]

Larry, I used an Audie system a friend of mine loaned me before I started building my pitot bench. The way I remember it, Audie uses an orifice in a pipe as a calibration/setup tool but removes it for the actual testing. This is how the atmospheric changes are handled. You calibrate the flow with a dial on the front of the control panel and the electronics then allow you to output the actual flow value at whatever depression you are getting or the value of that flow when converted to 28" H2O. John, if I have that wrong, feel free to correct it as I have slept since then and sleep erases my memory! :p I also don't remember if the actual depression value is available? Although we are familiar with the problems of an orifice in a pipe, in this case I believe that a well produced and calibrated system used as it is will probably work well. (Actually, in this case, it sounds like Keith isn't using that part of the system?) Audie's writeup is here:
but without the internal details.

Keith, I am looking at the pics you posted (very nice looking bench, by the way) and am trying to follow a flow path. Looking at the 2 major tubes on the back I assume you are flowing both ways using the Audie as your "averaging pitot" setup. Where is that piece located? Wherever it is, Larry's suggestion of a top plenum is a good idea! You want to take your static pressure in a non-turbulent (and as close to non-moving) area of the flow as possible and the short distance under the adapter is causing a major amount of turbulence! You don't need the other mods as they were to clear flow through the orifice (which you don't have). As I remember the Audie setup, there were small flow straighteners at both ends. I would add some more length to those if possible as you want the flow through the measuring section as clean as possible. Here is the writeup on my bench explaining a bunch of things you may want to consider.


The whistle noise is not new here, but I cannot find the thread right now that talked about causes and fixes. I'll keep trying, but if you can't wait, try searching through the archives. I know there are some comments in there somewhere! You could help with a bit more explanation on how you are using your "black box". Are you adjusting motor speed so the actual flow and flow @ 28" are the same or getting it close and letting the electronics take over or ?

Looking forward to more pics (overall shot and others). Good luck! -- Doug

[jfholm]

Doug,
That is how you calibrate it, with the orifice in the tube and it worked fine. There were two ways of testing with the Flow Quik, adjust depression every lift like you do with the orifice benches or just run it full tilt and let the Flow Quik correct it to 28" - both the software and the unit itself (I think the unit will) give you a read out of actual depression.

btw On my Performance Trends Black box I can just crank it up full tilt on my vacuums and it will correct also to 28" H2O. I have done that and it seems to be ok just the noise drives me nuts.

John

[K-Star Automotive]

I'll get some more pictures posted.

I am using a motor controller to get my 28" depression.


Let me go a different direction for a second.

For all the guys that calibrate your bench's. If, for converation sake you have the calibration plate centered on the opening and it reads 100cfm, if you slide it foward or backwards to it's extreme does it change the number?? If so, by how much???

Keith

[larrycavan]

[K-Star Automotive]

Larry, I am thinking along the same lines. I did a rough trig calculation and my vacuum port is only at a 3 degree angle from my opening. If i would raise the top plate 5" then it would be at more then a 15 degree angle. The chamber on the top of the bench is only 4 1/2" deep. I also thought (as a test) about fabbing some type of smooth raduis pipe to install under my opening and facing it towards the vacuum source to see if it would clean up the noise.

When i slide my calibration plate foward the cfm will change 3 to 5 for the better, if i slide it towards the back of the bench it will loose that amount. Thats why i think it's a turbulence problem. That would also explane the God awful sound it is making.

I was thinking about making a vid of it and post it on you-tube, but i am not sure that the sound could be apreciated.


IMO on a good operating bench you should be able to spin the head any place, as long as the valve to bore distance is the same and get the same readings. I just don't think that a 20 cfm difference is from placement on the bench, but thats me.

Keith

[larrycavan]

100cfm@28" plate on 3" stand

Tested@10" because SF110 limitations

SF110 - 58%/105 - 60.9cfm
On Mine 62cfm
60.9 *1.67 = 101.7cfm
62 * 1.67 = 103.5cfm

move plate fwd, back, lft, rt - so orrifice is about 1/4" from edge of bore wall - 60cfm

Tested on mine @28" on 3"stand - 107CFM

Plate#2 [not 0ne of Bruces]

On SF110 @6", on 3" Stand [in 1994] 52%/105 - 54.6cfm
On Mine, today - 55.8 CFM

Can't move it around - too small - would open edge of bore up.

So, end result is the plate flows pretty near it's rated value n the test stand. The bore raises the discharge coefficient slightly.

If flowed less in my memory because I had forgotten we tested at 10" on the SF. It can't pull 28... DUH!



Edited By larrycavan on 1246484512

[49-1183904562]

Keith,

This is sounding like and issue with your Pitot tube, Is it and Averaging tube? or single pressure pickup in the cnter of your pipe?. if so turbulence can rase H#ll on a single pickup.

Rick

[slracer]

Keith, slip a thread through a length of small tubing and move the end to different spots on the plate and into different places in the opening. Change the length of the string and do it again a couple more times. Watch the loose end of the string. It will certainly tell you how bad a turbulence problem you might have and also if your flow is going only in one direction. This might help answer some questions. As Bruce would say "Engineers, always want MORE DATA!"

Doug

[jfholm]

And you can tell when an engineer is retired as they don't get out of bed to post on the forum until 9 am :;):

John

[slracer]

John, Who gets up at 11:32 AM?

[jfholm]

:D I am at work and have to sneak in to comment between tech calls - that's my excuse and I'm sticking to it

[K-Star Automotive]

front side with out head

[K-Star Automotive]

Front side with head