Fabricating velocity probes

[SuperRunner]

Ok, got my pitot tube done. This is my 4th one, the first 3 failed when I tried to bend. I don't know if the brass is a lower quality, because I was able to bend the 1/8 sample pieces the bender came with, but then when I tried to bend my brass tube that I got from mcmaster, it would snap. I had to heat it up before I could bend it. I still want to make another as I made my bend the wrong direction, plus I want to have one that is at least 12-15 inches.

Now, I assume that each side of the pitot tube goes to each respective side of the inclined manometer. Nothing vents to the atmosphere?

[bruce]

Nothing vents to atmoshere since you are reading the differential pressure between static and impact pressure.

You do have 2 seperate circuits in your probe? I can't tell where you drilled your static holes?

[bruce]

[Jesse Lackman]

[SuperRunner]

[bruce]

If you are using a water manometer for your testing you need to use a correction factor for temp and baro. This would put all your numbers from one day to the next at a standard.

You have to also make sure you are testing at the same static depression everytime. I personally would not rely on a correction to a standard static pressure.

[SuperRunner]

darn I was going to use water because my scale is only 36 inches. I have some dywer fluid, but I won't get 36 and I know I will need that. Guess I need to get a longer measuring stick so I can use the oil instead.

[86rocco]

[Jesse Lackman]

Well I wonder how much difference a weather change makes on a pitot flow bench. The weather change affects only one thing, the air flow reading. On a dyno it can have a "crack the whip" effect as the weather change affects much more the the air flow, the weather change can be "compounded" through the engine. So by the time you get to the CHP and CTQ numbers there is a major difference between brake and corrected. There is probably much less change on a flow bench between scfm and acfm.

[bruce]

[86rocco]

[bruce]

Please define "weather" ?

[86rocco]

For the purposes of this discussion, anything that has an effect on air density primarily temperature and barometric pressure.

[cspeier]

So rocco let me get this straight. Your saying that temp and bar pressure effect your velocity readings? I don't buy it. If that were the case, your head would flow different each time due to the same factors, I've never seen that on my orifice style bench. The basic rule of thumb is the velocity reading shouldn't be any higher than the depression your checking with.

I've been playing with the same head for a year. Cold winter days, 100 degree summer days. The cfm and velocity are the same every time! No correction, nothing! The veloicty reading is a direct reflection of the port size.

[86rocco]