Fabricating velocity probes

[86rocco]

I'd like to fabricate a couple pitot tube velocity probes like these sold by Audietech but I'm uncertian as to the design criteria, is it as simple as one tube inside another with one end of one tube exposed to the air flow and static ports in the side of the other?

[Mouse]

[Zane Bates]

I have spent alot of time reading ,but I am still missing some stuff so bear with me.
Is there a way to measure the info the Pitot tubes will present without purchasing a controller.

[bruce]

A simple setup I use is a thin peice of stainless steel tubing (micro-tubing) attached to a vertical water manometer. As you probe the port the water column changes. Higher readings indicate fast air and lower readings indicate slower air. It does not read impact pressure and is only one tube.

This is going to be something that you have to say "hey what do I actually want to know" Do I want to just see what is going on or do you want actual numbers in velocity? If you want the latter get out your wallet and purchase the Professionally made wands. Making them yourself? Drilling those little holes will be a murder!! I know how hard it is to do it on brass I can only imagine what it would be like on stainless?

[86rocco]

I'm not so much interested in hard, accurate velocity numbers but I would like a good measure of repeatability so that I can do before and after testing with a certain degree of confidence.

However I do like the simplicity of your qualitative approach, I'll consider it a back up plan in case the pitot tubes don't work out. I was planning to make them out of brass tube 1/8 and 1/16" OD

BTW, Zane, you don't need a a controller, a manometer of any type will do provided it reads in the appropriate range.

[Mouse]

This setup uses just a piece of tubing to measure impact or static pressure. Bending a piece of 1/16" tubing you can pinpoint probe some very tight areas measuring static pressure. You can amplify the readings by using a multiplication factor. For instance, you can multiply the readings by 1000 or so for some very slow areas.

[bruce]

I have various probes in tubing diameters of .031, .062 and .125, the smaller dia ones show turbulence quite well as they "flail in the wind". The .031 one will follow along the surface of a port and conform to it quite nice. Make sure if you use a vertical manometer you make it extremely long so you do not suck all the water out of it! Getting close to the seats will have a serious effect on that I have found.

Also get ready for information overload when you start mapping ports, it will generate alot of info and you have to figureout just what it all means. My testing to date has just been in gross gains in CFM's which I have been quite happy with finding, if you recall my testing is done mostly on flatheads and its a whole nother can of worms with them . . .

[Zane Bates]

I guess it was simpler than I thought.LOL
What is involved in having one that measures the velocity and will show the pressure in the Pitot tube also.
It is real important for the pressure in the Pitot tube not to mirror your bench depression.It must be less.

If I need to by a prebuilt unit to do this what is the best Value.

[86rocco]

I just made a prototype, 14" overall length, 1/8" OD with 2-1mm static ports. Any comments?

[bruce]

Looks good, did you try it out yet?

[86rocco]

I did a quick check using a vacuum cleaner for air flow, it seem to work pretty good, well enough to know I'm going to need to build a bigger manometer or buy a digital one, Mouse's system looks pretty slick, at some point in time, it'd be nice to have a system like that, but first, I need to devise a more rigorous testing procedure to see if the probe will give me meanful, repeatable results.

[Christian]

Made myself also a flowprobe about .106" OD and .05 Diameter of innertube, it looks just ridiculously small, how is your tube working, repeatable, results? Unfortunately i didnt have the time yet to check mine for function, just looks so small, hmm maybe im just to skeptical.

[86rocco]

I haven't had a chance to do any rigorous testing yet, initial results look promising. Right now, I'm not very well set up to do the type of testing that's so I've asking Bruce to help me out with that, I've since made a second probe and the first probe, the one in the picture, is enroute to Bruce right now.

[Christian]

[color=#000000]Hey sounds good, tried mine yesterday in the kitchensin..

[86rocco]

I've just received some positive feedback from Bruce regarding the performance of my first prototype so I thought I post up a picture of my second one. It's 4" longer, the radius at the end is a bit tighter and I've also refined my construction techniques a bit.