Fabricating velocity probes

[slracer]

Thanks Rick, We still have to see what happens in a real port. I would expect the flow to be very well behaved in a straight, circular port so there would be little chance for variation with position (except near the walls, but that also holds true for a standard probe with multiple static holes).

When I saw the shelf in John's shop, I was wondering how he got into mine for pics without me knowing! :p

Thanks for all the work John! Looking forward to the rest of the test. Not too sure I would have said that last week!

Doug

[johno]

Is it possible to hook-up pitot velocity probes to a vertical or inclined manometer and get correct pressure readings (which you then convert to a velocity figure)? ???

[86rocco1]

Absolutely! That's sort of the whole point of the exercise.

[49-1183904562]

Johno,

The PTS Digital Monometer does that and puts it right up on the screen...

Rick

Sorry guy's just a good oportunity to push Bruces DM

[msj442]

and yes might i add it is really awesome feature. i have baffled some customers with it.

max

[johno]

Oh no, i'm not buying any more American powered (120volt) electrical equipment again!! I discovered the hard way when i purchased my Flow-Quick! Bloody things are useless over here in oz with-out a power transformer!! So which fluid manometer (vert/inclined) do you hook-up velocity probes too?

[86rocco1]

Bruce has taken that into consideration, the PTS DM uses a DC power supply which you should easily be able source locally. If that's all that's stopping you, ask Bruce for the specs.

[coulterracn]

[johno]

Thanks for the info. mate! Im using a 'U' shaped manometer, do you have to hook-up both ends of the manometer to the two ports of the velocity probe to get correct readings? :;):

[86rocco1]

[49-1183904562]

Johno,

If you are stuck on fluid than yes you hook it across both sides of the monometer. The static port goes to the side of the utube you want to rise and the Pito/impact side goes to the side you want to fall (push the fluid down).

Also i would do a chart giving you a quick ref of Inch H20 to FPS so as you probe you are not stopping to do calculations.

JMO

Rick



Edited By 1960FL on 1250022101

[Tony]

[stef-1]

I like the way that slracer has made that probe. I have some small bore brass pipe that I may play around with and try to make something similar.
Also I'm pretty sure I've seen a similar looking probe used before, in an SAE paper. I'll have a look tonight to see if can dig out the paper.

[jfholm]

I have finished testing Doug's (slracer) velocity probes. I made me a fixture that would hold the probes in fixed position and I would not have to worry about my hand wiggling around. This way I could be sure of the results and have it be repeatable.

What I did was put a small dot on my port wall on the push rod curve about 3/4" in where the velocity would be the fastest. I aligned the pressure tip up with this dot .030" off the wall every time but would rotate the main tube with the static ports up horizontal and down. I repeated this test twice for validity. Below are the results:

Test 1
#1 - main tube up = 197.1 fps
#2 - main tube horizontal = 183.2 fps
#3 - main tube down = 175.4 fps

Test 2
#1 - main tube up = 197.5 fps
#2 - main tube horizontal = 181.6 fps
#3 - main tub e down = 175.1 fps

I feel the reason this is happening is that the static ports rotate around into a different stream of air.

I then flowed my conventional velocity probe where the static ports are behind the pressure tip on the same tube and are aligned with each other. Just look at the difference in variation don't compare these fps readings with Doug's as I bumped the speed controller and had knocked the test pressure higher. btw when I flowed with Doug's I was at a 10" H2O test pressure.

My conventional velocity probe:

#1 - main tube up = 212 fps
#2 - main tube horizontal = 213 fps
#3 - main tube down = 214 fps

My conclusion is that the static ports need to be on the same tube and in align with the pressure port in the tip so that you get a repeatable measurement.

btw Doug's velocity probe's are of an extremely high quality construction so I feel that the results are legitimate.

John

[86rocco1]

Those results are sort of what I was expecting to see and that's too bad, I was really hoping it'd work better. That idea would have been an elegant solution to building probes for tight spaces.