Short flow elements

[Scott]

I would like to make Averaging Pitot flow elements for my small bench and place them where the orifice would normally go. How do you guys think it would work if I made them say 1-1/4 ID and 8" long, having an ideal inlet radius on the incoming side? These will not be in any pipe runs, just open on each end. When working on the exhaust side I would use a plug to cover the intake element and vice versa. Thoughts welcome.

RRBD

[2seater]

Since no one else has ventured a comment, I would think the theory should work, although the length you suggest sounds too short. The only way to know for sure would be to test your theory. Avoiding turbulence at the actual measuring pitots is required, and it may be possible to make the tube shorter than the general recommendation of ten diameters upstream and five diameters downstream. The shorter you can make the flow tube, while keeping the accuracy, the more efficient it will be at flowing air through less friction loss. The bench I made is also very minimal in design, essentially just a piece of countertop bolted to the wall, with a settling chamber made from a stainless steel pot under the test opening, a toilet flange bolted to the bottom of the bowl, a short piece of 4" pvc with a homemade flow damper to control gross depression and a single 4" x 3" elbow. The actual motor box is mounted on wheels, contains six vacuum motors mounted to a plate that can be flipped over for vacuum or pressure testing. There is a single toilet flange on the motor box and the motor box connects straight to the elbow under the bench with rubber Fernco couplings or reducers with the selected flow element in between.

[Scott]

Okay, no replies? See the greater the Cd, the more obtainable flow from the bench and thats what I'm after. I had a better thought, I'll post it on the other side.
(thanks 2seater, you must of posted while I was typing)
RRBD

[bruce]

[Scott]

I felt as though the inlet radius (R=.5d) would help as far as smoothing out the velocity profile coming into the element. I thought that way about the inlet radius creating a sort of velocity stack effect, but have also thought that the averaging pitot doesnt know the difference, and wouldnt an increase in velocity also increase static pressure? I really dont know, what is "right" I think that the run is also extremely short, and picked that length due to space considerations. You, John & Tom V. have way more knowledge than me on these things. Is a Cd of 1.0 as good as you can get or can it be greater? It seems the whole flowbench industry has rested on SE Orifice's and Pitot's. Pitot's are great, they're more efficient from a motor standpoint, but arent as user friendly when it comes to swapping ranges and SE Orifices need alot of motor to get into the higher depression and big CFM. I'm just exploring other avenues. I think I will explore the nozzle avenue for my application, but would like to continue this thread with everyones thoughts for educational puposes(mostly mine)

As far as static ports go, on my little Pitot bench I posted pics of, I used a parting tool to cut a groove in the PVC and then drilled .040 dia holes 60 degrees apart in the groove and then glued a sleeve over it with a single 5/32" tube that aligned with the groove. This gave me a very good average static readng. The averaging Pitot was per duct traversing std. I was planning on making these the same way, before switching to the nozzle idea.

As far as Inlet radi', I've tested a shitload of radi'(no cones, using only 180 degree full radius sweep) and found that T.o.o's formula is really close to as good as it gets.

RRBD

[bruce]

It is worth exploring and I might just do some testing of my own when I get a chance to make up some parts. I have plenty of PVC round here in the shop to play with and its easy to machine, if you screw up you just glue another peice on and remachine it!

I've been using PVC to machine up velocity stacks for my carb testing and it has been interesting what 1* of change can do . . .

[Mouse]

Scott, where are the pics of your bench located?

John

[Scott]

"Easy pitot bench" is the name of the post, just a couple below this one.

I wanted to do the short flow elements for the little orifice bench I built, the pics of that are in the orifice area, but I've changed my mind an am going to try a radius'd orifice, its in the machine as I type, I'll post pics of it on the other side when I'm done.

RRBD

[riga team]

Somebody can tried the truncated measure of tools, less 4D from STRAITENER down to pitot?;; touch elements of management МАF in the engine have 1D from a grid down to an element... It well should lay on a place of their average of the tool of a measure pitot and easily varies on 180 to have two directions concerning the basic pipe, also this good to be located there ellipse PITOT... Also in greater pipes D PITOT close to a grid... Where rules? Anatolij