Velocity Profile work - What am I missing?

[MMack]

After nearly a year, I finally got my J-bend Pitot tube hooked up and tried to use it. I have a head I have been struggling over for a head for a few weeks. I just set everything up, but I am getting just like 2-3" of depression across the two sides of the pitot tube. I know that I am doing something wrong, but I don't know what. Any help you can offer would be greatly appreciated.

Thanks,
Mike

[blaktopr]

Who's tube is it Mike? Homebuilt or bought? All the connections tight? May take some time for the depression to come up depending on the unit.

Chris.

[bruce]

I somehow missed this post the other day, if it's one of mine they are tested here in the shop before leaving. I set every one up in a test fixture on my bench to make sure it meets a simple standard I use to verify accuracy.

If it's one of mine and you can't get it worked out let me know and I'll send out a replacement.

[MMack]

This is one of your pitot tubes. I am porting a Nissan OHC head for a kid who drag races. I am showing about 160-170 cfm, which should give about 230 ft/s average. With the Manometer vertical, I get about 3-4" max. I put it on an incline to get some resolution, but that is still all I get. If I leave it in one place, I don't see a difference. It is stable. When I blow on the static port, it is easy to blow. If I blow on the velocity fitting, there is a lot more pressure. It does seem to be indicative of where the issues are, but I am not getting the DP that I would expect. I was expecting them to be in the 7-9" range. Is that correct?

Mike

[bruce]

Testing at 28" static?

[jfholm]

Bruce,
Brings up a very good point. I only test at 10" H2O right now. That only gives me in the 4" - 7" range most of the time on my pitot and then you have to convert to 28" reading. There is a spread sheet on this forum to do that.

This is probably a good call on Bruce's part.

John

[slracer]

I have been reading this thread and it struck me that you "orifice" types have to "revert" to pitots to do velocity profiles. That brings with it all the attendant pressure and temperature corrections that we "pitoters" do when we flow, and you also can't use your "ratiometric" scales. While we are here, do you use a vertical manometer or an inclined when doing profiles? I know the PTS DM uses a separate sensor, but what about those "water" gauges? For that matter, what does FloSoft and the DM record? Thanks, Doug

[jfholm]

I use a vertical manometer and electronic both

John

[slracer]

John, You didn't say if you do the corrections required for temperature and pressure when you do a velocity profile? I'm not even sure how you do it. Anyone want to explain?

Doug

[MMack]

I am testing at 28". I am not doing any correction factors, but looking at the equations, I didn't see that they would make that much of a difference. I am too far away from what I think I should be seeing.

Mike

[slracer]

Mike, Where are the equations you are looking at? I downloaded a velocity converter from here but can't find the source now. It was appended "Adapted from Larry Cavanaugh's spreadsheet: 'Pitot Velocity Calculations Helper'. There are obviously large changes due to test pressure, but no input for atmospheric corrections.

I found Larry's original file here:



but no equations. I guess it's the engineer in me that wants to see them. -- Doug

[bruce]

Ok a little trouble shooting. Find a piece of 1" PVC pipe a foot or two long, adapt that to your bench and stick the probe in and let me know what your reading is at ~28"? I want to verify the probe is working correctly.

edit: 1" PVC was 2"



Edited By bruce on 1236797021

[MMack]

OK, haven't had time to make the pvc pipe deal, I lunched the engine in my daily driver, a '90 civic Si that I bought to save gas. Wife is just tickled that the car I bought to save money is going to cost more!!! Oh well.

Back to work.

Finally got the old laptop I am buying from a friend loaded up and operational with the new PTS electronics, Very Cool stuff! I only hooked up the velocity probe for now as I was supposed to be working on a wrecked customer race car and a customer head. With the head flowing at 28", showing 37% on what I think is a 400 cfm home made plate, I get a max reading on the DM of about 145 fps. I will get my new Bruce plate in the box soon and hook up the other sensors to get better info. I'll also try to rig up that 1" PVC.

Mike

[joep]

so if someone sets up a bench for orifice then a "change over" needs to be done to use a velocity probe?
I also plan on buying an electronic set up too for the ease of use, but if it doesnt simplify anything then old school it is?????

[bruce]

This is in the Flowbench DAQ area but I'll add a comment here. The PTS DM comes with 3 sensors already installed, no upgrades required or changing connections etc. They are PT1 = Depression, PT2 = CFM and PT3 = Velocity (FPS or H2O) with H2O you can use PT3 as a second "vertical manometer" for testing fuel signals or anything else you would like to measure in H2O.

We also installed 2 jacks that will allow future upgrades for other inputs such as a switch for data capture. The second input is under discussion currently with possible uses for a swirl sensor or other voltage input.

This is all Standard in the basic PTS Digital Manometer no sending it back to the factory for upgrades.



Edited By bruce on 1238204382