PTS Flowbench Forum

I was having issues with my pitot tube so I decided to do a comparison against a PT Dwyer. I felt the proper way to confirm what I was seeing was with a water manometer..

I did just that. All a Performance Trends does is modify a Dwyer. My PTS reads 22" on the manometer and 315fps on the electronics. The PT Dwyer reads 17" and 275fps on the electronics.

The area is 2.89in and is moving 370 cfm.

370x2.4= 888 / 315 = 2.82in
370x2.4= 888 / 275 = 3.23in

I say the PTS is totally accurate. I say the PT Dwyer might be inaccurate..

What does anyone else say??

Were they both in the exact same position in your testing part?

I test all my probes in a test fixture on my flowbench after they are finished. I can see a difference of ~25 fps depending on the tips orientation in my fixture.

Brucepts wrote:Were they both in the exact same position in your testing part?

I test all my probes in a test fixture on my flowbench after they are finished. I can see a difference of ~25 fps depending on the tips orientation in my fixture.

Bruce has just pointed out a very important aspect of testing with a probe. It is next to impossible to hold the probe by hand and get really good repeatable tests. I made a holder to actually hold by probe in place and not move around. My prototype is kind of ugly, but I am working on a nice one made from aluminum.

John

here is a tube I built to calibrate my settings for my probes - by the way the entrance to the tube is radiused

jfholm wrote"

here is a tube I built to calibrate my settings for my probes

John could you tell me or us what the total height is with your Tube to calibrate the setting for velocity probes & is the tube OD size 2" or 1.500

Thanks in advance

Malvin wrote:

jfholm wrote"

here is a tube I built to calibrate my settings for my probes

John could you tell me or us what the total height is with your Tube to calibrate the setting for velocity probes & is the tube OD size 2" or 1.500

Thanks in advance

Malvin,
The tube is the black plastic tubing you can get at HomeDepot for drains (waste water). It is 1.5" i.d. the bottom vertical tube is just 6 inches long and the top horizontal tube is 10 inches long. When I calibrate my probe I use my holder so it is steady and put it about half way down the top tube right in the center of the diameter. Then I run it up to what ever test pressure I want to calibrate to and take a reading. I am using one of the programs that I got from this forum that tells what velocity a certain diameter should give at a certain test pressure and cfm. Your probe should be close then. btw do not assume the id is exactly 1.5". I used my inside snap gauges and I think I found it to be 1.6" in reality. I have attached the spreadsheet to calculate the velocity probe.
btw I did not do this spread sheet. I think Ed did but I can't remember. Whoever did it stand up and take a well deserved round of applause, thank you!

John

Personally, the same location is of no concern to me in seeing if the probes match. The fastest speed, is the fastest speed, period. I find those areas in my testing.

This is why I lay my probe on the floor instead of off. I have enough data to know what's going on now. It's a PIA to "try" and keep it off the floor. I don't even try..

jfholm wrote: btw I did not do this spread sheet. I think Ed did but I can't remember. Whoever did it stand up and take a well deserved round of applause, thank you!

John

That's mine, sort of anyways, it's a fragment of one of my bigger spreadsheets someone's pulled out just the Pitot tube section.

And you're welcome, I'm happy to have made a contribution.

John, Those pics have an "interesting" pitot probe laying on the bench! -- Doug

Yes Doug, that is when I was testing them compared to my standard. That was right before the "flood" I need to get it set back up and try again so I can send them back to you. I think my schedule has been as bad as yours. I guess we should pick up where we left off You need to get your cattle prode out and stick firmly on my butt.