How does a pitot tube bench work? - ??

[Greg]

OK,
After looking at Bruces bench photos I like the look of what I see but dont quite understand how it works.

Does anyone have schematics/photos/drawings of everything involved and a description of how they work?

Is there a need for different sized pipes for different flow rates?

What are these type of bench like compared to an orifice plate bench for accuracy and repeatability?

I've probably got a thousand other questions but this will do for now.

Bruce, how much for the parts you are selling plus some plans etc? Your work looks very good.

Greg.

[98-1074649673]

Thanks for the positive comments on my bench! Just goes to show what can be done in the homeshop with limited funds. The bench u see in my pics is the bench I am using currently, I'm working on a new bigger bench which should be done sometime (?). I can configure the bench I am using to help troubleshoot problems others might be having with their setups.

My bench is accurate and will flow the numbers with the commercial benches being sold, I know I've had parts flowed on both. Repeatability is what u are after not comparing numbers if your bench flows the same from day to day thats what u want.

My intent is not to sell plans, everything u need to know is on this website either in the old archives or here in the "brain trust" of the forum for you to build a bench without plans. I would not feel right selling plans nor would I feel right if anyone who came to this forum and took info from here did the same thing. I sell parts to assist you in making a flowbench since I have the equipment to do that and saves someone the expense (my cost is far cheaper than another machineshop would make them for). Prices can be found on my flowbench parts link.

Again, let me remind everyone I'm not here to make money off this info, I feel this info belongs in the public domain and thats why I sponsor the forum. But if u want to upgrade to better parts and computer sensors then u need to pay for this knowledge

I guess I should take the time to make a simple set of plans that explains it easier . . . I'll look into this in the near future. Till that time enjoy the valuable info found here for free!!

In answer to your question about different flowtubes for different ranges I would answer yes I have a 3", 2" and 1.5" depending on what I am flowing. Don't ask me which one is for what range though most of my work is 1"-2" diameters valves and carbs, I haven't gotten into bigger items yet

[Mouse]

Greg,

Everything you need to know about pitot tubes can be found on the internet. Do searches for "Pitot tube" and "Annubar". Keep doing searches from day to day as web pages get dropped and picked up by search engines daily.

In a nut shell, Annubars can be accurate to 1%.

They are classified as a "differential producer" as too are orifices.

I tend to believe that flow numbers will not be the same (but similar) as an orifice, because the air is treated and measured in different ways.

While the air is squeezed through an orifice and the pressure on each side of the orifice is measured and compared on an orifice bench, a pitot tube does not squeeze the air through a tight hole, but rather simply samples the velocity at several points in the air pathway (the tube open end or little holes drilled in the tube, are aimed into the air flow, like little air scoops) and compares the velocity pressure to the static pressure, which is measured at the wall of the air pathway or behind the pitot tube.

When you measure air volume with a an Annubar (a pitot tube with several sampling ports, or holes) you are measuring the average velocity, and thus, the average air volume flow.

John