Pitot Bench with percent scale.

[Scott]

Over the last two days, I have worked on the small bench I started about a year ago. It works great now. Heres some things I found:

I calculated the area of the flow element minus the area of the "averaging pitot" (averaging pitot tube) and by the calc's it worked out to flow about 99.5 cfm. Next I checked it with (8) different diameter orifices,
1.126
1.246
1.265
1.350
1.360
1.454
1.553
1.645
The percentages on my percent of flow scale were very close to what they should be,but not perfect, so I thought that the Orifice's Cd ware off a little from .62 Cd, so I went through and adjusted the Cd's till the numbers were right on(wrote the new Cd on the orifice) with my percent of flow scale. This seemed kinda cheesey since I cmm'd the orifice diameters and they are made form .125 alum plate with dead sharp corners. Anyway, I picked an Orifice and flowed it, then I adusted my calculation of flow element to 103.5 cfm instead of 99.5 as calculated and now the percent scale is dead nuts on with the calculated numbers of each Orifice at a .62 Cd. In this instance it looks like the averaging pitot tube has only a slight effect in my set up. BTW the flow element dia. is 1.360 ID (averaged with caliper). This little bench is built just like Digs pic, minus the flow straighteners. I'll post a pic if I can figure out how...

RRBD