PTS Flowbench Forum

So I have a question.

Rocco's spreadsheet does not seem to have an input for pressure or Vacuum when calculating flow of the plate.

I was always under the impression the CD would be different for these two operations. I have seen some posts on here and the old forum discussing this too but I can't seem to find what adjustment to make. I have searched quite a bit so I appologize if this is a re-hash of an old topic that I somehow missed.

Thanks for any input,

Chris

ccm399 wrote:So I have a question.

Rocco's spreadsheet does not seem to have an input for pressure or Vacuum when calculating flow of the plate.

I was always under the impression the CD would be different for these two operations. I have seen some posts on here and the old forum discussing this too but I can't seem to find what adjustment to make. I have searched quite a bit so I appologize if this is a re-hash of an old topic that I somehow missed.

Thanks for any input,

Chris

Chris,
What I think you are referring to is the way the internal orifice acts when in exhaust (blow) mode compared to intake (suck) mode. There was some discussion about what happens when the internal orifice approaches the size of the hole in the panel it is mounted on between the two chambers. This really was apparent on the 12 motor benches. When in blow mode and you had a large internal orifice the bench would act like an orifice in a tube a little as the wood the orifice is mounted on is 3/4" thick. I think Bruce is working on an orifice mounting device so you would have a larger flat area on both sides of the orifice to remedy this problem. I have one in my bench that I built.

Now one other thing, if you have the orifices from Bruce that have a 45º taper on one side of the plate you have to turn those over when blowing as compared to sucking. I have Bruce's orifices for my bench and they are very high quality. You could then use Ed's spreadsheet as it would be relevant no matter which direction you are flowing.

If not just calibrate your bench for suck and then for blow. Adjust the CD so the orifice reads the same either direction. As example on intake your orifice may have a CD of .597 and exhaust a CD of .602 or visa versa. You would just adjust the CD so the orifice reads the same either direction and do this for all of your internal orifices.

John

Thanks John,

Wait 'til you see what I have cooked up for my orifice mount. I think you'll like it!

I have a couple Merium Instruments orifice plates I may be able to use for calibration. I have the actual flow chart for each plate in "Intake Mode" and "Exhaust Mode". We'll see.

Stay tuned.

Chris

ccm399 wrote:Thanks John,

Wait 'til you see what I have cooked up for my orifice mount. I think you'll like it!

I have a couple Merium Instruments orifice plates I may be able to use for calibration. I have the actual flow chart for each plate in "Intake Mode" and "Exhaust Mode". We'll see.

Stay tuned.

Chris

Just keep in mind that a lot of times those plates are calibrated for orifice in a tube with the tube of a certain diameter. So make sure you are comparing apples to apples etc

Agreed. These are for sure calibrated for 4" PVC pipe. They may be useless, not sure. Well the flow sheets anyway.

Chris

ccm399 wrote:Agreed. These are for sure calibrated for 4" PVC pipe. They may be useless, not sure. Well the flow sheets anyway.

Chris

The orifices should still be valuable for calibrating your bench. I have a bunch of those orifices I found at a surplus store. Brand new in various sizes. They are .125" thick and around 4 13/16" outside diameter. They orifice opening is beveled 45º until there is a .040" face. Bruce's I bought from him are right sharp at the bevel and they check about .597 CD while the ones I pictured here with the .040" face seem to be around a .605 CD. Inside a PVC tube the CD would be higher and the closer the orifice gets to the inside diameter of the tube the higher the CD gets so conceivably .700 or higher.

This particular one has an orifice diameter of 2.250" so at a CD of .605 and flowed at 28" H2O would give me 354.4 cfm per Ed's sheet.

John

Hey John,

Check out my bench build thread for the orifice design I came up with.

Chris

jfholm wrote:
The orifices should still be valuable for calibrating your bench. I have a bunch of those orifices I found at a surplus store. Brand new in various sizes. They are .125" thick and around 4 13/16" outside diameter. They orifice opening is beveled 45º until there is a .040" face. Bruce's I bought from him are right sharp at the bevel and they check about .597 CD while the ones I pictured here with the .040" face seem to be around a .605 CD. Inside a PVC tube the CD would be higher and the closer the orifice gets to the inside diameter of the tube the higher the CD gets so conceivably .700 or higher.

This particular one has an orifice diameter of 2.250" so at a CD of .605 and flowed at 28" H2O would give me 354.4 cfm per Ed's sheet.

John

I use a 2,6425" orifice that resides inside a 125mm / 4.921" pipe. Out in open space it should flow about 293 cfm/ 10". Inside the pipe my industrial flow program says the factual flow is about 305 cfm. At 28" the difference then should be big. 490,28 cfm vs 510,36 using just hand calcs, but if I run it in the program the actual difference is bigger than that..