PTS Flowbench Forum

I've been doing some more thinking about trying an predict what motor dep I can run in the lower chamber as a figure that I can use to work out new different orifice diameters.

In theory if you have enough orifices you only need to run 30" in the lower - 28" + 2"(orifice) = 30", if you have a ton of plates -

Looking at the Ametek that equates to 100cfm per motor.
http://www.alliedelec.com/Images/Produc ... 259287.pdf

I was thinking about looking at motor graphs but now I'm thinking about actual testing.

I had 32.5" dep flowing 324.5 cfm with a 2.54" orifice, and using the Flowbench Calculation spreadsheet it works out that 2.54" with cd 0.62 flows around 325cfm at 14".
So looking at the numbers it looks like 14 + 32.5 = 46.5", where the motors stall out.

What do you think, does this sound like legitimate thinking?

Orifice pressure for the PTS DM was selected simply by available sensor pressures on the market that fit the design. Choice was 8.5", 16" and 40"

8.5" was less stable and creates a large orifice hole at 600cfm, 40" was to much depression we felt, 16" seemed to work out fine with good hole sizes in the 6" square aluminum plate. We did not do any scientific studies I built a DM using each sensor, tested them out and we discussed the findings and settled on the 16" sensor. A 16" sensor allows you to use the whole sensor range on a given plate, if you use a 40" sensor on a 16" range or 2" as you suggest you are only using a portion of the sensors range.

A 600cfm plate at 16" is 3.326" diameter, a 600cfm plate at 2" is 5.593"

So we end up with good plate ranges which are easy to machine in a 6" square plate, repeatable stable readings we can work with in the DM software. The design has been built with all sorts of motors around the world and has more than enough power for those who are building it for their needs, 3 sheets of MDF some melamine for the slider plate which is the only moving part in the design and some glue and screws you are on your way to a flowbench. Not everyone has a need for 600cfm@28" using less powerful motors might mean you need 6-8 motors to achieve 300, 400 or 500cfm.

This all baffles me this discussion, Yes i do understand flowing items like mufflers and intake manifolds but lets be real 600CFM at 28"! if your looking for solid numbers under 50 CFM when your looking at max flow of 590CFM your over my head and working outside the range of the PTS 8 motor bench.

Here are the DM basics, sensor size in working pressure range, minimum voltage resolution, linearity & A-D conversion in digital output; These things dictate the sensitivity and stability of your CRUD data. From here it is all filtering. Dont get me wrong throw money at the equation and i can build you the ideal DM 6 to 8" sensors and 16 bit A-D resolution and for $1500 to $2000 US you could less power in your Delta P. But then with all this added sensitivity what other design compromises will be moved to the for front.


Rick.

Brucepts wrote: Not everyone has a need for 600cfm@28"

That's right - even 600 is way overkill for nearly everybody -, but think about a flowing a 300cfm head. You can now do it at 38"

Brucepts wrote:A 600cfm plate at 16" is 3.326" diameter, a 600cfm plate at 2" is 5.593"

A 300cfm plate at 16" is 2.35" diameter, a 300cfm plate at 2" is 4.0" - well within everyone capacity -.

Using 38" I'm allowed 7.5" on the orifice with my 46.6 limit, and that equates to 2.85", which gives me some range to overlap orifices.

Brucepts wrote:8.5" was less stable and creates a large orifice hole at 600cfm, 40" was to much depression we felt, 16" seemed to work out fine with good hole sizes in the 6" square aluminum plate. We did not do any scientific studies I built a DM using each sensor, tested them out and we discussed the findings and settled on the 16" sensor. A 16" sensor allows you to use the whole sensor range on a given plate, if you use a 40" sensor on a 16" range or 2" as you suggest you are only using a portion of the sensors range.

Just looking at this sheet on page 3 the graph shows that the sensor is more accurate at 1" than 16", so I don't see any need to change sensor, but I do think more work is needed in getting the orifice more stable sooner.

http://www.datasheets360.com/pdf/6060859169405517462

Just looking at this sheet on page 3 the graph shows that the sensor is more accurate at 1" than 16", so I don't see any need to change sensor, but I do think more work is needed in getting the orifice more stable sooner.

Grey, Are you using a PTS DM I was under the impression you were fighting with an FP1?

There are no issues with the PTS DM and Stability! The phenomenon that Bruce and i have discussed in the past is trying to flow with a single 6XX CFM plate and that the numbers down low 25CFM and less were not as stable as we would like so we DO NOT RECOMMEND running in this manor. As i said in an earlier post the ports i work on are between 250 and 350 CFM on intake and i could do everything rock solid with a 425 internal plate calibrated to within 1 cfm at 100, 200, 300 at 28". and yes i can change lates ans test at 35/36" and keep the same resolution.

When you are sampling 12000 times a minute and your averaging is set to 100 you will flushing the buffer 120 times or every 1/2 a second, if your pressure is fluctuating then you will see numbers move. You are talking every .015" of water is 1 AD resolution, if we drop the DP sensor to 8" then that goes to .0075" twice as sensitive and twice as hard to stabilize. The beauty with the DM is that you can move the averaging to 200 and slow the interface down without effecting accuracy.


Rick

There seams to be diminishing returns with larger orifices

300cfm PAP plate on top

40" FP1 with 6 motors through a 3.33" internal orifice running flat out reads
37.6" flowing 351.1cfm
100" FP1 with 6 motors through a 3.33" internal orifice running flat out reads
37.5" flowing 351.9cfm
100" FP1 with 8 motors through a 3.33" internal orifice running flat out reads
41.6" flowing 370.3cfm
100" FP1 with 8 motors through a 4.044" internal orifice running flat out reads
42.9" flowing 377.5cfm

I tried a bigger orifice on the top with the bench running flat out.
My 100" FP1 is more jumpy than the 40" one, which is understandable, so I set the sampling rate to the slowest #20 for stability

My 2.54" 3mm square edge plate on top

100" FP1 with 8 motors through a 4.044" internal orifice running flat out reads
31" flowing 464.7cfm - about 442@28" -

My 3.33" 3mm square edge plate on top

100" FP1 with 8 motors through a 4.044" internal orifice running flat out reads
15.9" flowing 560cfm - about 744@28" -

1960FL wrote:PS. Have you thought about using some sort of averaging tube for the DP pickups like a 1/8 piece of copper fit it the corner following the perimeter of the box with like a .020 hole every 4 inches?

I'm posting this experiment as a historical record - no one has posted what they found out before - as a time saver so that people can make their own judgment whether they should duplicating the experiment again.

Experiment : Test if an averaging tube can reduce fluctuations in DM readings.

Method : A 6ft 3mm PVC tube with 0.36" holes drilled approximately at 6" intervals and plugged end is placed around the perimeter of the internal orifice board on both ends of the incline DM pressure ports. The 100" FP1 is set to the quick/harsh sample rate of #3 to exaggerate the reading jumpiness of the DM. 300cfm PAP plate on top with 6 motors running flat out through a 4.044" internal orifice.

Results :
0.040" restrictor on end of tube encased in a housing.
cfm is at 28"
39.8 302.2 300.7
39.9 304.1 302.6
39.9 301.7 300.2
39.9 305.5 304.0
40.0 302.6 301.1
40.0 302.1 300.6
40.0 302.0 300.5
40.0 300.7 299.2
40.0 301.0 299.4
39.9 302.9 301.4
39.9 301.8 300.2
39.9 301.3 299.8
40.0 301.5 300.0
40.0 300.7 299.2
40.0 302.8 301.3
39.9 303.1 301.6
39.9 301.8 300.2
40.0 302.0 300.5
40.0 298.2 296.7
40.0 302.4 300.9
39.9 301.9 300.4
40.0 300.0 298.5
40.0 302.7 301.2
40.0 299.3 297.8
40.0 301.5 300.0
40.0 299.2 297.7
39.9 305.0 303.4
39.9 297.0 295.5
39.8 303.3 301.8
39.9 303.5 302.0
39.8 304.0 302.4
39.8 301.4 299.9
39.9 300.8 299.3
39.9 301.0 299.5
39.9 301.5 300.0
39.9 303.2 301.6
39.8 304.2 302.6
39.8 303.8 302.3
39.9 300.6 299.1
39.9 300.7 299.2
39.9 298.2 296.7
39.9 300.9 299.4
40.0 301.6 300.1
39.9 301.6 300.1
39.9 302.0 300.5
40.0 301.3 299.8
39.9 301.0 299.5

cfm is actual
39.9 359.0 357.2
40.0 363.6 361.8
40.1 356.8 355.0
40.0 364.5 362.6
40.1 359.8 358.0
40.0 364.4 362.5
40.1 363.7 361.8
40.2 358.7 356.9
40.1 360.0 358.2
40.2 359.5 357.7
40.2 363.3 361.4
40.1 361.8 360.0
40.1 362.4 360.6
40.1 359.3 357.5
40.0 364.9 363.0
40.0 362.4 360.5
40.1 361.9 360.1
40.1 362.8 361.0
40.1 360.6 358.8
40.0 360.4 358.6
40.0 359.1 357.3
40.0 361.2 359.4
40.0 361.3 359.5
40.0 361.0 359.1
40.0 357.7 355.9
40.0 363.6 361.8
40.0 363.0 361.2
40.0 361.5 359.7
40.0 363.3 361.5
40.1 359.7 357.9
40.1 357.0 355.2
40.1 365.1 363.2
40.1 361.8 360.0
40.0 362.3 360.5
40.0 364.0 362.2
40.1 358.4 356.6
40.1 361.5 359.7
40.0 362.4 360.6
40.1 359.1 357.3
40.0 362.2 360.4
40.0 361.6 359.8
40.0 356.8 355.0
40.0 359.7 357.9
40.0 362.4 360.5
40.0 359.8 358.0
40.1 363.1 361.3
40.1 360.7 358.9
40.0 361.8 360.0
40.0 361.6 359.8
40.1 364.2 362.4
40.1 358.8 357.0
40.1 363.5 361.7
40.1 363.0 361.2
40.0 363.7 361.9
40.0 361.5 359.7
40.0 359.3 357.5

Averaging tube
cfm is at 28"
39.3 305.8 304.3
39.4 305.2 303.7
39.5 304.8 303.3
39.5 301.5 300.0
39.5 302.8 301.3
39.5 302.5 301.0
39.5 303.6 302.1
39.5 305.2 303.7
39.4 304.3 302.8
39.5 303.2 301.6
39.5 298.6 297.1
39.5 302.3 300.8
39.4 303.5 302.0
39.5 304.0 302.5
39.5 302.2 300.7
39.5 302.3 300.8
39.5 303.6 302.1
39.5 301.0 299.5
39.4 309.8 308.3
39.5 303.2 301.7
39.4 303.0 301.5
39.4 306.3 304.8
39.4 304.9 303.4
39.5 303.4 301.8
39.4 303.5 302.0
39.4 300.3 298.8
39.4 304.7 303.1
39.4 301.9 300.4
39.3 301.0 299.4
39.3 303.2 301.7
39.3 301.9 300.4
39.3 305.4 303.8
39.3 304.4 302.9
39.3 301.5 300.0
39.3 302.6 301.1
39.2 305.3 303.7
39.3 304.1 302.6
39.3 305.6 304.1
39.3 304.8 303.2
39.3 303.5 302.0
39.4 300.4 298.9
39.3 301.9 300.4
39.2 304.5 303.0
39.3 302.6 301.1
39.3 303.9 302.4
39.3 300.5 299.0
39.3 302.5 300.9
39.3 305.2 303.7
39.3 300.6 299.0
39.3 301.3 299.7
39.3 301.5 300.0
39.3 302.7 301.2
39.3 303.4 301.9
39.3 301.9 300.4
39.3 303.1 301.5
39.4 304.6 303.0
39.3 305.3 303.7
39.3 302.5 301.0
39.3 304.5 302.9

cfm is actual
39.4 356.8 355.1
39.4 358.6 356.8
39.4 361.1 359.3
39.4 356.7 355.0
39.4 359.4 357.6
39.4 357.9 356.1
39.4 361.1 359.2
39.4 359.0 357.2
39.5 362.0 360.2
39.6 361.0 359.2
39.5 361.7 359.9
39.6 361.2 359.4
39.5 360.3 358.5
39.6 360.8 359.0
39.6 360.5 358.7
39.6 363.0 361.2
39.6 361.1 359.3
39.6 360.8 359.0
39.5 365.1 363.3
39.6 357.3 355.5
39.6 361.3 359.5
39.6 361.0 359.2
39.6 361.4 359.6
39.6 359.5 357.7
39.6 363.1 361.3
39.6 358.9 357.1
39.5 358.9 357.1
39.5 358.7 356.9
39.5 360.5 358.7
39.5 357.1 355.3

0.040" restrictor on end of tube encased in a housing at 28" max to min = 8.5cfm
Averaging tube at 28" max to min = 11.2cfm
Each set of readings had erroneous blips that that accentuated the difference between max and min, so if the highest and lowest was removed it would be 5.9cfm and 5.5cfm.

Conclusion : I can't say I see much difference, which may be due to the small holes being a touch big at 0.036".

very interesting grey , I wonder how it would be with, say, 20 thou holes?

On second thought the hole size might not be that big of a problem. If one hole gets a pulse of high pressure another hole will bleed off that pressure before the sensor sees it, and when you drill soft plastic the hole probably closes up a touch when the drill is removed.

The averaging tube is probably a better idea because it works first time, where as a single hole tube will have to be moved around and tested numerous times - I spent one day doing it -.