suggestions for orifice sizes

[laser3kw]

I currently own a Superflow 110 and now I am building a larger bench. I plan on using a FP1 as the electronics but I am contemplating using three or four orifices to improve resolution.
The prime air mover will be bi-directional (meaning one source point for pressure and vacuum)and rpm controllable. It will also have a depression control via bypass valve between the supply side (conduit going to the test plenum) and the discharge/intake of the air mover. I am aiming for a target of 800cfm, but I think it will hit 1000+ if I over speed the motor (variable speed inverter).
Here is where some thought is required. My resolution needs are literally from 5cfm to max 800+. Not all at one time, but one project with a .750" carb bore or 1" inlet valve will require the low range and a automotive head with a 2" inlet valve my need a intermediate range and then some unknown project may need all 800 cfm.
So here is what I am proposing: conduit #1 will have a 1" orifice, conduit #2 will have a 2" orifice and conduit #3 will have a 3.75 orifice. The conduits, which are fed by the test plenum, will have a flap shutter, operated by electric solenoid, . The orifice will be down stream mid point in a straight lenght of conduit. The pressure taps for the FP1 on each conduit will be isolated so that when not in use, they will not supply signal to the FP1.
My intent is, by using a smaller orifice, I can generate a better suited signal for the FP1. I don't think a single 3.75" will have a dependable signal below 100 cfm (as an example). By using individual conduits, I will eliminate and sealing issues generated by a rotating disc with orifices in it. I also plan some other electronic switching and function controls to facilitate overall functions and may interface it to motor controll and possible the FP1 software.
So, after all that explanation, does this arrangement look plausable? Three orifice to cover the ranges? Or will I need more? I sure hope not!

[bruce]

When you say "conduit" are you refering to a peice of pipe? If so, as discussed here in previous posts an orifice inside a pipe is going to have a different Cd.

If you are using pipe for your conduit why not just go pitot style? Flow elements can be made for each flow range you want then all you have to do is tell the FP1 which flow element you are using. I have a 1.5", 2" and 3" flow element madeup for my bench and I just swap them in and out as needed for various flow ranges. Mostly I use the 1.5" since my main testing is on parts smaller than 1.5" dia.

[laser3kw]

Thank you Bruce for reponding. I tried to research as much as possible on this site, but I know I missed stuff like this. I will check that out.
"Conduit" meaning a piece of pipe? Well yes and no. The small and intermediate orifice would possibly be in maybe 4" or a 6" pvc pipe and the 3.75 would be in a box plenum. I vaguely understand about the Cd and know that an orifice needs a flow field, perpendicular to the orifices flow axis. How much area ratio is needed, I don't know.
I have considered the pitot style, but here again, A)I do not know enough about them, - I understand the principle, but I have concerns about a single element in the middle of a pipe as far as consistant signal as the flow turbulance buffets past it. Multiple element makes since, But I do not know how to build or implement one. B) my finances dictate that I build as much as I can. I have priced some ready made stuff, but I can't justify spending $200 for one size( that may not have be stable at extermly low flow rates) and $350 for another (and I understood that it may not be bi-directional or intended for use as bi-directional). So that means I would have to buy or build a pitot for the smaller range. I know some members out there have experiance with pitots.
On the other hand, I can wire EDM any orfice size I need, +/-.0005 or better in size and roundness. I can also build a plenum box to house the largest, and I hope our discussion will confirm wether I can mount the 1" and 2" in a pipe of some diameter. If not I can incorporate phenums for those also maybe with some perf screen baffles to help settle the flow.
I also plan on having all ranges mounted and accessible for reliablity and convinance.
I appreiate any and all input to this project. If I sound resistant to an idea, It's because I don't understand it, and need convincing and some education. That's why I am here, because of the knowlegde base and the people.

[larrycavan]

You really need to pick one design or the other. A hybrid won't get a lot of direct support with solid answers. It may get a lot of assistance from some forum members but they'll be fishing for answers as much as the builder I'll wager...

Go Pitot or Go Orifice....don't mix them up by putting an orifice in a pipe or you'll sorting it out mostly by yourself...

JMO

[Thomas Vaught]

While I like the "stopper plate" type bench, a famous head porter named C.J. Batten used to have several flow benches that were built with a suction source (Belt driven Paxton supercharger), three Flow Tubes based off of a common 4" PVC pipe diameter system, and Merrium manometers.

One flow tube was 4" in diameter with a 300 cfm orifice.
One flow tube was a 3" pipe with a 200 cfm orifice.
The last flow tube was a 2" pipe with a 100 cfm orifice.

The manometers were 8" delta P so the calcs in 86Rocco's
spreadsheet would have to be adjusted to that value.

The tubes could be swapped by loosening two rubber hose clamps and removing the tube from the system and installing a new one.

Not saying that it will not work but the benches were about 8 feet long!

They used a 55 gallon steel drum for the settling chamber.

Tom V.

[laser3kw]

Thanks to Larry and Thomas for the help.
To answer Larry - I tried to answer Bruce why I have not considered a pitot style. I am not considering a hybrid - I can't imagine that can of worms! I would consider a pitot style thru out if I knew how to fabricat all the neccessary parts.

I am perferring and pursueing the orifice style because of the simplicity to build. I understand now about trying to use an orifice inside a conduit.
My approach will be a three chamber/plenum design. Each orifice chamber will be fed from the test plenum and each will have a shutter to block when not in use(only one orifice will supply readings at a time - no multiples like the blue box). Each orifice chamber will be common at the prime air mover. Each orifice chamber will have the orifice mounted in the center. Shoud I use perferated screen as a baffle/defuser on both sides of each orifice? How far from the orifice should they be mounted?
As far as the prime air mover, it should supply pressure or vacuum to 800cfm at 28" water. I also will be relying heavily on the FP1 to provide the accuracy and resolution range. That's why I have parred the system down to only three orifices. Tentatively, I plan on a 1.500"(170cfm), a 2.500"(475cfm) an a 3.750" (1000cfm). I hope the FP1 will pick up low enough to have substantial crossover i.e.the 2.500" will have stable readings at 100cfm flow and the 3.75 will have stable readings at 350cfm flows.
So the basic premiss of the system will be:
mount part on test plenum
turn select switch to planned test range - that will open the correct flap door to the orifice chamber and it will enable the ps2 port to that orifice and disable the others.
Select intake or exhaust - that will set the direction of the air mover and select the "polarity" of the ps2 port connections.
Trim the test pressure via bypass(intake to exhaust) on the airmover and by motor speed.
read out on FP1.

What do you think? pluasable? on track? way off?

[larrycavan]