orifice plate leaking

[Thomas Vaught]

Larry, explain why you feel the very high orifice delta Ps would be an advantage (using smaller orifice hole sizes vs using lower Delta Ps with larger hole diameters.

The blue company went to the higher Delta P because they already had a 400 cfm bench with the appropriate hole sizes: 25 cfm, 50 cfm, 100 cfm, 200 cfm, 300 cfm, and 400 cfm.

By going to the 1.91 sg fluid they increased the flow range by 50% (they added two additional motors too) with virtually no real cost and had a new bench. The new ranges were 37.5 cfm, 75 cfm, 150 cfm, 300 cfm, 450 cfm, and 600 cfm. This moved the effective delta P to about 13.87"
vs the typical 6" and they could still use the Dwyer 246 inclined manometer. Only deal was the 1.91 fluid is very expensive vs the .826 fluid.

Thanks

Tom V.

[larrycavan]

Tom,

Well.... you pretty much sum up the advantage with your point on how "brand blue" created the 600 from the 300 with minimal design changes.

The initial questions Curtis had were regarding orifice sizes for specific ranges he would like to reach with his new bench.

In his second post he mentioned loosing the inclined and going digital with PT accessories. That puts a bit of a different spin on things with regard to "measurable flow".

Setting aside well ratios and fluid SG so they don't muddy the waters on the concept, let's approach a simple comparison of a standard inclined manometer vs a digital setup like the FP1.

Standard inclined vertical rise sets the measurable Delta P.
Digital expands that significantly.

If you want to work off a high Delta P with a standard inclined manometer, you have to adjust the scale through any of 3 possible ways or you can just make it huge.

1. rise
2. well drop ratio
3. fluid SG

With a digital unit like the FP1, since you have the potential of a 40" measurable Delta P, you have an increased measurable flow potential for any given orifice size without the complexity of manometer scale adjustments...So what does that buy you....quite a bit IMO.

In general, I personally feel that sizing of orifices plays a very large role in the design. From my perspective smaller is better and I say that with consideration to:

Vacuum motor capacity
Potential problems with calibrating very large orifices
Potential problems with the air stream being affected by surrounding obstacles inside the plenum...

So is there an optimum? Are large holes with low Delta P not as good as the opposite?

I think an argument could be made either way by many of the forum members. I favor the higher Delta P with a smaller orifice.

I'm always amazed at the way someone will out of the blue, toss out an idea or a concept that puts a new twist on something....It's one of the coolest things about this place....It always makes me stop and think! Even cooler is how it comes from so many different people..beginners and more experienced user alike....Then again my 4 year old grandson asks me questions that leave me searhing for answers...

Best Regards,
Larry C

[Nick]

Nice discussion, I like it!

Curtis,

To add what Tom said, I have tried opening multiple orifices on my bench, and it works just the same as one hole of equal size. I was a doubter so I made my orifices sized up by 50cfm just in case. The next bench will use less orifices. You can see how I did my orifices in the readers flow bench projects under Nick's bench.

Here is my 2 cents on Delta P. (I'm not an engineer so don't Quote me!!).

If you have a large orifice and a very low Delta P, then I would think the orifice would be more subject to turbulence within the bench. The MSD design would not be very happy under this circumstance.


If you have a very small orifice and a high Delta P, I think you are creating a lot of unnecessary turbulence in the bench. It takes energy to move that air, so before it can go through the test piece (exhaust test) it must be dissipated so as not to effect the accuracy. Could that fast moving air corrupt a pressure tap? Would the pressure be higher the closer you go to the orifice? A 12" pressure difference is a lot less "violent" than a 40" difference.

So I don't think either high or low is better. I think there is a sweet spot. Where is it? I don't have a clue.

Am I out in left feild here, what do you think?


Nick

[larrycavan]

[Thomas Vaught]

The man wants to test at 40" test pressure DP.

We can already assume that going from a orifice DP of 6 inches to 13.85 orifice DP is a non issue as the blue company has been there for years (as far as the hole size vs the increased delta P). We have an increase in orifice DP of 2.3 times with a flow increase of 50% (300 cfm for example is now 450 cfm).

Say we increased the orifice DP to 24" for another 50% flow increase and the new test pressure is now 40 inches DP plus the 24 " Orifice DP for a total motor DP of 64 Inches.

So lets say we had the hole sizes like a sf300 bench with the following flow ranges: 25,50,100,200,300,400.

Our 25 cfm hole becomes 50 cfm at 32 inches DP. Our 100 cfm hole is 200 cfm, 200 cfm hole is 400 cfm, 400 cfm hole is 800 cfm.

We know that we need at least 8 (115923) motors to pull about 600 cfm out of a blue box at 37 amps 220 volts to test at around 13.85 orifice DP.

To test at 600 cfm and say 24 inches of orifice DP across the test piece we would need a motor that would be able to pull at least 64 inches of motor DP at the 115923 rated flow of 123 cfm per motor. Can the 115923 do that? I do not know.
Maybe someone can look up the motor/vacuum DP curves again and post that info.

Seems to me like the motors would be screaming along at 64 motor DP just so you could test at 24 inches orifice dp and 40 inches test piece DP vs using a larger hole and testing at 40 inches (test piece DP) and 6 inches (orifice DP) for a total motor DP of 46 inches.

We already know that the 1234 single stage motors cannot do as well on higher motor DP vs the two stage 115923 motors. By going to the 24 inch orifice DP are you forcing yourself to buy the much higher priced 115923 vacuum motors simply because you did not want to make the hole larger? I do not know.

Tell me what you think.

Tom V.

I know that the spreadsheet says that we only need to have a 24 inch orifice DP to get double the flow but I have never confirmed that is true in MY TESTING.

[larrycavan]

[Thomas Vaught]

Larry,

The SF1020 uses 12 of the 115923 motors to get the 1020 cfm they report.

The Orifice in the 1020 bench is actually a diamond shaped part the uses two "Vs" to create the diamond. One "V" is fixed and the other "V" is movable and controlled by a motor controller.

The motors are controlled by a sensor that will maintain a given test pressure or on the newer bench a requested cfm.

Say you have a test part that flows 150 cfm.

You say I want to test this part at 28" delta P
in the test chamber.

The computer will vary the orifice "diamond" opening along with the motor speed until it sees 28" of test pressure in the upper chamber.

It will then measure the delta P across the diamond and calculate the airflow flowing past the diamond orifice plate based on the difference in the pressures above and below the orifice.

It knows the upper chamber pressure as it is specified and verified. It just needs to measure the lower pressure.

As you restrict the air passing through the test part the sensor will sense the higher test pressure and slow down the motors and if necessary move the orifice diamond to calculate the new air flow.

The idea here is that you can test at any test pressure with a matched orifice diameter for that test pressure.

With the cfm deal the computer knows what settings are necessary to get to a given airflow and it will constantly change the test pressure and orifice diameter until the test piece is flowing 300 cfm.

Hope this helps.

Tom V.

ps You could engineer a similar manual controlled Diamond orifice and only have one "orifice in your bench but you would have to have a computer to go through the calculations to tell you what the calculated number was based on the delta P across the orifice you set and the test pressure. Maybe someone can figure that out on the board too.

[Terry_Zakis]

I have an excel file that I set up a while ago, that shows many of the Ametek motors, with flows vs. vacuum levels. Could be useful for you. I think Bruce posted it here once before, but I wasn't able to find it. If interested, email me, and I'll send you a copy of it.

Best Regards,

Terry T.

[Thomas Vaught]

I sent you a PM Terry.

Tom V.

[larrycavan]

[larrycavan]

Tom,

The 1020 is a significant leap in thought and implementation.

I'd recently been thinking about how to build an orifice that could be varied in size without rotating a disk or removing plugs. I had it pictured as an oval with one part statinary and one part movable. I figured the Cd would be a real bear to sort out on something like that....looks like SF found a method though.

Interesting how they chose a diamond shape. Any thoughts on that?

In order to achieve their claimed 60", it appears SF felt the need to go with the more expensive motors..

I'm wondering now, how much efficiency might be elevated by introducing a proper velocity stack to the intake side of the cheaper motors. I figure if someone was going to take Ed's one way check valve to the next level, they may as well shoot for efficiency improvements as well. Maybe a stack on each motor could be the ticket to higher Delta P readings across the orifice with a cheaper motor...don't know for sure..just fishing with that one....

Nick...you've most assuredly got some input on this...
c'mon....don't go quiet now....


Larry C

[Thomas Vaught]

Larry, the 1234 motors do have a nice radiused entry in the drum surface vs the sharp edge on the 115923 motors.

The diamond deal allows the area change to be consistant as the vs are spread farther apart. Even though the area gets larger as the vs go farther apart it is easily calculated vs an oval.

The Vs are also sandwiched together so the orifice thickness is still pretty small.

Why I like this forum, always a lot of thought taking place with easy exchange of info.

Thanks for the PM. PM did not make the trip though, can you resend?

Tom V.

[bruce]

[Nick]

I'm a bus driver I don't know anything.

But here are my thoughts on the superflow 1020. A square hole would be easier to figure the area of than one that started round and when ecliptic (is that a word?) (oh what Tom said) As for how to move it. I was looking at cnc stuff for my lathe, you could use a stepper motor, or better yet a servo motor with position control to move the plates to make the right size hole that you wanted. But you would still have to have a computer and software to make it all work.

I think even better for the home bench dudes would be a digital read out on the moving plates. You could use an excel program to calculate the orifice area based on position of the plates.

Or maybe even cheaper. Machine some type of stops to open the plates to different positions of know area.

What ever you do, It must be made to open to an exact size, or a know exact size. .010 is about 2cfm on a round orifice, so big errors would not be acceptable.

This setup could get expensive in a hurry, but would solve some flow bench hassles.

I wounder what happens when the computer loses its position for the plates and gets off by .100, So much for accuracy.

I think I am starting to forget why I built this flow bench in the first place. I have already came up with a better design and want to build it. I the Idea was to port heads not build the best bench in the know world......

Oh one more thing. I noticed when your setting depression with "All" the motors on, it is easier to get it right. With say 3 on and 1 off, you have to wait for that one motor to start spinning backwards at a constant speed before the manometers stop moving around. It is easier to over shoot or under shoot your test pressure. My point here is check valves would be useful to stop this. I think I may build something this weekend and test it. Something else to build... Right after I build my valve opening fixture and my..............................



Nick

[larrycavan]

Tom,

Are the corners on the diamond pointed or radiused?

A mechanical / manual adjuster setup could work like Nick suggests. It would have to be very precise.

Do you happen to know if the flow rates were the same in both directions on that machine?

Larry C