orifice plate leaking

[Jesse Lackman]

That is pretty cool.

I should clear up my 1 cfm comment, IMO measuring a 1 cfm change at flow testing pressure is different than reading 1 cfm at atmospheric pressure which is what the LFE zealots were talking about. So a LFE bench can measure a burp into the test fixture at atmospheric pressure, I don't see how that is any indication of accuracy at normal flow test pressures.

[cboggs]

Larry,

You explained it so even I could understand, .. thank you.

I'll PM bruce and add a 75 cfm disc, ..

Guys, .. arguing about Pitot VS orifice, .. come one now, ..

Curtis

[bruce]

[Jesse Lackman]

Well that french fry comment got my gander up, kind of like bragging my orifice is bigger than your pitot nah nah nah.

Maybe I should build BOTH into my bench, hmmmmm. That would be very simple.....hmmmm.

[Thomas Vaught]

Curtis,

I looked at the motor files that Terry provided for the Ametek 115923 motors and have the following info:

ASSUMING that you were using the Blue 1.91 sg
fluid in your 246 manometer you would have about 14" H20 depression across the orifice plate. Adding to that the 40 inches of depression you wanted across the test part you get 54" total depression on the motors.

You would need 16 motors to pull that kind of depression with high air flow. .

12 motors at 54 inches total depression would move about 850 cfm which is still more than your requirement of I believe 750 cfm at 40 inches test pressure.

The same 12 motors at 30 inches test pressure with the same 14 inches across the orifice would be 1000 cfm capability or 1000 cfm at 44 inches total depression across the system.

Hope this helps.

Tom V.

[cboggs]

Tom,

If I can pull 600 cfm at 40" across the test peice that would be great, ..

I'll calibrate at 28" standard, ..

then see if I can work out 600 cfm ( DRCE pro stock ) at something greater then 35"

I've got 9 motors, ..

Curtis

[Thomas Vaught]

Quote:

"Pilots Suck, and belong on air planes. Who wants to monkey around with correction factors, every five minutes. What happens when crap gets stuck in you fancy pilot holes. I can wet flow. I can smoke test, I can suck clay in my bench if I want. I can suck my french fries in mine if I want. I can go from 25cfm to 1100cfm with one bench, how many different Tubes do you need to accurately test to 1cfm? How about cost, your flow receptacles are 300 bucks, my orifices cost me $15."

I tried one time to interest a friend into a Laminar bench like Buddy Morrison of the famous Reher/Morrison Pro Stock team bought from me. My friend said "Buddy's bench has to be perfectly clean all of the time, I can have a couple of inches of head shavings in mine and it will still read ok."

Have not thought about his comment until I heard the french fry deal and started laughing!!!

Tom V.

[larrycavan]

[Nick]

Sorry if I ticked anyone off. When I perceive an injustice I open up both barrels so to speak. I think I made my point on that deal. My fries can go from 0-300fps in .002 sec.

So I tried a simple test tonight with a high delta P. I ran my incline manometer up the wall to the ceiling. I then marked it off by one inch. I selected #2 orifice. The head I was testing was flowing 165 on the #4 orifice. I then dialed up 36.5" of pressure difference on the incline, and 26" of test pressure. That was all my 4 2-stage motors were going to do. It works out to 169cfm. The gauges were just a steady as they were on the other orifice.


My theory of "violent jet streams" seams to not work out.

By the way, this is no laboratory grade testing here, I was just goofing around. So take it for what it is.

IF you read this post at 130am it just got changed, I was in bed and remembered I measured from the bottom of my wood scale when I should have measured from the 0% on the scale.


Nick

[Terry_Zakis]

I know this thread is about leakage, but some interesting points have come up about orifice vs. LFE's, so here are a few points which may be obvious to some but not others.

All of the reasons cited here in support of an orifice for measurement, are also valid in industry. If manufactured properly and not affected by non-uniform, pulsing, or spiraling flows, the orifice can give very good, and repeatable measurements.

In custody transfer with orifice meters, use of calibration is only done to verify that the orifice was manufactured/assembled correctly. After that, the calculation of the flow doens't rely on the calibration at all.

The laminar flow elements are also outstanding devices, but do have their limitations as cited above from contamination. As opposed to orifices, the LFE's depend 100% on their calibration, so if you get passages damaged or plugged, then the calibration is no longer valid, and your results will be in error. On the other hand, all you'd have to do is inspect, and clean the orifice plate and you'd be back in bussiness.

I have one 4-inch, and two 2-inch Merriam LFE's, and plan to use them for calibration/verification of my orifice based flow provers (which are external to the bench).

I'm also interested in using the LFE's to baseline the performance of the orifice flow provers, which have known limitations from turndown. As flow drops off through an orifice, and is no longer turbulent (defined as having a Reynolds number +10,000), the Cd would no longer be valid, and could give erroneous results. I have a few Dart flow computers that I'm setting up, which by design, are dual-range, having inputs for two Cd's (design flow range and then a low flow range). So in theory, the same orifice can accomodate lower flows, with a different Cd, and higher uncertainty in the measurement.

I also read a post a few days ago, that supported use of orifice plates in pipes, but I'm not sure if they were outside of the bench.

The one thing that amazes me about reading Tony's work, is his persistence in having a large plenum prior to and after the orifice, or as much as can be accomodated. When you take a step back and think about it, it's quite brilliant.

The ASME flow codes will show you that your measurement uncertainty goes down, as you increase your Beta ratio (pipe inside diam / orifice diam). So what Tony has been doing and advocating is use of an orifice that has a much higher Beta ratio than one could practically obtain within a pipe.

Best Regards,

Terry Terezakis

[Jesse Lackman]

If it was my post Terry, yes, the flow element will be in a pipe outside the bench.

I work at a power plant, where there are literally hundreds of flow elements of nearly every type measuring various gasses and liquids. Most are orifice flow meters.

I can't think of one orifice flowmeter that isn't in a pipe.

The standard X diameters before and after orifice pipe lengths separate the orifice from whatever else is going on in the system. I might have some disagreement here but this is the way it is at the power plant. There are systems that have many bends, pipes that go all over the place with control valves, blocking valves, reducers, transitions, pumps, etc. but it seems as long as there is X pipe diameters before and after the orifice, the flow reading will be accurate.

(What is happening in the orifice flow bench world is that "open" orifice standards are being set. The accurate way to use an orifice outside a pipe is being / has been (?) figured out. One still hears about big differences between flow benches.)

Anyway, this and orifice disk leakage are reasons why I decided to abandon the orifice disk / orifice disk board in the MercDog bench I'm building and move the flow element to the back of the bench - behind the manometer panel. I think this will be easier to deal with now that I decided to extend the back of the bench by 7". I'll have enough depth to play around back there.

Moving the flow element to the back of the manometer face and feeding it from the top of the bench will allow nearly the whole bench height for the flow element and standard X pipe diameter before and after straight pipe runs with flow straighteners. I plan to bring air out of what is now the valve chamber to the top of the bench (behind the manometer panel) route it down through a removable flow element, into the motor chamber, in there the piping will connect to a cyclone separator, and from there feed a small chamber (built in the valve chamber) directly under the test fixture. The flow element will be in a flanged pipe section and could be pitot, an interchangeble orifice, etc.

I could wet flow french fries with ketchup using this design and not pollute a pitot flow element. I want to be able to port the intake while the head is on the bench under vacuum. It would save time and be less messy.

--------------------------------------

One huge strike against an orifice IMO is the test pressure wasted across the orifice. A few posts up Thomas mentions 14" differential across the orifice. A pitot can develop the required resolution without wasting test pressure like that. Of course what this means in actual practice is that the bench would have 14" more test pressure available at the head fixture if it has a pitot instead of an orifice.

[Jesse Lackman]

Hey Nick, how do you wet flow the exhaust ports?

Do you suck through them or what?

I'm still trying to figure that out and could use a little advice....I'll probably suck through them so the cyclone separator can do it's job.

[Thomas Vaught]

Jesse,

I know a guy in Canada who built a "pipe orifice"
bench in his shop (30 ft ceilings) where the pipe came out of the bench ran 25 feet up the pipe to near the ceiling made a 180 degree turn and went back down a second pipe to the suction box.

He had a second set of pipes that took care of his exhaust flow, so basically a two orifice bench.

It was accurate but at some point he needed more cfm capability. He eventually bought a 5 hole
orifice plate and has been using that with good results since.

Lots of different ideas and they all work to some degree.

Tom V.

[Mouse]

I have never seen an airplane use an orifice to measure air velocity.

Working with Flow Performance FE series flow elements, I have never had to implement a correction factor unless I wanted to know ACFM.

I have only wrecked one flow element after the third time I dropped a valve into it. The third time I pushed the bent pieces back into place, one of them snapped off. I put a dab of epoxy over the hole where the piece broke off, put the element back into place, and it still worked perfectly without recalibration. So the element wasn't really wrecked, just a little balance defficient.

By the way, ALL benches can benifit from a saftey screen across the air way just under the test port. The Flow Performance bench recptacles employ a saftey screen inside the recptacle, preventing loose particles from being blown out, and from debri getting into the system.

Clay has never been a problem, just pull it off the element and continue on. Clay has wrecked some of my vacuum motors however.

When I was ready to test my new bench design, the Tower of Power, it took me about 3 minutes to place the pipe parts and the flow element into place on the bench. I set my FP1 to the base calibration number for the flow element, checked the calibration with one of Bruce's precision calibration orifices and it was right on the money.

Pitot tubes are not that bad.

Orifices and Pitot tubes have been proven to have about the same accuracy, about 1% typically. I happen to prefer Pitot tubes because of the flexability they offer in bench design.

John

[larrycavan]

I believe that would fall into the category of practicality of application.....

Aerodynamics and icing would be my first two guesses as to why it would be impractical to use an orifice setup rather than a pitot tube for aircraft...


JMO

Larry C