PTS Flowbench Forum

Tony wrote:I tried something like this a very long time ago, and it does work.
Two identical orifices in series will generate equal pressure drops. its really interesting because the absolute pressures and air densities are different, but the differential pressure drops end up being the same.

Ain't nature a wonderful thing !

Tony,

What distance between orifices? And what volume? I have decided to try to make a very simple change to my big chambered bench, namely making the pre-orifice chamber on the verge of silly large.. that should replicate that feat. I hope.

Yes it should replicate.
The main requirement for accurate measurement is to have as undisturbed air as possible up stream of the orifice.
A settling chamber simply cannot be made too big.

Been busy and forgot about this. Did you ever get the problem sorted out? If so, what was wrong?

Tony wrote:Yes it should replicate.
The main requirement for accurate measurement is to have as undisturbed air as possible up stream of the orifice.
A settling chamber simply cannot be made too big.

No brainer..... calm is better than turbulent

Brucepts wrote:

SWR wrote: What I am asking is if any of you have in essence zero pressure loss in your benches? If you have a 6" rise on your inclined manometer, and you pull 6" of test pressure, and both orifices are identical in size, you will have pressures of 0" before the test piece / 6" after it and also 6" before the flow orifice / 12" after the flow orifice when you pull 100% on the inclined, hence zero flow loss through orifices. Is that even possible given that both orifices have identical sizes?

I have never done this test on my bench reading the same static as depression testing, Rick and I chatted about this last evening on the phone and I'm going to do some testing on it. I am machining a few sets of customer orifice plates either today or Tuesday and can test the plates against each other at my rated internal DP pressure of 16".

As a design note I over-rate my internal plates by 25cfm so I am not up against the max on the digital pressure sensor. I also recommend on calibration plates they be rated at ~80% of the scale cfm for calibration, I find this number works the best. No specific reason for ~80% just what I have found over the years that works for all bench designs I have supplied calibration plates for.

Might be a day or two before I get to run this test on my flowbench, I have a few orders to get finished this week.

Please clarify your calibration and CFM rating method for your plates.

If I have a PTS calibration plate with a xxx CFM written on it. Is it to be used to calibrate xxx CFM or (xxx CFM * .8)?

If the plate is to be used internally and is marked xxx CFM, is it really (xxx CFM - 25)?

I totally get it with over pressure situation. That's got nothing to do with my questions.

Please clarify your calibration and CFM rating method for your plates.

If I have a PTS calibration plate with a xxx CFM written on it. Is it to be used to calibrate xxx CFM or (xxx CFM * .8)?

If the plate is to be used internally and is marked xxx CFM, is it really (xxx CFM - 25)?

I totally get it with over pressure situation. That's got nothing to do with my questions.

PTS Orifice plates are rated as marked if is has 28/16 flow rates on the plate then that is the given CFM of the plate In example a 200CFM at 28" is actually 200CFM at 28" if the plate is marked 325CFM at 16" it is a 325cfm plate at 16" there is no math involved in these plates except if you are trying to use them at an alternate pressure as say 25". Bruce will not sell you, or guide you away form buying a 300CFM at 16" internal plate for a PTS Bench to allow room for sensor over pressurization on a 300CFM calibration plate that's all.

Rick

larrycavan wrote: Please clarify your calibration and CFM rating method for your plates.

If I have a PTS calibration plate with a xxx CFM written on it. Is it to be used to calibrate xxx CFM or (xxx CFM * .8)?

If the plate is to be used internally and is marked xxx CFM, is it really (xxx CFM - 25)?

I totally get it with over pressure situation. That's got nothing to do with my questions.

To clarify; if your scale (water or digital) is 100cfm the calibration plate I would recommend is 80cfm, 200cfm would be 160cfm, 300cfm would be 240 etc . . . some flowbenches on the market have various end ranges that are odd numbers, in that case I spec plates in what I consider "normal" numbers for ease of use as close to 80% as possible. This allows one to compare someone else's flowbench to another if they are all using my plates. As you know I can machine plates in any size that would be needed and I don't put the customer into a one size fits all, if someone would want a 223cfm@28" plate or some other what I would consider "weird" number I will machine it for them. I usually discuss this with someone when we work on plates for non-PTS flowbenches, I already have ranges worked out to work with the PTS Bench design with my DM.

Plates flow what they are marked so the internal plate cfm is what it is capable of flowing. But, it's over ranged by 25cfm per my design, it is still marked 625 or what other range is required by the customer. There is no conversion math needed by anyone using my plates.

larrycavan wrote:Been busy and forgot about this. Did you ever get the problem sorted out? If so, what was wrong?

Nope. Still bugging me. I'm into re-working the 2-chamber bench now so I can try that. Tony said 2 identical orifices will give identical pressure drops, but I am still waiting for Bruces test results too. I need to know, do not have time to spend weeks figuring out how to get this to work again, I have loads of flowbench work pending..

SWR wrote:

larrycavan wrote:Been busy and forgot about this. Did you ever get the problem sorted out? If so, what was wrong?

Nope. Still bugging me. I'm into re-working the 2-chamber bench now so I can try that. Tony said 2 identical orifices will give identical pressure drops, but I am still waiting for Bruces test results too. I need to know, do not have time to spend weeks figuring out how to get this to work again, I have loads of flowbench work pending..

Been a tad busy here with orders, hoping to get the lathe setup today to run a batch of plate orders, I'm finishing up some velocity probe parts on the lathe right now.

SWR, I went back and reread your original post and as usual I had some reading comprehension issues! Am I correct in stating that in the way you are testing that if you Teed the test pressure (Vertical Monometer) into the high side (upstream ) of the orifice taps and ran your test the 300 cfm test part would flow correct it is only when you Tap the test pressure just under the test part that you get the pressure loss issue?

For clarification can you please explain the T plumbing in the picture, is it a pressure adjusting valve?

Rick