PTS Flowbench Forum

Hi guys,

I haven't been on here for ages. I have used a fairly unconventional bench for nearly a decade. It's an orifice-in-a-tube design much like Kevin's (Performance Trends) EZ-Flow design. 125mm tubing, that's 5" for you. I have industrial software that lets me calculate the accurate orifice flow according to the ISO 5167 standard to 3 decimals no matter the side wall effects and such, so knowing what flow I should have is no problem.

But. The problem now. I moved it, as in completely took it apart and moved it, now I am reassembling it to a slightly more compact form after a de-tour via a typical orifice bench, that showed too much flow at all times.. just like this now. I did not get the math to work out on it, but now it seems more like I have forgotten something about the setup of a bench as this current bench, although a very different design, shows the exact same numbers - too much flow for the test pressure - like the other one.

Now it's suddenly impossible to calibrate... so I wonder what I have forgot in the 7-8 years since last time. I did have this exact issue before too, just did not write it down back then... The pressures I get with a 305 cfm / 10" inside the bench and a 300 cfm / 10" as the test piece leaves me to wonder. 10" incline, as mentioned, when I check it I hook both the inclined and the vertical to the flow orifice pickups. Adjust the inclined to show 100% when the vertical shows 10", then the physical rise of the inclined also is exact 10". When I then connect the test pressure to the pickup under the test piece, it shows 100% flow on the inclined when my test pressure is just 7.5"...?? Swapping the upstream orifice pickup with the test pressure pickup makes NO difference, so no big pressure drop for that distance. Pressures is as can be seen in my totally awesome Paint-sketch.
Any ideas why it shows 100% Flow at 7.5" TP? It needs a rise of about 13" on the inclined to reach 10" test pressure on the vertical...

No leaks in the hoses. I have ran a leak test with the inclined at 12" rise that showed 2 cfm leak at 70" for the full system, hardly worth mentioning. The distance to the orifice from the last bend is about 5 feet, distance after the orifice is 8 times the tubing diameter, so that should be fine.

Any pointers? As I mentioned, the big-chambered "normal" flowbench I 99% finished before I gave up showed just the same. So what have I forgot??

The size of your incline well could be throwing it off?

It's the same wells I used before. It's 2.5" diameter and has a rise of just 1/8" between 0 and 100%.

Some thoughts......
From what I see [first cup of coffee this morning after a very late night last night].

Seems to me it would either have to be a leak somewhere or an inaccurate manometer like Bruce said.

Leak in the green outlined tubing?
Manometer fluids the same in both manoms?

Swap the manometers, one for the other...see what the readings are?

Add a 3rd manometer and verify the other two against it. Perhaps also measure combined pressures with that one. See what that number is while the other two are hooked up normally with an orifice being tested. If it were a two chamber orifice bench that would be the test pressure DP plus the DP across the internal orifice. You'd get that by connecting a manometer to the lower side of the orifice chamber and atmosphere with the other leg.

My mind isn't yet awake enough to figure out that connection on your particular bench...

On second look, I see 17.5" indicated to the left of what appears to be the orifice in the tube. That would be the correct total pressure based on what you're indicating the pressures are from the two manometers combined. 10 + 7.5.

Don't know what you used to measure that value??? "IF" whatever gauge you used to measure that with is verifiably correct in accuracy then the problem would seemingly a leak somewhere in the piping.

The point I'm trying to make here is that you FIRST have to know that you have a 100% accurate manometer with which you can verify the other two manometers. If one of those is inaccurate and it was used to obtain that 17.5" value, you'd be on a wild goose chase with no hope of catching the goose...

larrycavan wrote:Some thoughts......
From what I see [first cup of coffee this morning after a very late night last night].

Seems to me it would either have to be a leak somewhere or an inaccurate manometer like Bruce said.

Leak in the green outlined tubing?

approx 2 cfm at 70".

Manometer fluids the same in both manoms?

Water + one drop of industrial coloring agent.

Swap the manometers, one for the other...see what the readings are?

Exactly the same.

Add a 3rd manometer and verify the other two against it. Perhaps also measure combined pressures with that one. See what that number is while the other two are hooked up normally with an orifice being tested. If it were a two chamber orifice bench that would be the test pressure DP plus the DP across the internal orifice. You'd get that by connecting a manometer to the lower side of the orifice chamber and atmosphere with the other leg.

My mind isn't yet awake enough to figure out that connection on your particular bench...

That's what is described on the sketch. I think. That's how I got to the 17.5" pressure after the orifice.

larrycavan wrote:On second look, I see 17.5" indicated to the left of what appears to be the orifice in the tube. That would be the correct total pressure based on what you're indicating the pressures are from the two manometers combined. 10 + 7.5.

Don't know what you used to measure that value??? "IF" whatever gauge you used to measure that with is verifiably correct in accuracy then the problem would seemingly a leak somewhere in the piping.

The point I'm trying to make here is that you FIRST have to know that you have a 100% accurate manometer with which you can verify the other two manometers. If one of those is inaccurate and it was used to obtain that 17.5" value, you'd be on a wild goose chase with no hope of catching the goose...

I'll hook up a simple U-style vertical manometer today to see if it says the same.

Then I have tested with a separate U-type manometer, it shows the exact same value as my vertical manometer on the bench. I did some reading on the Flowbench 101 section and there it said you could not flow it with a test piece of the same size of the internal one? Is it something I do not understand..? As long as it is not bigger, it should be fine, right?

Very good. Your manometers check out when verified against another.

In the drawing I added A,B & C.

For Value of 17.5 @ Location C to be true then A to B Dp would have to be 10 instead of 7.5.

Assuming C as Total Pressure, 7.5 as Delta P across the Internal orifice. Providing I'm looking at this correctly.

1 = Inclined Manometer
2 = Vertical Manometer
X = Atmospheric Tap
Y = Flow Feed Pipe Tap

If 1 & 2 don't read identical when connected to X & Y then one or the other is reading inaccurately.
Not likely that the actual inch scaled manometer is reading incorrectly BUT possible the inclined scale could be incorrectly laid out.

What happens if you eliminate the inclined from the picture, hook up the U Tube in it's place and calculate flow from
Formulas instead of % reading?