PTS Flowbench Forum

--->the DM should be mounted flat with the label facing up.

Uh... the Digital Manometer?

Crap. Mounted on it's side, label facing outwards (vertical).

M

The plate in our box is for 300 CFM, diameter 2.045.

We have tried each of our other 2 plates on the top, one for 200 CFM (1.669) and one for 100 CFM (1.18) with similar strange results.

Any ideas as to why the CFM reading doesn't go to zero when all fans are off? It is zero when we start the software before starting the fans.

Simon

Simon, the internal plate is measured at 16" DP so at 2.045 it is roughley 225CFM you should not realy be trying to calibrate a 200CFM at 28" plate on top of the bench with this plate inside. A 300CFM at 16" plate would be closer to 2.390".

I asked this above because i want you to understand the differance so you know how the bench works.

Rick

Rick:

Ok, now I'm confused.

Why isn't the 300 cfm plate also for 28" depression? I don't have the plates here with me (at home), but they have two different calibrations on them for two different depressions. I thought all three plates (100, 200, 300) had a 28" reading...?

WIll verify all this tomorrow evening, and likely post from the shop where the Bench is in case we need "timely" responses!

Thanks again to all for reading and responding. We are horrible--but well-intentioned!--newbies.

M

Internal plates need to be rated 25cfm more than the plate or part you are testing. This is in the plans area or Flowsoft area in discussions somewhere on the forum.

The digital manometer will not allow you to test a plate/part to the same cfm as the internally plate is rated, it runs out of "range" on the sensor.

The DM will read correctly on it's side but it's zero reading will be wacko when it's not laying flat on it's "bottom" once air is applied it works as designed.

We all have been at the newbee stage and this is how we learn and pass on our knowledge, sometimes it's hard to get something across or it be understood in the correct manor and that's fine we all understand and have no problem going over things again . . .

Bruce:

Thx.

At this point, I don't believe we'll be testing anything that flows much more than 250 cfm on our 300 cfm bench (manifolds, maybe?) and the valve flow is likely to be in the 130 to 180 range.

I've reread the Calibration instructions and from what I've surmised I don't think we went back and 'tweaked' the discharge coefficient. That's my guess at this point. We'll start fresh tomorrow, do the whole thing again.....

RE: DM. So, IF we keep it on it's side, is it NOT worth bothering to do the "Channel Offsets" to get a zero reading, because it's just not going to do it anyway? At the moment, I don't think the DM is easily mounted horizontally (depth of box area a problem), but we'll double-check this tomorrow.

We'll also try to use the velocity tube to check for air leaks (read that somewhere...)

One other question, just for curiousity: is this bench also able to work in "floating pressure-drop" mode? (ala David Vizard's preference). Not trying to complicate things, just curious as to its' flexibility.

Thx!

M

Mounted on it's side you will more than likely have to use a channel offset for CFM channel. Again it does not add to your end number if it shows any reading at rest. It just shows something other than 000 with no-flow.

I don't know anyone using a PTS design flowbench as a floating depression flowbench? Probably the nicest way I can say this

M,

OK let’s see, if you look at the plates Bruce gave you they are marked for both 16" and 28" pressure differential the 16” number will be lower than the 28”. Bruce does this as a convenience to the end user so they do not have to DO THE MATH based on where they use the plate.

Note:
The PTS bench in designed to work with varying TEST depression 0 to 36” on the standard DM. But the internal plate DP (Delta P) > “Differential Pressure” is fixed at 0 to 16”. That said if you do the math on your 2.045 plate it should flow 300 +/_ CFM at 28” but since the internal DP is only set to a max of 16” this same plate will only flow 225 +/-CFM at 16” when used inside the bench. “REMEMBER THE INTERNAL PLATE DICTATES THE BENCHES/DM MAX FLOW RANGE” Thus the internal plate range should always be slightly higher than the expected test part maximum flow. Example if my head at 28” is expected to flow 200CFM I would want an internal plate that can at least flow 225CFM at 16”.

DM Orientation; Why for the life of me the CFM channel wants more offset when the DM is mounted on it’s side is puzzling me and I intend to work with Bruce to get to the bottom of it as mine is mounted in this same manor. You can adjust the offset for channel 2 incrementally until you zero out; That said the effects of returning to ZERO are also affected by the number used in averaging, to big and it takes longer to get back to zero, to low and the numbers are twitchy.

Last; It has been asked of me on many occasions by the forum and by Bruce to incorporate Auto Zero in the FlowSoft program. I think this has value but I am still trying to work through adding a safety net to this process as it could also mask a damaged DM. So until I do further testing I am going to leave it in the manual mode.

M, you need to get comfortable with the ability to calculate flow through and orifice, there are spreadsheet on the forum to do this, but it is the concept that will help you to understand the flow/pressure differential relationship better. And this all translates to understanding??? The port a little better I/E things like curtain area and effective CSA are all interpretations of this math.

Good luck

Rick

UPDATE as promised:

First, we put in a shelf and mounted the DM horizontally. This made the "zero readings" between 7 and 13 (rather than the 20 they had been before). At this time, the operator chose not to chase after the channel offsets, preferring to refer to Bruce's comment that it "won't matter" to the actual readings, and we proceeded onto the calibration.

The 300 CFM plate is installed. We calibrated with the 100 cfm plate and everything was pretty good-- hit both 16" and 28" numbers within 1.5% (low cfm).

When we then tried to calibrate with the 200 cfm plate, we could hit the 16" number-- but NOT the 28". The best we got was 18" of depression and around 155 (? not sure on this number)

For shits and giggles we tried calibrating in Exhaust mode and got similar but even lower results-- an error more like 5%. (For instance, instead of reading 148 cfm on intake mode it read 143 cfm on exhaust mode.)

We have the (4) 80CFM motors installed (220V). Are these just NOT enough oomph? (you'd think they would be...). Our test last week had MUCH higher numbers (I remember looking over the shoulder and seeing 315cfm on the screen at one time), but we weren't even close to calibrated last week so not sure if that was a true reading or a computer reading.. :-p (All we'd changed from last week, physically, was to reseal the top plate.)

OUR NEXT STEP: the exhaust mode had found a small leak at one of the access doors and we've resealed that. We're going to do some electrical (amperage) testing to see what the motors are pulling, how stable our electrical feed is, etc. We also, just for goofs, are going to put the DM back to vertical!

We found the numbers to be "twitchy" (as Rick says)-- is this normal? Or is it an indicator of either varying voltage or a still-leaking bench? By twitchy, it's this: the 100 cfm plate would vary in depression from 27.6 to 28.07 (say) with cfm readings of 97.4 to 98.8, etc. (don't quote me-- I'm just remembering visual impressions.)

I'm pretty sure we could start using the bench with the 200cfm plate and do cylinder head readings, but I don't want to start 'meaningful" testing until I'm positive there are no flaws in the bench. (Cuz, otherwise, we'd have to pitch the results.) If the motors just aren't up to snuff, then we can do the lower range testing now and add two motors later. If the motors *should* be enough for a 300 cfm bench-- then we've got something else going on, still. (This is My gut feeling, though I don't have much for ideas at the moment.)

Thoughts? And can someone explain, in layman's terms, how we use the velocity probe to check for leaks? Neither of us understood those instructions. :-/

Cheers,

M

Did you follow the instructions on page 5 for DM calibration?

The 16" number is ONLY a concern for the plate range when it's inside the flowbench. This is the CFM range of the plate.

The 28" number is the one you use for calibration when the plate is on top of the flowbench.

So the "300" plate is in fact a 226 @16" plate when it's inside the flowbench so it can read a max of 200cfm@28" so the 100@28" plate would be the late you use for calibration purposes on that plate.

If you use the 450@28" plate (340@16") then you would use the 300@28 and 100@28" for calibration.

You would use channel 3 in inches of water mode and hook a tube to the negative side and you have a "leak detector" that reads inches of water. This is run around any joint or part and it will sense a leak as movement in the reading on Flowsoft. If you add a length of small diameter tubing you make yourself a leak detector wand.

When you want to test velocity just hookup your velocity probes per instructions and switch channel 3 back to FPS and you have feet per second . . .

I'm trying to get around to doing a video showing this whole process but it's been tough to get something done being one person, the holidays and life things (new grandson) also got me behind on this.

Ah!

Well, then you need to put that in the Instructions! "Find the plate(s) whose 28" number is LESS than the installed plates 16" number, and use THOSE for calibration..." THAT would be more clear. We were struggling with a 200 cfm @ 28" plate!

Based on what you've said, then, we were fine: the "300" plate is installed and it calibrated fine (or near enough-- needs one tweak of the discharge coefficient) with the 100cfm plate.

We will run the leak detector anyway. Thanks for that.

But I still have the questions:

a) ARE four motors going to be enough to test at ~300 cfm? If the "300" plate is actually only 226 @ 16" (for "range"), then we likely need still a BIGGER plate (one size up) because some things we test will be in the 250 range....

b) Are the "twitchy" readings "normal"? We are going to do voltage checks tomorrow (weather permitting) to see how stable our voltage is and what the individual draw and vacuum of each motor is. (We thought we noticed that the #4 motor, while you would hear it turn on, seemed to do little to aid the CFM..)

Thx!

M