FlowBench for 150 to 210 cfm heads - FlowBench Materials

[Tony]

A quarter inch orifice is an extremely sensitive flow measurement. But it will give you some sort of a definite baseline number with which to reference total air leakage. There may be more than one leak, so as you work your way around the bench, any small improvement can be readily quantified.

Mix up a bucket of laundry soap suds, and place great arm fulls of bubbles around the outside of the bench. The corners can be particularly leakage prone. But don't forget the panels themselves can also be slightly porous. But soap bubbles are a fairly good indicator. They will either rapidly expand in size, or shrink down to nothing fairly rapidly at the exact point of air leakage.

[200cfm]

Ok, thanks for the update. Now I understand. Will make up some soap bubbles.

[larrycavan]

[200cfm]

I tried bubbles around the corners and ends today and could not detect anything. But I am suspicious of the inner boards that butt up against the back and front panels.

I haven't added any kind of motor one way valve/flap control on the exhaust side of the motors. Would that potential back flow from say a motor not running affect the leak test or other tests?

Do you have to paint MPD? I was thinking it would be dense enough. I plan to paint but didn't think MPD would be an immediate leak source concern.

I ran the numbers and from what I can calculate I have at least 6 cfm + leak at a potential 28" test stall on the tiny .250" leak plate orifice. I can't test that high because the incline would overflow but converting the test pressure to 28" wc gives 6 cfm leak numbers.

[200cfm]

Ok, over the days I removed the rear panel. MPD board does not like separating from silicone II. Added lots more silicone after cleanup and added bolts in between the screws to pull the board into the frame tighter. Painted the insides and outside with latex primer. And sealed up ever joint line possible with overkill. Wanted to remove the motor board and try a complete reseal there also but it was not removeable. Simply to tight and hammering things would have destroyed the board so decided to reinstall the motors and seal up with overkill. And added a 5th motor for cfm insurance if bench shows a better seal. 5th motor is installed but not wired yet.

Got in some data tests late this evening. If I am interpreting the data correctly the seal is better. Not perfect but seems to be better. I recalibrated the manometers in parallel. Then with the top of the bench sealed and selection of the tiny .250" home made orifice this is what I get.

12" wc test depression pulled 35.8 cm on the incline. 100% incline is at 76.2 cm length. I calculated that to be about a 2 cfm leak. And when I converted the test pressure to 28" test that becomes 3 cfm leak.

Using less motor power a 4" wc test depression pulled 4.4 cm on the incline or .7 cfm if I am using the math correctly. A 5.2 " wc test depression gave a 8.8 cm rise or 1 cfm across the .250 orifice.

Then I blocked the .250 orifice just to make an observation. Could barely get .1" wc on the test depression and incline pulls to 45 cm. Not sure how to interpret what this means.

Finally I put on the calibration plate 115 cfm @ 28" wc from the 1.266 orifice. Selected the 1.300 orifice which is suspose to give 79.4 cfm @ 100% for a 12" incline rise.

Result was 12.4" wc test depression pulled 76.2 cm rise for 100% incline. How do I interpret that? Is that 79.4 cfm plus my leak or minus my leak?

Next, selected the 1.650 orifice. Suspose to offer 127.9 cfm @ 100" incline 12" rise or 76.2 cm distance mark. Most I could pull was 66 cm on a test depression of 25" wc. All 4 motors were pulling but could not make a full 28" test depression level? Does that mean I have to have the 5th motor?

Finally, selected the 1.950 orifice. Suspose to offer 178.6 cfm at 100% rise on the 12" incline. Now I can make the 28" inch test depression fine with the 4 motors humming but pull ony 35.5 cm rise on incline. Made several pulls and it repeats within 1 mm at 28" test.

Please evaluate the data to see if I have a credible bench at this point. And should I consider a lower test depression? Thanks.

[larrycavan]

Not being able to pull 28" of test pressure on the second to largest orifice but being able to pull it on the largers one indicated something is wrong. I don't know what your orifice board looks like but I suspect a leak related the the second to largest orifice based solely on the test results.

[200cfm]

Ok, I ran the tests again today. Got pretty much the same data. I can pull a full 28" test depression on the 1.950" orifice. And the incline will rise up to 66.5 or 66.4 cm level. That converts to around 93.25% flow or about 123.7 cfm. Now since the top entry is using the calibration plate 115 cfm @ 28" test I assume my adjusted leak is 123.7 minus 115 or 8.7 cfm. So yes, I can definitely pull 28" test on the largest orifice.

But a repeat test on the 1.650 peaks out at 24.8 to 25. " wc test depression. And the incline max rise is 66.5 cm or around 93.25 % flow across the selected 1.650 orifice. That figures out to around 11 cfm difference between the two pressure drops.

1.300 orifice selected gave easy 100% rise on less motors at 12.4 " wc test depression. Error difference between the two orifices is now only 3.2 cfm.

I don't have a stopper for the largest orifice. Have been using duct tape to close it off when not selected. Other two have rubber stoppers. But I don't see how that could be making the 1.650 plate not reach a full 28" wc test. And I would think it is not the motors since they can pull the number on the 28" wc on the largest plate.

What is the .250" test plate data indicating? Thanks.

[Thomas Vaught]

Need to get a proper plug on the largest hole to run the second highest range properly, not duct tape. Even if you make it out of wood in a "T"
shape and use an "O-ring around the bottom portion of the "t" will work.
Make the bottom portion of the "T" very slightly smaller vs the hole diameter and use a weight on the Flat portion of the "T" to keep the "o-ring" tight to the orifice surface.

Tom V.

[bruce]

Be VERY careful with the sharp edge orifice plates you can damage the sharp edge real easy!

[larrycavan]

How about a pic of your orifice board setup?

A couple of things are obvious at this point.

1. You need to wire up the 5th motor.
2. You need to have a 100% effective sealing method for the orifices that are not in use while paying attention to NOT damaging the sharp edge.

Rather than having all the orifices in the bench at once and using plugs, if it were me, I'd fabricate an orifice board with a quick change setup and use ONLY 1 orifice at a time. I take great care in protecting the sharp edges of my calibration plates and use an entirely different plate inside my bench. I adjusted the Cd value for the bench orifice to fine tune it.

JMO

[SWR]

[200cfm]

Ok, will try and find a cork or proper sized rubber stopper for the largest orifice 1.950". Hope this is the problem. And will study how I might be able to clamp seal the front panel better. It currently opens after screw removal and I question the clamp seal portion along the middle portion where the motor divider board has to separate the top plenum from the suction side. Just don't think the back or side panels are a leak source anymore. Thanks.

[larrycavan]

[larrycavan]

[200cfm]

Ok, that's a good leak tester thought. Will give it a try tomorrow if things thaw out. Found a hardware supplier that offered a rubber stopper for the large 1.950". today. So all the plates now have rubber stoppers. And picked up some T nuts to install along the center front framing to pull the center front board tighter. May have to reexamine the sealing material on the front board. It is currently standard 1/2" wide house door seal. I can get a good "crush" up against it but it might still be trying to spunge air through.

Nothing here that time and money can't solve. And I am not to far from the river and perhaps that would tell me if it floats.
If not perhaps the fish can find the leak. The wife thinks the house never got the attention this bench is getting. Thanks for all the help.