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December 12, 2019, 19:30:50 pm


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Author Topic: More of Chuckeroo's insanity  (Read 1892 times)
Garyhlucas
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« Reply #15 on: October 13, 2019, 18:11:26 pm »

A big factor on power require for vacuum hold down is leakage rate. If the leaks are small or non-existant the power requirements can be low. I hold down metal and plastic parts on a gasketed plate and I get about 13 pounds of force per sq.in.

Lloyds vacuum is likely a regenerative blower. It will use 20 hp at wide open air intake but once a part is clamped tight a wattmeter, not an ampmeter would show it using maybe 5 hp. I build waste treatment plants using these blowers and we have power logging from the VFD that runs every blower.

So a positive displacement lobe or screw blower on a VFD would be an optimum system providing the most grip for the least power.
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lloydsp
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« Reply #16 on: October 13, 2019, 21:22:23 pm »

Yeah, Gary... I SAID it was a regenerative blower! <grin>

I've not measured the power while clamping, but the best I can get is 10" Hg vacuum, even with parts clamped-down tight.  I've also not measured the 'down-force' that creates.

Perhaps, with your experience with such machines, you can tell me how much hold-down force I get per square-inch on material at that vacuum level.  I'd really like to know (no kiddin').

Thanks,
Lloyd
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chuckeroo
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« Reply #17 on: October 13, 2019, 21:29:11 pm »

Thanks dave i will keep all of this in mind.
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lloydsp
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« Reply #18 on: October 13, 2019, 22:09:50 pm »

'Couldn't avoid looking up the data!  At 10" Hg vacuum, I'm gettin 4.904psi on the worksheet.

Lloyd
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Garyhlucas
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« Reply #19 on: October 14, 2019, 18:16:32 pm »

Lloyd,
Yep that is a right and about the best you can expect from regenerative blower. On plastic with a rubber gasket using a venturi vacuum pump run by compressed air I can get about 25” hg. Venturi generators are very inefficient and only work well with small volume requirements.
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« Reply #20 on: October 14, 2019, 23:10:26 pm »

Hello

hg ?

Hectogram or inch (or mm) of mercury ?   Huh Huh

++
David
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Garyhlucas
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« Reply #21 on: October 14, 2019, 23:21:45 pm »

Sorry inches of mercury.
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Gary H. Lucas

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« Reply #22 on: October 15, 2019, 01:40:52 am »

David,
Not for nothing, but he WROTE 'inches of mercury', when he noted '...25" hg...'.

Those are the English language conventions for inches ("), and (except for capitalization) mercury (Hg).

He wrote - in English - exactly and precisely-understandable information for a native English speaker/reader.

Just sayin'! (Ain't Engrich strange?)

<grin>

Lloyd
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dave benson
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« Reply #23 on: October 15, 2019, 05:24:18 am »

Lloyd you seem you be doing ok, I compared the watts\p\Mbar of david's pump and  the one I think CNCnuts is using and it works out on paper at least, that your machine is capable of 40x the force.

I made a comparison between the vacuum cleaner,David's pump, and Lloyds pump, where the expectation was that all of the pumps (same type but very different configurations) would return a figure close to, or equal in value.

0.7 kw at 0.240 Mbar   vacuum cleaner
0.7 kw at 0.250 Mbar    David's Pump
0.7 kw at 0.280 to 0.338 Mbar   Lloyds 
(The devil in the detail here is David's pump cost's half as  much to run as compared to the vacuum cleaner so David's on a winner there).
That's pretty good measuring Lloyd your numbers are close, I suspect that's within the tolerance of what you measured it with.
I didn't know what you really needed and went and had a look at what the manufacturer (shopsabre) recommended Here:

https://beckerpumps.com/pressure-pumps/rotary-vane-pumps-pressure-pumps/oil-less-compressors/the-dtlf-series/

Your pump seems to meet the requirements and is not overly constricted or blocked either, or the numbers above would be in the toilet.
Could be blocked galleries in the table?

How have you determined that the table is not performing correctly.

F=P\A Force\Area pascals\sqm Pressure (Pascals) Area exposed to vacuum in (sqm).

Dave
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EddyCurrent
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« Reply #24 on: October 15, 2019, 07:40:04 am »

David,
Not for nothing, but he WROTE 'inches of mercury', when he noted '...25" hg...'.

Those are the English language conventions for inches ("), and (except for capitalization) mercury (Hg).

He wrote - in English - exactly and precisely-understandable information for a native English speaker/reader.

Just sayin'! (Ain't Engrich strange?)

<grin>

Lloyd

Here in England, inches of mercury or 25"hg all make perfect sense to me but I'm from the pre decimal era  Cheesy
plus my old stick barometer literally has a long column of mercury and the scale is in inches.

I just saw this though;

"Millibar
International unit for measuring air pressure. Now a hectoPascal (hPa) is the standard unit for pressure."


« Last Edit: October 15, 2019, 07:56:50 am by EddyCurrent » Logged

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lloydsp
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« Reply #25 on: October 15, 2019, 12:52:15 pm »

Eddy,
The more 'technical' one becomes, the more likely it is you'll use millibars.  As a pilot, I was getting pre-flight briefings from the Federal Aviation Authority in both inches of mercury and millibars, as far back as the mid 1970s.

Here in the US, the "common man's" unit is still inches of mercury, but millibars is creeping into daily language.

My table is fine, but the nature of the work requires that I have a 1/4" sheet of de-surfaced low-density fiberboard as the 'waste sheet'.  That cuts WAY down on the available hold-down of the work-piece itself.  Unfortunately, we must cut all the way through the work-piece over a large area of every job we run, so 'no backer' is not an option.

My blower is an Italian model -- something like "ZPV" or "VPZ".  I haven't looked at the tag in a year.  But I DO have a $5800 USD 'spare' sitting in the corner, lest something happen.

Lloyd
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Garyhlucas
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« Reply #26 on: October 15, 2019, 14:14:08 pm »

Lloyd,
I have worked with the Blower you have. It is a nice very well made unit, however make sure you have a good intake filter as it is one of the designs that does NOT tolerate any debris or it siezes up!  After siezing up 3 of them a couple of times each we finally figured out that in our pressure application short power failures were deadly.

The Becker blower referred to is another animal altogether. It is a positive displacement blower so the efficiency is high but unlike the lobe blower there is rubbing of the vanes against the housing so their maintenance is higher and life span is much shorter. They aren’t used in our business because we run blowers 24/7/365 until they need a rebuild. That’s just bearings on a regenerative, and might be gears as well on a lobe blower after lots of hours.

Screw blowers are getting more popular in our industry and now Turbo Blowers turning more than 20,000 rpm running on air or magnetic bearings!
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Gary H. Lucas

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lloydsp
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« Reply #27 on: October 15, 2019, 17:38:26 pm »

Ah... 'looked at the tag.  It's an FPZ 20HP unit.

Yes, we thoroughly filter the incoming air, and have a good filter on the vacuum-relief valve, also.  Because we sort-of 'pre-filter' the air through LDF, we check the filters monthly, but have only had to clean/replace them three times in its life.

This unit's got more than a decade of use, and the bearings still seem fine.  But like I said, there's a spare on the shelf, if it decides to upchuck.  When the theme parks call, you can't afford any down-time.

Lloyd
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Garyhlucas
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« Reply #28 on: October 15, 2019, 18:59:19 pm »

Lloyd,
Yes I knew you were think FPZ.  A decade of your use is likely only a year of ours.  So you are probably good for another 20 years!
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Gary H. Lucas

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lloydsp
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« Reply #29 on: October 15, 2019, 19:12:42 pm »

That's good to know, Gary.  Thanks!

Lloyd
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