First time using vac chuck - mysterious black dust cloud!.

[Dan Forman]

So I finally got to use my vac chuck, am happy to report that the bowl remained firmly connected for the entire operation.

One surprise, however, was that when I removed the bowl, a small cloud of black dust materialized - there was also some what I assume is graphite dust stuck to the inside of the bowl. :eek: It came out with some naphtha, probably should have tried to blow it out with the air hose, but i didn't think of that at the time.

So is this to be expected, or should I have used the relief valve to let the pressure down to release the bowl? I have all of the filters (3) in place just as in Steve's directions. No dust came out of the muffler, I assume it just backed up into the chuck when I shut off the pump. Has this ever happened to you? I was drawing about 23" of HG while in progress. It was a small bowl on a 4" chuck.

Edit: see follow up posts, I think is's safe to say the dust isn't from the pump!

Dan

[Don Geiger]

I can't wait to hear the theories on this one!

I've used vacuum chucks for years, not only in my shop; where I have two, but at others as well and have never seen anything like this. I have also used rotary vane vacuum pumps throughout my carreer in scientific applications and have never heard or seen of such a thing.

Don Geiger

[Tim Rinehart]

That's an odd one for sure....I shut my pump off, holding lightly to whatever is on the chuck, and then wait for it to gently release into my hand. I'd hate to think there's something breaking down in your pump that backfed...but even that seems implausible...though I suppose anything is possible.
One thought, regardless of source of this 'dust', is to give your piece a coat of shellac or lacquer (if consistent with whatever final finish you plan) to the area where the chuck seal is made. There's always a possibility of transferring some of your gasket material coloration, in my experience, and this helps reduce amount of sanding to remove anything which could work into grain. Quite often, I'll coat an entire piece on outside with shellac or lacquer to help seal up pores that would otherwise cause leakage. On alot of woods, you can feel the vacuum pulling right through the wood, especially once your wall thicknesses get pretty thin.

[Antonio Martinez]

I have an opinion on this ....here goes...don't throw rocks - they hurt!

Since the 'input' to the system is through the headstock, two things jump to mind...(1) filters will not have any impact on your question because they are past the input. (2) - I think what you found is either dust from sanding or material that was literally sucked from the wood. My reason for this is wood is pourous and you're drawing a near perfect vacuum. The system has to 'suck air' from somewhere and that's through the wood. If you did any sanding prior to mounting in the vacuum chuck, any grit that was left behind would have no place to go but 'into' the system which is air through the wood and then into / onto your headstock plate. Likewise, if the wood has/had any dirt/dust/critters in the wood, it would get sucked through and have no place to go but 'into' the system. THere's where your filters will help (imho).

I use a vacuum system to 'suck' finish into wood to stabilize it, add color, and other ideas that sometimes work and sometimes don't. It's interesting to see what I sometimes find in the vacuum chamber after I finish with my process. It usually looks like dirt and is very fine - which may be what you saw and are calling graphite.

As for having a relief valve, I have one. I keep the pump running and then open the valve to remove the wood from the headstock. I like this method as it gives me control over it just seemingly falling off.

Tony.

[Dan Forman]

The dust was black, the bowl was light colored, so it wasn't sawdust from sanding. The output air is clean, somehow the dust worked it's way back through the system and into the bowl.

Dan

Edit: disregard, see my next post

[Steve Schlumpf]

Dan - just my opinion - but - I would think your inline air filter would prevent anything from flowing from your pump to the bowl. I wonder if removing the bowl without first releasing the vacuum through your relief valve - you would cause a rush of air at the point the seal of the bowl was broken. Even though that rush of air would be extremely fast - it might cause a venturi effect and pull any debris from inside your spindle.

Looking forward to finding out what it actually is!

[Dan Forman]

Further info: With the aid of some backlight, I see that there is a black deposit on the inside of the tubing that leads from the lathe adaptor to the input filter. It's much darker in the 1/2" tubing spanning the input filter and the manifold holding the gauge and needle valve, and progressively lighter from the manifold to the lathe adaptor. Everything past the first filter is clean. I just ran another test, putting a piece of plywood over the chuck to seal, and ran the pump without the lathe rotating, which would eliminate the possibility of something going on in the adaptor being the culprit. Result was a similar blackish dust cloud coming out of the chuck after about 5 minutes of running time when the plywood was removed.

Due to the clarity of the tubing of the rest of the system, I don't see how this could be anything coming back through the pump, so my guess is that rather than graphite, it is PVC dust coming from the pipe used for the chuck. The vacuum must be causing the pipe to "leak" tiny bits of itself into the low pressure area while the pump is running. I can't think of any other explanation. Will try to cover the inside of the pipe with shellac or something else that would seal it, and see what happens. Any material scientists in the audience who care to offer an opinion?

I think that the most material clings to the 1/2" hose that leads into the first filter, because the air is moving slower then, due to the increase in volume of the larger diameter hose (from 3/8" hose coming from the lathe), possibly aided by the resistance of the filter, so it would have an easier time settling out onto the interior surface of the hose.

I would welcome any other thoughts you might have. The system can be seen here:
http://www.sawmillcreek.org/showthread.php?158617-Vacuum-system-finished.&highlight=

Dan

[Dale Miner]

HI Dan,

It seems to me that pulling dust sized particles of the pvc loose is not likely.

The link of pics of your system does not show the vacuum chuck and associated seal that you are using, and also does not show the rotary adaptor that you are using, so the following may be off base.


I can think of three sources of dark colored dirt.

1) The sealing gasket you are using is breaking down and shedding the dirt particles you are seeing.
2) The seals in the rotary adaptor are deteriorating, and when the vacuum pump is shut off, a backflow of air from the pump/filter is carrying the debris from the seals back into the bowl. Some rotary adaptors use graphite/ceramic seals, and are not intended to by run dry. If the adaptor uses ceramic/graphite seals and ceramic portion is cracked, it will rapidly wear the graphite part. If the adaptor uses a rubber or neoprene seal, these seals may be failing and result in the particles you are seeing.
3) There was dirt in the spindle prior to your first use of the system, and the backflow of air is carrying the dirt into the bowl when the pump is shut off.

I believe the shutdown procedure for most vacuum pumps calls for removal of the 'load' by allowing a free flow of air through the pump for a minute or two before shutting down. This is to help cool the pump parts and prevent the load from causing a run back of the pump. You may already be in the habit of opening your bypass valve prior to shut down. Letting the pump run unloaded for a minute or two after opening the bypass valve would be a good habit to get into.

I have the same exact pump, and have not noticed any dirt in the bowl after use. I do open the bypass valve and allow the pump to run for a short while before shut down. I don't think that I ever close the bypass valve completely, usually just enough to get 10 to 15 inches of vacuum. I would think that if the pump vanes were failing, you would see dirt in the hose and filter on the outlet side of your pump.

A couple of questions. Do you leave the rotary adaptor in place when the vacuum system is not in place? What rpm's do you run the rotary adaptor at when in or not in use? Does the rotary adaptor get warm or make noise when the lathe is running?

Later,
Dale M

[Josh Bowman]

Dan, I get a little very fine black stuff in my filters also from my Gast vane pump. I just attribute to the graphite vanes in the pump wearing some.

[Dan Forman]

Dale---The sealing gasket is white closed cell foam, so I think that can be ruled out.

The rotary adaptor is brand new, from JT Turning Tools. This was the first time it was used. It has some kind of rubber O-rings which appear to be in good shape. It appears to run quite smoothly, is quiet, and I found the same amount of dust with the lathe running on the first attempt to use the chuck, as in the second test with the lathe off. I then ran the lathe with the adaptor in place but the vacuum off, removed the adaptor and tapped it, opening down, on a piece of wood, so that if anything was wearing inside, the dust would fall out and on to the board, but nothing came out. Hence, I think that can be ruled out as well.

I had blown the spindle out with compressed air several times while operating the spindle tap when making the chuck, so I think that can be ruled out too.

The dust can't be coming from the pump, because there are no deposits on the hoses beyond the first filter.

As unlikely as it sounds, the only remaining source for the black dust would be the PVC pipe used in construction of the chuck. The dust is so fine it looks like smoke, lingers in the air rather than settling out quickly.

After the first time, I remembered about letting it run without load, did it after the second test, and will in the future. The needle valve doesn't open fully, so the only way to get the piece off the chuck is to shut off the pump.

Here is a pic of the chuck (middle) : The foam was clean and white before using it.

The white donut you see (last) is the inner surface of the gasket from the chuck. I removed it to clean the pvc prior to coating the interior with something. As you an see, the discoloring is pretty extreme.

The first pic is the lathe spindle adaptor, the nose of which is covered with this "soot".

Dan

[Dan Forman]

Josh, this is coming well upstream of the pump, and before the first filter, so has to be from the chuck or the adaptor. I'm sure I will get some of that graphite from the pump eventually, but none is showing yet.

Dan

[Dan Forman]

Well, I just sprayed the PVC with white enamel, inside and out, so tomorrow will give it another try. If there is no more black dust, I can blame the PVC. If there is dust, it must be the adaptor. Will post the results.

Dan

[Doug Wolf]

Dan,
I have the same system and was puzzled at your black dust until you posted the picture of the vacuum chuck your using. Mine uses WHITE PVC and I think its your BLACK ABS causing you grief.

Make a new chuck with the thick wall 4" coupling and I'm sure your problem with the dust will be gone.

[David Lancaster]

Hi Dan

I think what is happening is when you shut off the power the vacuum within the tube and the pump is caused to vent back through the tubing bringing with it any of the carbon particles from the veins. This dust would normally be trapped it the exhaust filter but because the system was going backwards it escaped into the bowl causing the problem.

A rotary vein pump should never run in reverse it will cause damage to the veins. What I do is mount a check valve at the pump so it won't be able to go in reverse, If you mount the pump on an old compressor tank it will give you a safety backup if something happens like loose power.

I hope this helps

[David Lancaster]

Dan

If your pump is a gast remove both filters intake and exhaust and blow them out also blow out the pump. If this was the first time the pump was used in a long time who knows when it was cleaned last

[Dan Forman]

David---I took the face off of the pump earlier, and it was clean, the vanes in good shape. It is surplus, but never used. There is no sign of dust anywhere else in the system, it's all between the lathe and the first filter, so I don't see how it could be coming from the pump, though that was my first suspicion too. I'll give the newly painted chuck a try soon and post results.

Doug---I think you are on to something, I didn't know that there was a difference between the black and the white plastics.

Dan

[Dan Forman]

Please help--- my brain hurts!!!

So I painted the black pipe inside and out with white enamel, let it dry for three days (that stuff dries slow!), and fired up the pump again with the lathe off and a piece of plywood covering the pipe, white packing foam as a gasket. I let it run about 10 minutes, this time I opened the relief valve, and pulled the board off when the vacuum got down to 4". No puff of dust, but then there wouldn't be with vacuum still applied. So I turned on the pump again, replaced the board and let it run again for five or ten minutes, then shut off the pump, the board fell off, and out came a puff of dust, though didn't seem like as much as before, and the gasket wasn't discolored at all, there was just a trace of soot on the inside surface of the now white pipe. This is where my theory of the dust coming from the pipe falls to the ground.

The problem is, I don't see how this could be blowback from the pump, even though it feels like graphite, as it would have to get back through the filter the opposite way, and there is no visible deposit on the outside of the filter, nor is there any deposit on any of the tubing downstream of the first filter - though there is plenty on the tubing before the filter, in the filter, and all the way back to the lathe spindle. It just doesn't make any sense to me. I hope someone can explain this phenomenon, before my head explodes. :confused::confused::confused: I understand how blowback might happen, but why all the soot in the front part of the system, and none near the pump, where it would originate from? The lathe wasn't running, so I don't see how the adaptor could be the source.

Dan

[Fred Perreault]

Dan, is that black PVC pipe? As in solid black sch. 40 PVC? Just asking, but I don't believe that I have ever seen that in this area, and I have been putting in septic systems for decades. Must be a Left Coast thing... :)

[Dale Bright]

Dan,

I think it is the pipe you used and even with painting it, there was most likely a little dust left in the system for blowback when you shut it off.

I am pretty sure you bought ABS pipe and here is a link that will show the difference in ABS and PVC. ABS has a foam core that might have caused the original dust.

http://www.ehow.com/about_6079874_abs-pipe-vs_-pvc.html

Dale

[Dale Miner]

Dan,

Now, having seen the pics of your adaptor and chuck and system, I'm puzzled too. The test you just performed by opening the relief valve to drop the vacuum before removing the plywood resulted in a clean chuck interior, the test where you shut the pump off without opening the relief valve caused a dirty chuck interior. My guess is that there is blowback occuring, and the dirty interior from your second test is a result of the blowback bringing dirt from the filter and hose back up to the chuck.

The source of the dirt is definately a mystery. Some thoughts: The filter is not doing it's job, or is plumbed or designed in such a was as to allow the blowback to let the dirt bypass the element, or the graphite particles are smaller than the filter media can capture. Your upstream filter looks to be plumbed in a way that the captured dirt will be inside the filter and difficult to see without removing or cutting open the media;

There was dirt in the system somewhere (filter, chuck, adaptor, ?) before the initial use, the hose and filter media are now contaminated with the dirt, and the blowback brings it to the chuck on pump shutdown;

The tailstock does not line up perfectly, and some of the ABS was fretted off and contaminated the system (not likely, but...).

Disassemble all upstream hoses, filters, and blow them out with compressed air and wash the interior of the hoses and filter housings with soap and water to remove the dirt that is present on the upstream side of the pump, and take the downstream filter out of the system and allow the pump to discharge into free air until the systems problems are found;

Use the bypass valve for all shutdowns in the future to eliminate the possibility of the pump running backwards and blowback pulling captured dirt from the filter into the upstream part of the system.

I do not have a filter on the outlet of my pump, and have not noticed any graphite particles coming out of the outlet. I always open the bypass valve, dropping the vacuum to a couple of inches and pulling the turning from the chuck prior to shutdown. I seldom use more than 10 or 15 inches of vacuum to hold items on the chuck (4.5"), using the bypass to regulate the vacuum. This does keep some flow of air through the pump at all times. I do think that shutting the pump off under load is to be avoided to prevent pump damage.

Later,
Dale M

[Dan Forman]

Ok, I probably don't do my best thinking at 3 AM. When I woke up today, I came to the same conclusion as Dale Bright . When the pump is shut off, there is some blowback, but it's not carrying graphite from the pump. There is a fair amount of buildup of black residue inside the filter, but none on the outside. This must have come from the pipe before it was painted. The blowback was stirring up some of that, creating the smaller dust cloud in the last instance. There was no buildup on the foam because there wasn't a constant supply of ABS entering the system, as the pipe was now painted. I think I will replace the needle valve with a ball valve, which should give me a clean release from the chuck without having to struggle with the bowl to pull it off, and prevent any blowback from happening, which should protect the pump as Dale M. pointed out. I am still open to alternative theories.

Dan

[Jon Prouty]

Hi Dan

I would try another chuck - a white PVC coupling. Make a bigger one than your existing one (you will eventually anyway) and clean out the system and retry. I also believe the problem is from the ABS.

Good luck!
Jon