Thread: The evils of shop vacs

Hi John,
Why not put it out side, & with a open cover. not sure what your wall is, but maybe a bit cleaner.

Well you are preaching to the converted here John.

After testing a whole bunch of shop vacs last year I can tell you that what you see is 1% of what is going on.

Most low end shop and domestic vacuum cleaners (VC) "are very inefficient at filtering fine dust" simply because their filters are very inefficient.
Manufacturers testing and testing organizations like Choice ONLY focus on visible dust and tests are done with sand or flour picked up from a hard surface or carpet. They never bother to test the amount of fine dust that pours out the back through the filter.

HEPA filtered VCs are better but Just because a VC says it is HEPA filtered (Like motor HP ratings) this does not mean much.
There are standards like the EN 1822 and MERV ratings but unless the VC comes from a reliable manufacturer then I would not trust the VC to meet that standard.

Most VCs "make more fine dust than they collect".
They do this in two ways.
1) The normal collection method and loop uses high speed air flow which smashes a few big dust particles into many little ones.
On cheaper VCs the fine dust comes pouring out the back. More expensive VCs with HEPA filters work fine but rarely stay this way for long.
All portable VCs that get pulled dragged around a workshop get beatup and develop leaks.
All VCs fixed will in time develop leaks across seals, filters and bags etc.

2) The motor on VCs need cooling, so manufacturers add a small air cooling loop. This cooling loop (even on very expensive VCs) is very rarely filtered. The loop only needs to pick up a few big dust particles from workshop air and the motor effectively minices these into fine dust and this contaminates the motor and being unfiltered this dust pours out the back of the VC.

The older a VC the more likely it is to be able to contaminate your workshop. During my study of DCs and VCs, Most VCs that were more than ~5 years old produced contamination above the 1mg/m^3 OHS limit, and all (including the more expensive ones) produced high levels of the very finest dust for which there is unfortunately no OHS level. In one case a very expensive VC was only a few months old and was badly contaminated.

Most of the VCs I examined were not what I would call well maintained. Motor cooling loops, seals and internals of VCs required regular cleaning and maintenance and filter replacement. The internals and outside of a VC and motor cooling loops should be regularly blown out with filtered compressed air while the motor is running, and the surrounding air scavenged using a DC that vents outside the shed otherwise it will recontaminate the motor.

If you really wish to keep the motor cooling loop of a a VC clean, it should not be used in a dusty environment which kind of defeats the purpose of a VC.

Now to solutions.

1) Putting the VC outside the shed
This will mean using ducting or additional hose of some kind. It is important to note that this hose or duct cannot be too narrow or too long or it will reduce the flow rate. No VC should use a total length of more than about 5m of narrow hose. If longer hoses are added to the VC or the box then they should 50 mm or more in diameter.

2)Place the VC into a sealed box that vents to the outside of the shed.
John, in your case the VC being in a fixed location makes it easy but most VCs are portable so we are back to the long hose problem.
This sealed box will be under some pressure and needs to be well sealed otherwise leaks will defeat the purpose of the box.
Dust will accumulate is such a box as the air speed through the box will be too low to hold even fine dust in suspension. This will make a reall mes when it comes to clean out the filters and bags

3) Vent the box into a DC duct.
Note the box should NOT be sealed.
This should really only be done if the DC is outside a shed for the same reasons as the DC should be outside the shed
This has 2 benefits. Firstly it overcomes the long narrow hose problem and it will negatively pressure the box so that box leaks are not an issue.
A big benefit is the VC filter can be removed as it only restricts the air flow and since the DC will catch the fine dust you never have to change the VC filter. If you do this you should be aware that the inside of the box may accumulate some dust and it may make a mess when you go to empty the VC. If you decide to do this then some vents need to be strategically added to the box so that it can breathe and help the DC remove the dust from the box.
Also note that Some VCs require a filter in place or the motor may overheat and burn out.
One downside of the box method is it may reduce the mobility/portability of the VC. The other is you use more power running both devices.

4) use a cheap blower vac with it's exhaust vented into a DC.
Blower vacs make it much easier to exhaust the fine dust direct into a DC duct so the filter can easily be removed from these units and this means the filter never needs cleaning (proviso that motor might require filter still applies) and you also may not even need a box. The issue of VC leaks and motor cooling loop contamination also still applies but if you are running a DC anyway it appears the DC can scavenge sufficient air from around the VC to capture the contamination from leaks and the motor cooling loop. I have tested this with my "side of the road pick up" blower VC and so far it seems to work very well (see https://www.woodworkforums.com/f200/v...r-vacs-169705/). Once again the DC needs to be outside the shed and the same downsides as for 3) applies.

Issatree,

Still considering putting it outside, but in my situation that makes for a very long hose, and loss of suction.

Another issue is that I could not see the little red light that tells me the canister needs emptying, but that is not mission critical.

Originally Posted by John Samuel

Issatree,

Still considering putting it outside, but in my situation that makes for a very long hose, and loss of suction.

Another issue is that I could not see the little red light that tells me the canister needs emptying, but that is not mission critical.

If you put it in a box you could locate an acrylic rod on top of the red light such that the rod passes to the outside of the box.

Bob,

The red light is not an issue if the vac stays in the shed ... only if I put it outside.

This is a Hoover Garage vac. The motor is at the top of the unit, and it has a crude cyclone/canister at the bottom.

There is a small hole in the side of the vac through which air is sucked into the vac. My guess is that this air is used to cool the motor ... does that sound about right?

If I enclose the vac, then the air drawn in through that hole is likely to be laden with invisible dust. Could this be an issue, especially for motor wear/cooling?

The more I think about it the more I lean towards putting the beast outside. The vac came with 9M of hose, and at 1,600 W is pretty powerful. Thinking about putting it outside and running a 50mm PVC pipe into the shed. A shorter length of flex hose would then be used to connect tools to the system. Mt total length of duct would be a little longer, but not a lot, and resistance in the PVC pipe would be low compared to the flex hose.

Because I now use the cyclone with a 100mm flexy to vacuum the floor, the vac needs only to extract dust from tools and to clean up drillings etc from on and around my work benches. The only remaining issue would be the red light ... but if I did nothing about that and checked the vac every day or three, is that really an issue?

Also, I may be able to ditch the filters if I put it outside, meaning the only maintenance is emptying the canister. Does this sound reasonable?

In addition, if the beast is outside, I can ignore leak issues.

So, it seems that the kind of thinking that led me to buy a Clear Vue (ducting outside etc) should lead me to put the vac outside. If I wanted I could have more than one PVC connection point for the flex hose and cap off any unused port. That would keep the flex hose used even shorter.

I have even considered stripping off the plastic body and venting the various exhausts outside, but that still leaves me with the possibility of leaks.

The Clear Vue now does an excellent job of keeping my shop (and its air) clean. Yesterday I shaped four cedar legs on the wheel of my linisher ... did not bother to cut the basic shape with the band saw. See pic. It was quick and easy ... and clean.

IMAG0295[1].jpg

Because the dust collection at the linisher is now excellent, my shop and its air stayed clean. There was a time when this would have filled my shop with dust. The vac is one of the few remaining dust issues, and I am keen to finish the job well.

Originally Posted by John Samuel

The red light is not an issue if the vac stays in the shed ... only if I put it outside.

You can make a flexible light pipe that could pass back into the shed with some PVC tube filled with water and seal both ends with clear epoxy

There is a small hole in the side of the vac through which air is sucked into the vac. My guess is that this air is used to cool the motor ... does that sound about right? If I enclose the vac, then the air drawn in through that hole is likely to be laden with invisible dust. Could this be an issue, especially for motor wear/cooling?

Should not be a problem as the density of the dust is still low enough not to worry it. Remember ordinary air has a lot of invisible dust in it already.

The more I think about it the more I lean towards putting the beast outside. The vac came with 9M of hose, and at 1,600 W is pretty powerful. Thinking about putting it outside and running a 50mm PVC pipe into the shed. A shorter length of flex hose would then be used to connect tools to the system. Mt total length of duct would be a little longer, but not a lot, and resistance in the PVC pipe would be low compared to the flex hose.

This should be OK especially if your remove the filter.

Because I now use the cyclone with a 100mm flexy to vacuum the floor, the vac needs only to extract dust from tools and to clean up drillings etc from on and around my work benches. The only remaining issue would be the red light ... but if I did nothing about that and checked the vac every day or three, is that really an issue?

See comment on red light above.

Also, I may be able to ditch the filters if I put it outside, meaning the only maintenance is emptying the canister. Does this sound reasonable?

Yep - that would easily make up for any loss in flow by using a longer hose, but bear in mind that some VCs don't like it of you remove teh fikter.

In addition, if the beast is outside, I can ignore leak issues.

Yep

Good to see you are able to get on with your woodwork.

OK ...

Am pretty sure I've talked myself into putting the beast outside.

Measured it up. About 7M of 50mm PVC pipe and about 4M of flex hose are required. That's a total of 11M compared with 9M of flex hose fitted standard. Given the PVC will have lower resistance, I should be OK. I might start it with about 6M of flex hose and test the suction ... easy to shorten if the suction loss bothers me.

The issue occupying my thinking right now is filters. BobL mentioned that some vacs don't like to have their filters removed. Is there any way I can determine this?

Originally Posted by John Samuel

OK ...

Am pretty sure I've talked myself into putting the beast outside.

Measured it up. About 7M of 50mm PVC pipe and about 4M of flex hose are required. That's a total of 11M compared with 9M of flex hose fitted standard. Given the PVC will have lower resistance, I should be OK. I might start it with about 6M of flex hose and test the suction ... easy to shorten if the suction loss bothers me.

The issue occupying my thinking right now is filters. BobL mentioned that some vacs don't like to have their filters removed. Is there any way I can determine this?

One way it to use a power or current meter. If the meter(s) power or current readings remain at the specified rating you are safe. if they are above the rating thats when you need to be careful. VC's don't usually change much because the restriction to flow is the narrow pipe size rather than the filter.

You indicated that it is a 1600W unit which means it should draw 1660/240 = 6.7 A, If the unit still draws 6.7A with the filter out you will be OK. If it draws more (say 7.5A) I would run it and monitor it carefully to see how hot the motor gets. A good unit will have a thermal cut out and if this kicks in you'll know theres a problem but this is not really the way to do it.

It's quite tricky to check the temperature of a VC motor as they are often encased in plastic ect. You could perhaps monitor the air temp of the motor cooling loop compared to when the filter is in it, but this is no guarantee the motor will be safe.

Anyway the first step is to see if the running current changes.

Thanks Bob,

That gives me an excuse to buy a multimeter.

I'll try to pick up the bits and pieces needed later this week and will ... hopefully ... soon be able to report success.

Originally Posted by John Samuel

Thanks Bob,
That gives me an excuse to buy a multimeter.
I'll try to pick up the bits and pieces needed later this week and will ... hopefully ... soon be able to report success.

In case you are not aware a multimeter alone is not a safe way to measure mains current. A safer way is to use a current clamp around the active wire so there are no exposed conductors involved. Some current clamps can read and display the current directly while other less expensive ones produce a low voltage signal output that can be read by a multimeter so it is still a good idea to get a multimeter but while you are at it look at current clamps as well.

Thanks Bob,

Already onto it.

Was about to order a clamp multimeter yesterday ... looked good ... inexpensive ... but just as I was about to hit the "buy" button noticed the small print: "User manual in Chinese Language."

Pass. Paid a few bucks more for one with a manual in English.

Am planning to use 50mm PVC pipe for the ductwork. Is there likely to be any benefit in increasing this to 90mm? Should I be concerned about the drop in velocity? I'm thinking the vac will pick up nearly all very small particles (sanding etc) and that 90mm should be OK, but also thought it wise to check.

If you move the vac outside, you could add a mini cyclone or dust deputy to the inside so that you can easily check and clear the bulk of the dust. Not sure how much grunt you will lose but it would be a lot more convenient.

Hiroller,

Those separators gobble up a lot of grunt. Bill Pentz's site reckons about 4.5" of WC ... and that's a bunch. Even at half that, I would likely struggle, especially since I have a reasonably long run of pipe/hose.

Originally Posted by John Samuel

Am planning to use 50mm PVC pipe for the ductwork. Is there likely to be any benefit in increasing this to 90mm? Should I be concerned about the drop in velocity? I'm thinking the vac will pick up nearly all very small particles (sanding etc) and that 90mm should be OK, but also thought it wise to check.

at the ~100 cfm flow rates of VCs 50 mm pipe will be fine.

FWIW
At these flow rate
50 mm pipe has a pressure loss of 0.4 " of water per meter of duct
90 mm duct has a pressure loss of 0.02" of water per m
27 mm duct has a pressure loss of about 12" of water per m

At VC pressures of ~70" of water you can see that narrow hoses are are problem.

Of course this does not mean that a VC will deliver 100 cfm with a 5 m hose and zero cfm with a 6 m hose. The pressure drop reduces the flow so that some air always continues to flow. The reason that such narrow hoses are used is to maintain high air speeds to gather dust at source.