Central ShopVac - Success or failure????

[Jim Neeley]

I'm in the final layout of my new workshop, which includes the new Clearvue Cyclone I've just received. My plan is to build an enclosure around the Clearvue anyway, so am considering making it 3'x6' and placing one or two of my shopvacs in it, each with a HEPA and a small cyclone up front. The vacs would then wye together into either a 2" or 3" line with various drops around my shop. The longest drop on this would total about 60' of pipe plus the pick-up hose. Are there others here who have tried something similar before? I've considered the 3" to reduce the pressure drop however I worry about maintaining pipe velocity, given that it will neck down to a 2" or smaller hose at the tool end.

With DC's maxing about 15" and shop vacs maxing at about 90", it didn't seem like the pressure drop would be a bid deal in 2" line with 2 vacs but I'd appreciate learning as much as possible from others experiences.

[Michael W. Clark]

If you are connecting your vacs parallel, the flow will add and the pressure will be that of a single vac. I would consider the 2.5 or 3 duct.

[ian maybury]

I'd be wary of pressure drop over what sound like pretty long hose runs Jim, and would want to check CFM and pressure drop against duct size before selecting a duct size and/or deciding it's feasible. Googling 'Cincinatti Fan Engineering Data' should bring up a .pdf with a flow chart - a ducting size/CFM/pressure drop chart going down to duct sizes of 1 1/2", 2", 3" and upwards.

Linking two vacuums (presumably in parallel) begs some questions about what the resulting combined performance might be - and there's some potential issues to watch out for (some of those mentioned won't apply in the case of your set up). http://old.greenheck.com/technical/t...multfansystems

Not sure how you might extrapolate to get to a combined fan curve to enable proper use of the ducting flow chart for paired vacuums (or even what the curve for a single one looks like), but Googling might bring up a means of calculation.

Failing that maybe hook up some test set ups and see how they perform...

ian

PS added later after a quick dig. Most vacs claim about 100 - 120 CFM at 100in WG. The 4000FT/min airspeed rule presumably still applies for effective transportation. Hard to know what paired vacuums might deliver, but say 100 - 150CFM if it's to be useful. Extrapolating (but this is only guesstimation) to the RHS of the tabled figures in the CF chart suggests that 100CFM gives about 4,000ft/min in a 2in dia smooth duct for about 25in WG pressure drop/100ft of duct run.

3in dia looks too big - it drops the airspeed too low for effective transportation at any reasonably likely CFM - but 2 1/2in might offer some promise at very roughly 15in WG/100ft run - IF (and its a big ask) the airflow is up around 150CFM. (what happens when the filters start to block, or the inlet is restricted?)

One issue is that two vacuums in parallel have the same pressure capability as one - any improvement in capability will be in CFM or airflow. It's not immediately obvious how you would do it, ot if it would be safe or feasible - but two in series approaches doubling the pressure capability for the same CFM as a single vacuum. This might suit a very long duct run better.

There are vacuums units designed to pull over long runs as a part of a centralised household vacuum system. Wonder (a) how they do it (presumably they use a higher pressure fan), and (b) if it might not be better to dig up one or its industrial equivalent (there's a fair amount of information put out by vacuum manufacturers for use by punters designing DIY central vac systems), and keep your mobile units for other uses??

Presuming no insurmountable technical issue, I wonder if it'd be possible to find a way to exhaust a built in vacuum system using a professional vacuum unit (maybe the air only, not necessarily air + dust and chips) into the return duct to the cartridge filters on your main dust system? It'd be better if you didn't have to run the main system every time as well, and in that case it'd take a solution to stop the air exhausting out of the inlets to the main system. (maybe an interlocked electrically operated blast gate that would also be wired to open when the main system fan is run) If it could made to work it could be a practical way to get HEPA filtration, and to save the cost of the horribly expensive filters sold for mobile units...

[glenn bradley]

I have a 50' x 2-1/2" hose and a 6HP (yeah, right) Shop Vac. I don't know about on paper but, the suction drop is significant in practice. I only use it when I really have to. 25' of hose seems to be "about" the same as 15' of hose. I haven't tried the 15' and the 25' hooked together but, somewhere before you get to 50', . . . well, let's just say that your expectations need to be pretty low . Now, a serious industrial unit like hotels and such use would surely fare better as would rigid ducting but, my consumer level unit (Ridgid) does not like the long run.

[Phil Thien]

I run a Ridgid "6-HP" vac with approx. 25 feet of 2.5" clear piping and eight blast gates. Works well for me. As long as one takes steps to reduce leaks, I don't think I'd have any problem doubling the lenght of my pipes.

After all, look at the length of pipe in some home central vac systems.

[Jim Neeley]

Hmm.. Since I don't need the 2-in-parallel for volume purposes (since I have the Clearvue), it appears that either a single shopvac or (per the Greenheck link it appears my ability to handle large SP drops will be significantly increased) two in *series* may be a better solution. Sounds like I'll have to try it but seems like a worthwhile endeavor. Also sounds like a good time to have my ammeter set up.

Just thinking but with two in series and the filter on the first removed I should be able to handle good flow at a pretty large pressure drop.

I wish the Cincinatti curves went above 10" pressure drop though.. that gets me 3000fpm in a 2" pipe.

As for pressure drop, I'm actually looking at something like Rockler's 2.5" clear plastic pipe, not hose, so that will be very helpful.

Edit: I wrote this on the 12th but just posted it today.. looks like I was on track!

[ian maybury]

You should be able to extrapolate/extend the Cincinatti Fan chart to the RHS without too much trouble or loss of accuracy Jim to get figures for air speeds and friction losses higher than are printed on the chart.

The friction loss in inches of WG/100ft scale at the bottom is what's called a log scale.

This means if you look closely at it you'll see that the spacing of the vertical lines/graduations isn't regular - but that it repeats the same pattern as you move from left to right. There's three repeats - one from 0.01 to 0.1, one from 0.1 to 1, and the third from 1 to 10.

Just add a fourth repeat/group on the same horizontal spacing as the above three - to the RHS starting on the last '10' line, and label them 10, 20, 30, 40, 60, 80, 100 as the others.

The other variables you will be interested in for inches duct diam and fpm velocity (feet per minute) are defined by straight lines, and can be extended as needed for whatever readings you want.

Some test running would be no harm to find out how the two vacuums react to running in series - just in case of heating, their not delivering the expected pressure or anything like that...

ian