Shop vac hold down

[Zumba]

The most powerful shopvac for a reasonable price I've found is a Milwaukee for about $600. It says it does 92CFM max and has a "sealed suction in water" of 134in. Does that mean it can pull a vacuum of 134 inches of water aka ~9.5inHG? Or does it mean something completely different?

[Kevin Taylor]

Are you wanting it for a vacume chuck why not use a refrigration compressor or evac pump you can get 27"hg out of a good one I us to use ones out of pop machines for doind refg recharges With the politcal incorectness of freon now you might find an old charging station cheep they have a real nice vac pump in them. Good Luck Kevin

[Geof]

Originally Posted by Zumba .. It says it does 92CFM max and has a "sealed suction in water" of 134in. Does that mean it can pull a vacuum of 134 inches of water aka ~9.5inHG? Or does it mean something completely different?

You have to be a bit careful with some of the claims for volume flow and suction. The 92 cfm probably means maximum without any hoses and it would not be surprising if the filter was not on. The 134 inches of water could be the level the water surges to; like you have the sucker running, dip the calibrated pipe into a water bucket and measure the highest point the water reaches as it has some momentum. That fact that it stabilises well below that is ignored.

[2muchstuff]

I would not recommend using a shop vac for vacuum hold down. The motors that they use are a flow-thru type. They need air flow thru them to keep them cool. If you block off the air intake (suction) the motor will overheat. Using an old refrigeration compressor is a better alternative. They don't have much CFM but they have a high suction.

[Zumba]

Thanks. I'm probably going to end up purchasing a 10hp regenerative blower for my 4x4 gantry. So far I've seen the Fuji from Grainger for $2400 and the Gast from MSC for about the same price. Any other contenders?

I wish Amazon sold this thing.

[Geof]

Originally Posted by Zumba Thanks. I'm probably going to end up purchasing a 10hp regenerative blower for my 4x4 gantry. So far I've seen the Fuji from Grainger for $2400 and the Gast from MSC for about the same price. Any other contenders? I wish Amazon sold this thing.

If you are getting into this type of horsepower and price it might be worthwhile looking at positive displacement pumps. You lose a little bit in volume but gain in negative pressure. Also they may be less noisy.

[Zumba]

Hey Geof,

By pos displacement, are you referring to roots type blowers? Can you recommend any specific units in the 10hp range? Thanks.

[mxtras]

The water ring pumps are good - so are the oil ring pumps - like Busch. They are higher maintenance and higher cost. They work well but I wouldn't suggest this route. They do not like moving a lot of air for a long period of time - this will blow all of the sealing oil out of the pump and cook it. They are pretty much maintenance pigs, but if you want relatively low volume and super high pressure, they are the pump you want. They can move a lot of air, but not for extended periods. They are better at building pressure.

The shop vacs aren't bad for a smaller table. I would recommend it - probably over anything else because of the economy of it. They are loud but you can dead head them all day and they will not overheat.

The regenerative blowers are probably the best option for bigger users. You can run them for extended periods dead-headed - they will get very hot but they are designed for running without air flow. Give them some ventilation and maybe a small amount of air through the pump and they will last. Maybe that depends on the manufacturer. They require good filtration but otherwise no maintenance. I have run 8HP blowers continuously with very little leakage more times than I can count while compacting pre-preg composites many years ago - only burned one up and it was brand new, so I believe it was defective. Inadequate clearance or crap built up on the impeller will send it to an early grave.

Scott

[Geof]

Originally Posted by Zumba Hey Geof, By pos displacement, are you referring to roots type blowers? Can you recommend any specific units in the 10hp range? Thanks.

I suggested positive displacement as another option but I cannot give a specific recommendation. I believe Gast makes them and Sutorbilt is another manufacturer.

Another option is to spend your money on a good compressor and then use venturi vaccum generators. This approach means you also have plenty of compressed air and you do not have to get as concerned about dust or liquids being taken into the vacuum system.

[mxtras]

You may also want to zone your table - a 10HP pump sounds excessive for a 4'X4' area - but then again, I have no idea what the particulars are for your application. I currently operate a 6'X12' zoned table machine with an 8HP oil ring pump made by Travaini(sp?) with an Agip pump. I guess it depends on what you are doing and what your table looks like.

Hold down with vacuum depends on what you are doing - no doubt, but I think for most routing situations you won't need the super high pressures - you need more recovery potential to maintain a minimum hold down force which equals high volume, not high pressure. Having a good distribution network with minimal loss is important. With nothing on your table and the pump running, you want to see the lowest differential between the trunk line near the pump and the directly below the table. Additionally, the table surface should not be restrictive, either. A minimal gage reading under the table when the pump is running and the table surface is completely empty is a good indication of a non-restrictive surface. Hard to achieve, but something to strive for.

For 15 years I worked at a company that made ultrasonic cutting machines (in addition to other machines - including routers) up to 180 feet long that used zoned vacuum tables and the majority of what I was cutting was lofty continuous strand fibergalss mat. We would also contract cut other fibrous goods as well as sheet goods for a huge variety of companies - mainly aerospace and textile industries. We predominantly used blowers. When higher pressures were required to counter higher cutting forces, like when cutting Titanium honeycomb materials for example, we would process on a smaller table with water or oil ring pumps. Most of the pumps were made by Busch. I can't recall who makes the water rings but I am sure Google would turn up a number of potential folks making these pumps.

I can't agree with Goef this time. I can not stand using compressed air - it is not anywhere near effecient. Electrical and maintenance costs combined with initial installation costs gives it a black eye for me. It's necessary - yes, but I would not recommend using one inefficient process to drive another. Not good economy in my mind. Sorry, Geof. They have their place, but the drawbacks for this application are too numerous for the gains. Just get a pump or use a big ShopVac or two.

Scott

[Geof]

Originally Posted by mxtras I can't agree with Goef this time. Scott

I would forgive you if you spelled my name correctly!

I agree with everything you say in terms of the negatives of compressed air; I did say it was an option to consider. Perhaps I am biased because I was lucky enough to pick up a 15hp 60 cfm rotary screw compressor for $1500 and I am located in a place with very cheap electricity.

[Zumba]

Great info, Scott,

Geof, your comment on the venturi piqued my interest. I happen to be in the market for a new compressor to power spray guns, a line boring machine, and various pneumatic clamps around the shop. I was planning to spend about $1000-1500. I was also planning to spend 2500-3000 on my vacuum pump. If one will do both, I won't hesitate to combine the two budgets.

How much CFM are you getting out of your venturi system? I understand that a venturi is easily capable of pulling full 29inHG vacuum.

P.S. I have an extra 80 Gallon Tank sitting around that I can use as an auxiliary.