Re: Is there a problem with this vacuum pump?
Hi,
vane vacuum pumps are good for low and even very low ultimate vacuums, but really thats not what you want for a vacuum hold down.
Lets say a vane vacuum pump can get down to 0.1 psi from atmospheric of 14.7 psi. If you had a 100 square inch workpiece te hold down force would
be (14.7-0.1)*100 =146 lbf. Note that 0.1 psi is about right for a single stage vane pump.
Lets say a liquid ring pump can get down to 1psi from atmospheric, its hold down is (14.7-1)*100=137lbf.
Really the difference of the hold own force between the two pumps is negligible. The real test comes when there is considerably vacuum leakage. The ultimate vacuum of the vane pump
will suffer badly. Liquid ring pumps however tend to have MUCH higher swept volume and the degradation in vacuum and therefore degradation of the hold down is less.
If you bought a HUGE vane pump the leaky vacuum will matter less, but otherwise a liquid ring pump offers superior swept volume and for less money.
Vane pumps are great when you need a really good ultimate vacuum, say degassing epoxy, or vacuum desiccation. For vacuum hold down with leaky vacuums
you need the highest possible swept volume.
Craig
Re: Is there a problem with this vacuum pump?
Quote:
Originally Posted by
joeavaerage
Hi,
vane vacuum pumps are good for low and even very low ultimate vacuums, but really thats not what you want for a vacuum hold down.
I respectfully disagree. Oilless vane pumps are often used in woodworking machines.
Quote:
If you bought a HUGE vane pump the leaky vacuum will matter less, but otherwise a liquid ring pump offers superior swept volume and for less money.
He kind of did buy a HUGE pump. A 6kW pump sounds almost like an overkill for a 600x1200 table. We use 7kW pumps for machines with five times larger work area.
Re: Is there a problem with this vacuum pump?
Thanks for your comment! I will refer to the advice. But since I have already purchased it, I would like to know if this pump works on a 1200x600 table. Rest assured that we also have a 2.2kw ring blower!
I don't know the details, but I understand. So I chose a big pump.
Re: Is there a problem with this vacuum pump?
Quote:
Originally Posted by
toshio
since I have already purchased it, I would like to know if this pump works on a 1200x600 table.
I don't see why it wouldn't. Whether it's the best choice, that's open for discussion. But it will definitely do the job.
Re: Is there a problem with this vacuum pump?
The reference to leakage is the important aspect.If you are using a gasket beneath the job and the spoilboard isn't too permeable,a lower flow rate has a chance.On a large MDF spoilboard with too few zones that can be de-activated you would need a high flow rate with less ultimate vacuum rating.I would have thought that with a 600X1200 table the 2.2Kw pump ought to be adequate.Have you verified that there are no leaks and that the connecting pipe is not restricting flow?
As for small jobs,what exactly would be a small job?There is a point when even a perfect vacuum can't generate enough holding power to restrain a tiny piece in the face of a hefty stepper pushing a tool in a hurry.Even if you have done things like adding a piece of melamine HPL to the remainder of the relevant zones to reduce the leakage.You may find it necessary to reduce the depth of cut so that the cutting force is less than the restraining force on some tiny pieces.In the event that you are cutting several small parts from a sheet that covers most of the table you may find it best to run two stages of cut so that the first goes 95% of the way through and then a much lighter final cut does the rest.
