I had customer call this week who was using an E-Vac model 800008H, an 8 SCFM Porous Vacuum Generator, to pull a vacuum on four vacuum cups. He was trying to lift a part with the four vacuum cups placed on a clean metal portion of the part. Unfortunately he was having a little trouble. He had to lift the product very slowly because the part could easily be dislodged, if the part was bumped or came to an abrupt stop.
The problem is a relatively simple one. The customer choose a porous vacuum generator when he would be better served with a non-porous unit. The vacuum cups are attaching to a non-porous surface, sheet metal, in a relatively clean environment. The difference between porous and non-porous units is that porous units has more vacuum flow available at a low vacuum level, where the non-porous vacuum generators have a higher level of vacuum, but less vacuum flow. Because of the high vacuum flow, a porous unit is much better for lifting porous materials like cardboard, some particle boards, and fabrics. The higher vacuum flow of porous vacuum generators helps maintain the vacuum when pulling upon materials which let a constant flow of air through. In the customer’s case, he was lifting a clean sheet of metal, a non-porous material, and needed a higher vacuum level as opposed to a higher vacuum flow. A higher vacuum level [more inches of mercury (Hg) of vacuum] would pull harder upon the metal and hold it tighter.
Let’s look at the customer’s example more closely. An EXAIR model 800008, porous E Vac, will generate a maximum of 21 inches of mercury (“Hg). A model 810008, non-porous E Vac, will generate 27 inches of mercury (“Hg). Let say he was using a 900758 3 1/4” diameter round vacuum cup. If you look at the Vacuum Lift Chart, you see that the 900758 can lift 42.8 lbs. at 21 “HG, but it can lift 55.0 pounds at 27 “HG of mercury. So in this application the customer can increase their lifting capacity by 28.5% by switching from a non-porous vacuum generator to a porous vacuum generator.