Vac Truck Hose Angle

I've never been a fan of, "steep angle and suck" if I could, "plunge it in and blast".

tcmtech is exactly right, and if you are wondering why, read on.

The reason is that the process of getting any media (particulate or liquid droplet) into a vacuum hose is governed by the drag coefficient you can induce on the particle. This is based on the particle's shape and the relative velocity of the air stream moving across the particle. The drag force is what liberates the target particle from the substrate and gets it into the air stream.

Once the particle or droplet is within the air stream or hose, the continued movement of the particle is governed, no longer by drag, but by the pressure differential across the particle (lower on the downstream side, higher upstream). This is because after the particle is moving, it accelerates and approaches the air stream's velocity, thereby lowering the relative velocity of air across it, and reducing the drag felt by the target. At this point, a free body diagram of a particle reveals that the pressure imbalance on the target particle is greater than the drag and is responsible for continued movement.

This is how vacuum cleaning systems work, and you can prove this to yourself with a shop-vac in a little experiment. Such vacuums are often capable of producing over 100 aCFM (measured as the "actual" inlet conditions of temperature and pressure, which is called the volumetric flow, not mass flow such as SCFM. If you ever see CFM, this means actual, and for a mass flow such as SCFM, the "standard," or "S" must be indicated.) and 120" of water column vacuum (And remember that it takes ~27.7 inches of water column to equal 1 PSI). Then put a coin on a flat surface, and while the vacuum source is off, place the vacuum hose over it so the hose opening is normal to the surface. This will drastically reduce or prevent any air from entering the hose when it is on, however the vacuum produced in the hose will be the maximum the vacuum source can develop. Then turn the vacuum source on. Even though your source may be capable of even greater vacuum levels and flow rates, the coin will not come off the surface. Next, tilt the vacuum hose to establish air flow. The coin will come off the surface and you will hear it clunking down the hose!

For pesky viscous liquids, it is often necessary to help induce the drag needed to liberate the target from the surface it is on with an air knife.

Refer the following link:

http://www.exair.com/en-US/Primary%20Navigation/Products/Industrial%20Housekeeping/Drum%20Vacs/Pages/Drum%20Vac%20Home.aspx

This will help you to convey the sludge in both directions.

RAMARAJ.T

jsramraj@gmail.com