The Venturi Effect and InvisiPac

The Venturi effect is named after an 18th century physicist from Italy named Giovanni Battista Venturi. Rumor has it he first noticed the effect when drinking a beer through a straw, so his drinking buddies named it after him.

The Venturi effect says that as a fluid or gas flows through a constriction, its velocity increases, but its pressure decreases, creating a partial vacuum.

A vacuum is when the pressure inside something is less than atmospheric pressure - so it sucks. By saying, “It sucks,” we mean that atmospheric pressure being higher than the pressure inside the something actually pushes the fluid or gas along its way. Many describe the effect as a vacuum or sucking. 

In industrial packaging terms, the Venturi effect is why adhesive pellets moved from the hopper or feed bin into a hot melt delivery system.

Here's how it works in the Graco InvisiPac. We have a melter that melts the adhesive pellets, a hopper that holds the adhesive pellets, and an airline and vacuum transfer hose that go inside the hopper.

1. The airline and vacuum transfer hose are attached to either a wand with a shaker head or a vibration arm attachment. (Neither the shaker head ball nor the vibration arm themselves have anything to do with the Venturi effect. They just keep the pellets from sticking together.)
2. The shaker head shakes due to a ball inside of it
3. The pressurized airline is attached to the head or base of the wand.
4. The pressurized air goes into the base and moves up the wand, creating a low pressure area and forcing adhesive pellets up the feed tube.
5. The adhesive pellets mix into the stream of pressurized air and are carried off to the melter.

In other words, the passageways direct the pressurized air into and up the wand, essentially sucking or vacuuming up the adhesive pellets, carrying them off to the melter to be melted. 

Graco's use of the Venturi effect does not only apply to packaging and the InvisiPac Tank-Free Hot Melt System. It also applies to other products.

For example, the AirPro™ Air Spray Siphon Feed Gun uses the Venturi effect to move liquid coating – like lacquer, paints and stains – from a cup or reservoir to a sprayer for automotive, metal, wood and other applications