Recently we worked with a customer that needed to control the pressure in a reaction chamber between -200 to +200 cmH2O. However, though the customer’s building had an ample supply of compressed air, they had no vacuum source. Without suction, they were unable to reach negative gauge pressures. We went to work finding a solution that not only met the customer’s needs but could be added directly to the product they were purchasing. By installing a Venturi vacuum generator on an Alicat Dual Valve Pressure Controller (PCD), the customer was able to use their compressed air source on the system to create the necessary suction for controlling to sub-atmospheric test pressures.
What is the Venturi effect?
When fluid flow moves from a less restrictive to a more restrictive environment, its velocity must increase – such as spraying water from a garden hose by placing your thumb over the open end. According to Bernoulli’s Principle, this increase in velocity is associated with a drop in pressure. Thus, fluid flow passing through a restriction will have a resultant pressure drop – this is the Venturi effect.
How to use the Venturi effect to create a vacuum
For our customer above, we added a third party Venturi vacuum generator on the exhaust valve of a Dual Valve Pressure Controller. This turned out to be a size-conscious and cost-effective way to create a vacuum without adding a vacuum pump into the system.
It works like this: The Dual Valve Pressure Controller is designed to allow flow to easily escape through the second valve as needed to maintain constant or near constant pressure in the system. In this case, the Venturi vacuum generator accepts a compressed air inlet and flows this through a restriction to create an induced vacuum of about one PSIA, which is plumbed to the exhaust valve of the Dual Valve Pressure Controller, utilizing the compressed air flow to create a vacuum.