Does creating a vacuum using compressed air make sense?

In many industrial applications, it is common to use a so-called venturi vacuum pump or vacuum generator for vacuum applications ranging from pick and place to vacuum leak testing. The venturi operating principle involves sending motive air through a constricting nozzle shaped like a bowtie. This then creates an area of low pressure at the expanding side of the nozzle. By adding an intake connection at the constricted point (middle of the bowtie), gas molecules are pulled into a flow as pressure is equalized and as a result, this provides a suction force (vacuum) at the intake connection point as needed for the application. However, does this really make sense? 

Why make this argument you ask? Well, there are 2 main reasons:

1.       Converting electrical energy to compressed air (via a compressor) to vacuum (via a venturi) adds one extra step and leads to further efficiency losses and additional equipment to maintain and monitor.

2.       Less possible leakage in the (supply) piping assemblies as the maximum pressure differential is 1 bar (14.7 PSI) and not 6 bar (88 PSI) as is common with compressed air lines.

While yes, the rationalization can be made that compressed air infrastructure is already in place in many facilities (so no additional capital expenditures are required), what is the added compressed air demand for the venturi vacuum application that requires continuous air supply? Also, what is the total effect on the other equipment being served by compressed air? For example:

1.       From my own direct experience at Nolek; leak test systems and instruments used compressed air to not only control pilot valves, but also process valves with spring-regulated returns. For a piece of equipment at the end of the line, the pressure drop on occasion caused valves to open and close impacting the leak test system uptime and test results.

2.       In another instance on a pressure decay test where the test pressure was close to its limit, pressure drops would cause a “pressure not made" fault on the leak test instrument and thus the test was aborted. This not only added additional cycle time, but also led to a frustrating investigation by the maintenance team which resulted in the incorrect conclusion that there was a leak in the system. In the end, by simply putting a pressure gauge on the test port, the variations in supply pressure were easily identified.

The solution is to opt for mechanical vacuum pumps either in the form of a larger capacity central system or as smaller capacity pumps at the point of use. A central vacuum system operating at a low pressure is not very demanding on the pump. Depending on the vacuum level to be maintained, additional energy saving measures can be implemented such as turning off a pump(s) or using a VFD to meet demand.

I am not saying there is no place for compressed air in a factory environment because there is. However, for any vacuum-related applications, it is worth doing an audit to determine what the best solution is.