need advice w/ a compressed air flow switch to plc

Project: install an air flow switch to monitor cfm and remote start one of 4 compressors ranging from 30cfm to 150cfm, depending on the demand needed. Can someone recommend an air flow switch that has analog output for a PLC. Thanks.

Are you sure you want to monitor air flow? Is this an air supply for air-actuated equipment like valves, pistons etc?

I would think controlling based on pressure would be a better option depending on what the air is being used for. Are these compressors fixed or variable speed?

To be technically correct, a "switch" is normally a point device. It's either on or off. What you really want is a flowmeter I'd suspect. For airflow, you could look at differential pressure using an orifice plate. But I would definitely consider using pressure as your process value.

Pressure transmitter dedicated for air compressor applications

http://www.danfoss.com/BusinessAreas/IndustrialAutomation/Pressure+Transmitters/Air+compressors.htm

I'm getting picky and crotchety in my old age, I guess. A switch has an on/off (discrete) output. An analog signal indicates a transmitter.

Dwyer, Eldridge Products, Sage Metering, and many other sources provide both. You can also look at Omega Engineering and McMaster Carr sites.

Here is one:
http://proportionair.com/products/electronic-flow-controls/f-series-flow-monitor/

Hedland has many flow meter options to choose from, including the analog output. I have one that has been in service for a while now with no issues.

Dave