I'm looking for a commercial source for a pneumotachograph.  This is a tube with a
flexible (but stiff) flap in the flow path, with ports on either side to measure
differential pressure.

I used this device on a project measuring respiratory flow in anesthetized patients
in the Anesthesia Department at Ohio State University Hospitals about four{*filter*} years
ago.  Although we used a Validyne pressure transducer to measure the differential
pressure, I did not keep track of the vendor of the pneumotachograph.

I'm looking to use a similar technique to measure the flow of automobile exhaust gases.

Thanks in advance for any help you might be able to give me!