Established History   Lasting Partnerships Firms that partner with Hartzell tend to have lasting relationships with the Company. The combination of production efficiency along with quality end products makes Hartzell the preferred manufacturer for many companies worldwide. Yellow Springs Instruments Since purchasing Hartzell in 1974, David Vickroy has worked with Yellow Springs Instruments (YSI). YSI is integral in water quality analyses and environmental testing. Their products are used around the world and Hartzell is a key supplier for the housings that their testing equipment fit into. As a trusted sheet metal components supplier Hartzell has maintained lasting relationships with firms just like YSI.