I'll second that...

This topic seems to repeat itself over and over, at least with respect to Festo Fittings and their appropriate usage. If its on the suction side, its just not a good idea for the reasons Harley mentioned. If you MUST use a Festo or similar style of union fitting on the suction side, make sure its up stream of the UAT so you can catch the bubbles and at least visualize the accumulate leakage over time. Barbed fittings, or preferable captured barb fittings like the original UAT use, are the preferred method of joining hoses in less that atmospheric conditions...

Kelly