The true unions I have been using are adjustable. The adjustments can be made inside of the valve. Also, they have an arrow marking on one side of the valve which indicates the flow direction. I had one that leaked when installed backwards. Maybe try taking the valve appart and make sure the inner seals are clean. Not sure what is the correct tool to use for opening up the valve though.
http://www.spearsmfg.com/V-4/V-4-0305/044_BVTG.pdf